srimech

Turing Machine and Maker Faire

2011-03-16T15:41:00.000-07:00

Here's a video I shot at Maker Faire UK 2011. I took the Turing machine along having just rebuilt it without testing, but it worked fine over the weekend after a little prodding and adjustment. I don't think everybody understood it, but everyone was positive about it and those that did understand what it did seemed very amused by it.

I didn't get much chance to have a look around the rest of Maker Faire, but it was an excellent event with some great minds getting together to create some great hacks (a video of Kinect controlled Tesla coils is doing the rounds at the moment).

Now that deadline's over, I can go back to the drawing board and start thinking about how to make a more reliable, precise version of this machine, or a more powerful machine which could actually demonstrate something useful - which would be better than explaining that this Turing machine would take months to add two numbers together.

3D printed cellular automaton

2011-03-06T15:50:00.000-08:00

Work on the Turing machine continues steadily, but in the meantime I have been working on a backup plan for Maker Faire. Since I have a fair amount of spare time when I can't get to London Hackspace to do stuff with drills and hacksaws, I started work on a 3D printable automaton. The result is in the video above. It's missing two levers since I plain forgot to include them in the order, and this prevents it from actually computing anything - but this video shows the robot reading input data and altering the output data. When the levers are in place, it'll only move some of the output data, thus doing something interesting.

The input data is the row of ball bearings on the bottom of this video. They're all ones for the purpose of this video. The output data starts off as all zeros, and gets set to ones as the machine moves along. In doing so, the machine calculates the (n+1)th row of a rule 110 cellular automaton (top row) based on the nth row (bottom row).

Although it's a lot simpler than my mechanical Turing machine, it does exactly the same function - but it needs replacing manually at the end of each row (generation). Moving in only one direction is a really big deal, and makes everything much simpler.

Both this and the Turing machine will be on display at Maker Faire UK next weekend in Newcastle (12th & 13th March). At least one of them will be working, but sadly I've had to forego steam power in order to run it indoors.

Turing machine preview video

2011-01-08T13:46:00.001-08:00

Here's some video I shot at London Hackspace last weekend. The machine isn't working properly, but this should show roughly what it'll look like when it does. There's some mild swearing on the soundtrack; mute it if that offends you.

I'll be back at the Hackspace tomorrow, making another lifter (5th revision!) which should make it easier to pick up ball bearings and allow more space for a better centering system when the ball bearings are returned to the track.

I've been accepted to Maker Faire UK in Newcastle in March - I'll have the machine running on a stand there with some more cellular automata stuff. See you there hopefully.

December machinery

2010-12-30T21:27:00.001-08:00

The Turing machine ran three instructions in a row on Wednesday morning. I caught the 9am Tuesday train down to London Hackspace and worked through till 9am on Wednesday. The only problem remaining is getting the ball bearings to land reliably on the correct grid space. Direction change and movement are all solved problems now. I've added a gate released by an existing cam to stop the ball bearings exiting the machine too quickly, but the ball bearings often miss their correct grid spots.

This can be fixed by placing guards onto the grid, but I really want to avoid modifying the grid. Modifying an infinite tape requires infinite effort.

BigTrak + IGEP

2010-12-22T14:42:00.001-08:00

So here's what I've done with the BigTrak so far. I've mounted the IGEP on the back, mbed in the nose and arranged battery power for all the electronics and set up WiFi to remote control it. Boring technical details are at http://www.srimech.com/projects/bigtrak/. The audio on the video is poor, sorry about that. I wanted to be able to hear the motors and my voice is pretty soft at the best of times.

Annoyingly, the biggest challenge by far has been getting the drivers working on the IGEP. It's a neat board, but not very popular so there isn't much community support out there for it. It took me a couple of weeks to get WiFi and usb-acm (necessary to talk to the mbed) working at the same time, and the next challenge is to get it to recognise a USB webcam.

November Turing machine update

2010-11-24T15:03:00.000-08:00

Had a couple of days to work on the Turing machine during November. It's now on its fourth revision lifter, this time there are two lifting arms, one which will stop at the top of the state box and the second containing the magnets which will continue on, so the magnets are separated from the ball bearings at the top. This seems much more reliable. It needs a longer movement on the string which lifts the arms up, so there's a pulley system to double the effect of the cam lever. I've also made some changes to the reversing mechanism, using a weight which is just slightly stably balanced so requiring a very small force to switch over to the other direction. This should be operating at the end of another day's work.

Robot Hackday success

2010-10-31T14:14:00.000-07:00

Nearly three years ago I wrote a little blog post about the MUTR micro rover kit which I'd just received then. I put together a basic rolling chassis then but then got distracted and didn't do anything more with it - until this opportunity came up.

Enter Robot Hackday, a day organised by MadLab and HacMan. People bring down old electronic junk and attempt to make automata out of them. We succeeded in making an army of wonderful robots, from scribblebots and shaking Altoids tins to furry tanks with glowing eyes. It was great to have a bit of banter with other hackers as we tried to get a robot ready within the day. One of the special guests this year was Tim Hunkin, a hero of mine since he presented The Secret Life of Machines many years ago. Tim's a really friendly chap and he spent ages helping me get my robot working.

In the photo is WrigglyBot, the robot I built on the day. I seem to have been photobombed by a robotic raptor. Someone else there (I forgot your name, sorry) named it as the front of the chassis ended up low enough to the ground to scrape chewing gum off the floor. The axles needed trimming to fit both gearboxes side-by-side, and then I drilled holes for the rear axle and redrilled the rear wheels so they were loose on the axle. There are three relays controlling the motor, one does the forward/reverse control for each motors, and the third is the main on/off control for both. As it stands, it can't run just one track at a time.

The relays are switched by the ever popular ULN2803 chip, and the whole caboodle is orchestrated by an mbed board. This is the first thing I've used an mbed for, and apart from a minor panic when MadLab's wifi left me without access to the mbed online compiler, it worked very nicely - certainly a lot less hassle to program than my usual microcontrollers. There's two batteries on board - the main 4x C cell runs everything, and would have run the mbed but it kept resetting when I switched the motors on, so I put in a separate 9v battery to run that.

The only problem is the clip-in worm gear sets. The worms tend to rise up when the gearbox is put under strain, and this will strip the gears if allowed to run for too long. Mine was still slipping despite lots of Araldite and wire holding the motors down. I think they need something to hold the worms down at the front.

Thanks to everyone at MadLab and HacMan, that was a great day out.

September progress on the Turing machine

2010-09-26T15:55:00.000-07:00

As of this evening, all the cams are working correctly and the main sequencing events (lift data, reset direction, drive) are working. The drive system is driving too far backwards, three grid spaces instead of two. The data lifter also requires far too much force to drive. Ideally, this could be counterbalanced by adding some lead weights, but there isn't a great deal of space to add anything right now.

The cams have been a lot more problematic than expected. Attaching a cam to a 5mm steel shaft requires some sort of flange which itself has to be secured to the shaft. I made several flanges out of aluminium which were meant to be fixed to the shaft by set screw, but in a lot of cases the thread failed before I could tighten the set screws enough to hold the cam. Filing flats on the shaft helps to some extent, but means the angle of the cam has to be decided then and there. When this machine is completed I think there might be quite a lot of subtle adjustment needed in the timing, so I'm reluctant to go filing or drilling the drive shaft right now.

Forward/reverse movement has been a cause for some concern. The 'punt' mechanism is working, but I'm not convinced it will be reliable in the long term. I also have plans for a more conventional forward/reverse gearbox and have a sprocket which will interface with the steel grid, thanks to Razorlabs.

We'll see how it goes.

A modder's guide to the 2010 BigTrak

2010-09-23T16:39:00.000-07:00

Zeon Tech have started making a replica of the Big Trak (or bigtrak, or BigTrak, whichever you prefer) so I bought one to see how it'd work as a mobile robotics platform.

In the box you get the BigTrak, a manual and a pack of stickers to make it look like the illustration on the box. I think having stickers to apply yourself is great, so please continue with that, toy companies. As with the original, the centre wheels are driven and the front and rear axles are free. The front axle on this one allows some vertical movement, although it's not sprung. This presumably allows the machine to keep the weight on the middle wheels at all times, although it does mean it will rock back and forwards a little bit. The whole unit runs off 3 D cells, unlike it predecessor which needed a separate 9V battery, presumably to run the computer.

Underneath, there are plenty of screws to remove. The only difficult one is at the back, highlighted by the yellow arrow here. The plastic moulding on the back will come off with a bit of prodding, and you can see where the clips are if you remove the rest of the screws and open the case up a little. By pressing in in four places, it will come free. Don't bother removing any of the screws from the wheels or the grey drive unit underneath yet.

Once all the screws are removed, you can see inside. The ribbon cable goes up to the membrane keypad, which is unfortunately glued onto the case. However, the glue isn't strong and you can remove the keypad without damaging it. Wires at the front go to the 'photon beam' LED and speaker. One of the first mods you'll probably want to do is snip one of the speaker wires, although it will make programming the existing circuit board more tricky. The other wires go to the battery box and a tiny circuit board on top with the on/off switch and an IR LED; presumably the IR LED is for the trailer attachment, when that comes out. There's a lot of empty space inside the case, which is good news for modifying it.

Removing the ribbon cable and snipping the rest of the wires allows you to remove the drive unit. This is the least destructive way to get the drive unit out, as the controller board is soldered directly to the motors and can't be easily removed. The grey drive unit will now just drop out of the chassis. The circuit board is not particularly interesting, having two chips marked CE3962 which is the model number of BigTrak itself. There's a few discrete transistors on the underside of the board, which are probably the motor drivers. You might be able to modify this to operate the motor off TTL signals, but I'm not particularly interested in using it.

So now the important bit. A few more screws removed and you can see the gearbox. I was expecting this new model to have skimped a bit on the components compared to the original, but this actually looks good - it still has encoders on the second set of gears, and it still has the magnetic clutch between the motors. This clutch keeps the motors in sync if you drive them at roughly the same speed, to improve your chances of driving in a straight line. The motors look small, but they didn't have any problems driving on thick carpet when I briefly tried them.

I'm pretty happy with this; my next plans are to install my IGEP board on it and connect up a couple of electronic speed controllers to run the motors. You can see the IGEP mounted (not connected to anything at the moment though) and the BigTrak with the (badly) applied stickers to the left. Amazon seem to the be the cheapest place to get them at the moment; I paid £32.48 for one including P&P through a reseller.

Camping with dry ice

2010-07-30T17:24:00.000-07:00

Quick report: Is it feasible to take dry ice on a camping trip and keep your drinks cool with it? Yes, although it's not cheap or particularly easy. The results are however much better than car-powered cool boxes, in my opinion. You'll need to find a dry ice supplier who is either on your way to the campsite, or who will deliver to you before you set off. I found All About Ice, based in Hemel Hempstead, which was handily on the route I was going to take to get to Swanage. I paid 35 pounds for 10kg of dry ice pellets and a thick polystyrene container for them. The container is a cube about 40cm on each side. Needless to say if you want to pick up dry ice you'll need to get there during normal working hours, which probably means a day's holiday from work for you.

The next problem is transporting it - dry ice is constantly subliming into carbon dioxide gas, which will suffocate you in a closed container, and if you're driving you'll probably kill more people than yourself if that happens, so be really careful with it. This means you drive with all the windows open, and if it rains you get wet.

Once you've actually got the dry ice to a campsite, most of the difficult parts are done. You'll need another cool box, as you can't put food or drink straight into the dry ice container - it's about -86 centigrade in there. Put some heavy gloves on and transfer some dry ice into the bottom of a cool box, then cover that in a bit of cardboard and put your food or drinks on top of that. If bottles come into excessive contact with dry ice they will freeze and could shatter. If you need to cool something quickly, you can put another layer of cardboard on top of your beer and then shovel some dry ice on top of that. Now you can enjoy cold beer and wine well into the second and third day of the weekend and be the envy of the campsite. You'll probably only want to transfer a little bit of dry ice into a cool box at a time. I also found I could leave the cool block things you get for cool boxes in with the dry ice overnight without them exploding, but your milage may vary on that.

Lock the dry ice in your car when you don't need it, to prevent children and idiots playing with it - it will burn you if you touch it. Don't forget to give your car a few minutes airing with the doors open before getting in if the dry ice has been in there overnight. Don't put dry ice or any container containing it in your tent, for obvious reasons. Apart from that, the only problem will be disposing of it if you don't want to take the remainder home. Rather than just dumping it somewhere children or pets could burn themselves on it, you'll want to pour a lot of (ideally warm) water on it to disperse it. This could be quite a lot of water, so be prepared for a few trips to the tap.

Plans for a mechanical Turing machine

2010-04-13T16:35:00.000-07:00

This is a project I've been planning for many years. It's a design for a fully mechanical universal Turing machine. My self-imposed constraints are to use no electronic or even electrical components, to be driven by a single rotating input shaft, and to be constructable with simple hand tools, without relying on high precision parts.

Trying to design something like this is an interesting challenge, and something I've found I can work on entirely in my head when I'm stuck somewhere with some spare time and not even as much as a sheet of paper to draw ideas on. Some of you might like to stop reading here and try and figure out a design yourselves before this plan taints you.

I had most of the conceptual design finished at the start of this year, and it's taken until now to get a fully specified model made up in OpenSCAD. I think this is now ready to manufacture.

One of the most difficult initial problems is how to store a reasonable amount of data, such as the tape for a Turing machine without having to manufacture a large number of custom parts. My design uses ball bearings on a sheet of pattern perforated metal as the tape. The position of balls on the grid is the data, and the machine moves back and forward on the grid. To be strictly universal, the perforated metal sheet needs to be infinitely long. I haven't carefully examined the sheet RS have sent me but will assume it to be infinite for the time being.

I'll now try to describe how the rest of the machine works, which is pretty difficult and I don't think this will be immediately clear. I hope to have a working prototype soon which should make its operation clearer.

This schematic diagram shows the main components of the machine.

The next component after the grid and set of ball bearings is a lifting arm or raiser (red) which picks up the 'input symbol' under the read head and lifts it to the top of a block of channels not unlike a marble alley. The run needs to contain some state which will direct the ball down different channels, and needs levers which will update the state for the next ball, and set the direction the machine will move. It also needs to direct the ball back to a new position on the perforated sheet to 'write' the new symbol.

First in the run is the 'state box' (cyan) which diverts the ball down down one of two paths depending on the position of the gate. The position of the gate is the state of the Turing machine. Paddles on the gate also turn the gate as the ball falls, setting the new state of the machine. The output of this box is a ball in one of ten positions, representing the combinations of five input symbols and two initial states.

The next part is the 'direction box' (green) which has levers in some of the ten paths which will alter the direction of the Turing machine later on. If a lever is hit, the machine moves left, and if not, it moves right. The actual movement isn't carried out in this phase, as the falling ball won't have nearly enough power to move the whole machine, but it sets state which will be picked up later.

After falling through the state box, the ball falls into the 'maze' (orange) which maps the ten input positions into one of five output positions, which is the output symbol for the machine. A set of gutters under the maze will return the ball to the grid in its new output symbol position.

Behind the marble alley, there's a tower which performs the movement for the whole machine. A cam (blue) drives a set of three levers (brown) which move the machine. The bottom lever can be easily deflected from one side to the other while it's raised; this is done by a linkage from the direction box. The cam drives the levers downwards, where they engage with the grid and push the whole machine forward or backward two grid spaces.

There are other cams to run the raiser and to reset the direction box each cycle.

The whole machine rides on wheels which ride on top of the grid. Using round wheels on a square grid will provide a small amount of alignment so the machine doesn't drift away from the positions of the balls.

This machine is a 5-symbol, 2-state Turing machine. The configuration comes from Stephen Wolfram's "A New Kind Of Science", which shows this to be a universal machine. While it's relatively simple, it's also ridiculously inefficient and could not be used as a practical computing device. It's just meant as a demonstration of how simple a universal computer could be.

Fab Lab success

2010-04-11T05:02:00.000-07:00

This is a picture of two attempts at making a machine component. I'll explain what it actually does later, but this is mainly a post about how I made them.

On the right is my first attempt, cut by hand with a Dremel with a router accessory. As you can see, it's pretty rough, but it just about works - you can drop a ball bearing into one of the slots and it will roll down to one of the exit holes in the base. Sometimes they'll stick, so it needs a bit more work yet.

On the left is a CNC milled block which I was able to get made due to the opening of Fab Lab Manchester. I mentioned this a while ago when they made their press release, and they've just opened so I went along on Saturday. It's an amazing place and free to use on Fridays and Saturdays so long as you don't mind sharing the details of your project. This was cut using their enormous ShopBot CNC vertical mill.

I'd never got on well with 3D modelling programs and tended to use POVRay to model projects since I'm used to working with code rather than WYSIWYG editors. At Maker Faire UK this year I discovered OpenSCAD which is in some ways similar to POVRay - it takes a text scene description file and produces a 3D representation which can then be exported as an STL file - a format which milling machines and 3D printing machines can understand. The maze shown was just a piece of text in an editor on Thursday night, and by Saturday afternoon I'd been able to turn it into a physical object. For an amateur mechanical engineer like me, this really changes the game and allows a huge number of ideas that I'd never otherwise be able to realise. I'm very grateful to Fab Lab and especially Hayden who spent most of his afternoon showing me how to set up the mill.

If you're still interested in what it does, the diagram to the left might make it clearer. The idea is to drop a ball bearing into one of the central slots, marked by the yellow squares. The two columns represent two states of a state machine, and the five rows are the five different input symbols. Based on the state and input symbol, the ball bearing rolls down to one of five output holes. The vertical position of the output hole is the output symbol. In short, this is part of the control logic for a 5-symbol, 2-state universal Turing machine - the Wikipedia article may help explain this if you're not familiar with them.

Madlabs and Hackspaces

2009-12-15T16:23:00.000-08:00

2009 has been very interesting for collaborative hacking. Stockport Hackspace caught my attention first, and I went to a few meetings and met some very cool people there but trekking down to Heaton Chapel after work got a bit too much for me. Recently, MadLab started up in Manchester as well. I went along to their hackday on Saturday. They have a great working space of three floors in some of the otherwise unused buildings in the northern quarter. There were some great people there as well, mostly working on small robots from the high tech micromice to simple shufflebots. MadLab looks very promising and I'll take along some stuff to break apart and hack together next time they run an event.

Stockport Hackspace are planning on (and seem well on the path to) opening a Hackspace in central Manchester.

On the heavier side, PitStart garage caught my attention. It's a pay by the hour garage with tools included. I have to wonder how much I'd end up paying if I drove in and then made my car undriveable, as I often do when I try to fix things on my car myself. It's also in London so not a great deal of use to me, but I'd love to see more of this type of thing around the UK.

Golf GTI shakedown

2009-07-31T15:24:00.000-07:00

Faced with the possibility of 600 miles through England and France with five people in a car to accompany my parents on holiday, I decided to buy my own car.

Not wanting to take an easy option, I bought a 1985 Volkswagen Golf GTI Convertible. This replaced my previous but younger 1990 Nissan Sunny 1.4 LS, which was a remarkably reliable and well handling car if not particularly sporty.

This Golf is in good mechanical condition for a car of its age, and its chassis has been sealed well and is free of rust. I bought it from a private seller in Stockport and immediately took it to a garage for a check over. We fitted a new clutch, timing and alternator belt, and had both rear wheel brake cylinders replaced and the tyres re-sealed. This service cost almost as much as the car cost me in the first place, but I was expecting that.

The first run out was to Wales for a camping weekend. The fuel delivery problem became apparent during this run. It started kangarooing and cutting out while driving through the centre of Manchester, but with a good battery to keep starting it, it managed to get out without any serious problems. Once on the motorway it had no problems.

The Mk1 Golf GTI uses a Bosch K-Jetronic fuel injection system, which is an entirely mechanical multipoint but non-direct petrol injector system. A fuel pump under the driver's seat pumps fuel at injection pressure (I think) into an adjacent accumulator to cope with peak demands, which then feeds up to a fuel distributor in the engine compartment. The problem manifests as an infrequent but sometimes severe lack of power, often enough to stall the engine. My own experience from driving it makes me think there are large air pockets in the fuel, but I have been very wrong about diagnoses in the past. I think it's likely this problems does occur while driving on the motorway but is not noticed in the momentum at those times.

The fuel problem had been declared by the previous owner when he sold it to me, and he had done a lot of work to try and resolve it - fitting a new fuel pump, fuel distributor and injectors amongst other things but these evidently hadn't fixed it. Mk1s often suffer from rusted fuel filler tubes, and while this had been replaced on mine, there is a strong possibility of rust in the fuel tank contaminating or blocking the other systems. Just before leaving for France, I replaced the fuel and air filters as I had no evidence of their being recently changed. The old fuel filter did emit ominously brown fuel at the tank side when removed. I hoped the new filter would permit more fuel through and solve the problem.

As well as this, I replaced the fixed offside mirror which was deflecting under motorway winds with a decent one with remote cable controls. This would be especially important when driving in France. I also replaced the original cigarette lighter socket with a modern one which would accept an accessory plug without falling out, and correctly connected the passenger door lock so it could be locked and unlocked from the inside.

Unfortunately, at nearly the last minute I also noticed the reversing lights were not working. I had lighting problems with my old Nissan and patch wired them, but reverse lights are a bit tricky because UK law (as I understand it) requires that they can only be activated when reverse gear is engaged - a switch on the dashboard won't cut it. After a while prodding at a rather inaccessible switch unit on the gearbox, I decided to fix a microswitch to the gear lever housing in the cabin. I used Polymorph, a low melting point thermoplastic to construct a solid structure for the switch around the gear lever. I would recommend keeping a pot of this stuff around for emergency repairs to any engineer.

With that fixed, I set off for the Latitude festival. The fuel problem appeared once again while picking up a friend from Manchester, but after that there were no problems. Me and the Golf proceeded on to Saint-Barthelemy in Brittany and back, the only problem being an embarrassing incident while loading onto the return ferry. Near the top of the loading ramp, it cut out and would not restart for more than a few seconds, and this required us to raise the ramp and push it into position on the car deck. After sitting idle for 10 hours on the deck, it restarted with no problems and proceeded to drive back to Bolton via Hertfordshire without any further issues.

The fuel problem will be an interesting one to debug. A full inspection of the tank and the fuel lines will be the next project. One of the rear wheel cylinders also appears to be leaking again, but hopefully this will be fixed under guarantee.

"FabLab" opening in Manchester

2009-05-01T02:37:00.000-07:00

Some vague details have appeared in the press of a 'FabLab' opening in Manchester later this year. It sounds like a low-volume, general manufacturing plant. I'm imagining some CAM and 3D printers. This could be very exciting if it goes ahead.

News article: http://opensource.sys-con.com/node/940106

The main backers seem to be manufacturinginstitute.co.uk although there aren't many more details on there yet.

Electric pressure gauges

2008-11-09T14:01:00.000-08:00

Earlier this year I made a load average meter out of an old ammeter. But I've decided I want to use some even older technology, so I've been refitting some pneumatic pressure gauges so I can display information with them.

I got a load of old gauges from Empire Exchange, the little Mancunian goldmine that supplied the ammeter. Opening these reveals an arc-shaped copper pipe which deforms when inflated, driving a lever and gear which moves the needle. Now, ideally, I would control these using a computer-controlled variable pressure pneumatic source, but I don't have pneumatic mains in my house (not at 140 bar, anyway), so I've had to go for an electro-mechanical solution. It's a shame to cut the proper workings out of them, but I don't think they would have gotten any better life in their present form.

A servo motor is the obvious choice to get a controlled rotational movement. However, most servos only have a range of 180°. I need a range of 270° to use this meter properly. You can get servos with a greater than 180° range but they are quite rare, especially in the small sizes I need to fit into the gauge's body.

In order to get the 270° range I've used a rudimentary belt drive. I made a pulley for the gauge's output shaft by clamping the shaft into a dremel and using it as a lathe to turn down a larger plastic pulley to the right diameter.

The servo's output shaft is about 5.6mm diameter, so I made a pulley as close to 4.2mm as I could get it for a 1:1.5 enlargement. The pulley I made is rather rough, but no-one will see it in the finished product.

I've attached the servo to the gauge body with Araldite, and used polyester sewing thread as a belt, with two turns around both pulleys. The belt is tied to the servo motor's horn and fixed with glue at that point. Ideally, it would also be tied to the output shaft, but the tiny scale of the components make this kind of engineering impossible for me.

A real engineer would use a toothed belt or a gear drive for this - or make their own servo motor. But for a few hours' engineering in my kitchen, I'm happy with this solution.

I've tested this with a remote control system and it works very well. The biggest concern is slippage of the belt, but the exercise I've given it so far shows that it's actually perfectly repeatable - it doesn't slip at all.

The next steps are to replace the scale backplate with something like a 'load average' or 'spare memory' scale, and to rig up a servo motor driver so I can control it from a PC. Servos are very easily to control, just needing a PWM signal - a little easier than pneumatic signals in this day.

If you want to know why I bother to do this, you are probably not my target audience. :)

Opening a WRT150N

2008-11-09T13:37:00.000-08:00

Only a tiny number of people will be interested in this, but I recently had to open the case of a Linksys WRT150N router and found a few questions on the web asking how to do so. Doing this voids your warranty, of course.

First of all, find a T10 security torx driver. These are like standard Torx bits with a hole in the middle.

Start by flipping the router over and levering up the silver panel at the rear of the router. I'm calling the rear the side which the antennae are attached to. The rear half of this panel will pop out of the body, but the front is attached with hooks which will break if you try to lever up the front half first. Once the rear half is free, the front half will slide off easily.

This will expose four security torx screws. Remove these.

Now you can remove the top and side panels. Pull one of the side panels and its side of the top panel away from the router at the same time. The hooks which hold the side panels on should pop open one at a time without damaging anything.

Repeat this with the other side panel. You should now have a completely disassembled WRT150N, so you can get at the serial port connections you want to attach to.

Tea-making with gas and electricity

2008-08-10T04:58:00.000-07:00

B3ta recently asked whether it was cheaper to make a cup of tea using an electric kettle or a gas one. My gut feeling on this was that gas was cheaper, because gas is a lot cheaper than electricity per unit energy. I've done an experiment to see which is actually better.

Starting with gas, I put a mugful of water in a steel saucepan and heated it over a low flame. I can measure the amount of gas used using my gas meter. I've completely shut off my central heating boiler, including the pilot light, so no other gas is used during the experiment.

This took 0.0092 cubic metres of gas to bring it to the boil. I'm calculating the energy and cost based on my last gas bill, which explains how to convert from cubic metres to kWh - ultimately by multiplying by 11.0786. So I've used 0.102 kWh. I pay 2.88p per kWh for gas. USwitch.com reckons I could get gas for 2.86p from another supplier, so I'll use that. That makes a total of 0.29p.

Next I set up an electric kettle with a plug-in power meter. I've got to use half a litre of water to cover the element and make up the 'minimum' mark on the kettle, which is slightly more than the mugful I boiled in the saucepan. To boil this took 0.06kWh. The cheapest electricity I could find on USwitch was 11.21p/kWh, so this cost me 0.67p. Even given the inaccurate measurements in this experiment, gas is the clear winner.

But what if I've got friends round? I did a test with a large teapot full of water as well. This time, the saucepan took .281kWh for 0.82p, and the kettle took .140kwH for 1.57p. Still nearly double the price of the gas option.

Boiling speed is another factor - the gas saucepan takes a lot longer to boil than the electric kettle. I did some more experiments, using the gas turned up higher than I normally would. I expected this would waste gas, because a lot of heat escape round the side of the saucepan. However, it was barely any extra. There's probably a 'sweet spot' for the gas flow - too high would waste gas, and too low would take so long to boil that heat gets a chance to escape from the saucepan. Still, I couldn't get it as quick as the kettle. The kettle isn't a fast boil one - it's about 2.2kW. Even so, in all the experiments I measured time for, the kettle is twice as quick. So for the extra third of a penny it costs to boil the electric kettle, and the convenience of having an automatic off switch, I may well stick with that for the time being.

You'll notice that the kettle uses less energy despite costing more. Does this mean the kettle is more efficient? Not necessarily. The kettle is more efficient in itself than the stove and saucepan, but a lot of the electricity comes from gas in the first place. About 36% of our electricity comes from gas-fired power stations, and the best stations are about 58% efficient. Another 37% comes from coal, but I haven't found efficiency figures for those yet. If our electricity came entirely from gas, the kettle would use about the same amount of energy as the stove. To do a fair comparison you would also need to know how efficient the national electricity grid is, and how much energy is used in pumping gas around the country.

http://www.berr.gov.uk/files/file39569.pdf
http://www.the-eic.com/News/Archive/2006/Nov/Article2799.htm

The data in full:

Fuel	Quantity	Speed	Time (s)	Volume of gas	kWh	cost/kWh (p)	Cost (p)
Gas	1 cup	slow		0.0092	0.102	2.86	0.29
Gas	1 cup	fast	192	0.0100	0.111	2.86	0.32
Gas	1 teapot	slow	1376	0.0254	0.281	2.86	0.8
Gas	1 teapot	fast	506	0.0258	0.286	2.86	0.82
Electric	1 cup	n/a			0.060	11.21	0.67
Electric	1 teapot	n/a	213		0.140	11.21	1.57

The by-products of potato juice

2008-07-27T15:33:00.000-07:00

Today I have mostly been performing silly experiments in the kitchen. I like potato pancakes, but they are problematic to make because the moisture has to be removed from the potatoes before frying them. This usually involves dirtying a clean cloth, or trying to squeeze the moisture out by hand which doesn't work well. I've also tried using a ricer on raw grated potato which is quite effective.

I had a brainwave today - realising that I already had a device which does this job, namely a juicer. I pushed three potatoes through the juicer, and kept the pulp that normally gets discarded. Mixed with some chopped onion and seasoning, this makes really good, fine potato pancakes. I wasn't brave enough to try drinking the potato juice.

An earlier experiment to try separating freshly brewed coffee from its grounds using the juicer didn't work so well. It just tastes like soil.

12 volt mains

2008-06-05T15:21:00.000-07:00

If you like gadgets as much as me you probably have a large number of AC adaptors with power bricks cluttering your house up. A lot of these have different output voltages, but I have quite a few that deliver 12 volts, or claim to. Is it possible to replace some of these with a single transformer to simplify the wiring and increase efficiency?

The experiments I've done so far suggest that the first part is quite possible, but surprisingly, I couldn't run my appliances as efficiently with a single power supply than with individual bricks.

The appliances I used for this were my Netgear ADSL Wifi router, my 20" LCD TV, and my mini-itx based server computer.

The first step was to give each a common connector. I split the cable on each and attached a PC drive power connector on each side. Drive power connectors are cheap, meant specifically for 12V and can be plugged straight into an ATX power supply.

Having done that I reconnected them to their original power supplies and switched them all on, checking the power consumption for each. Measured at the mains socket with a plug-in power meter, I got: PC on idle: 28W. TV: 50W. and the router: 7W. Total 85W. Incidentally, if you repeat this experiment, it might be better to plug all those into a power strip and plug that into the power meter, in case the meter has some non-linear error.

Using the first attempt - an "L&W" 250W power supply used 48W just to run the router and PC - obviously less efficient. The TV wouldn't work properly at all - I got sound but no picture. A quick check revealed that the 12V output of this power supply was actually only raising 11.05V unloaded - which presumably is not enough to power the TV properly. The PSU also used 12W without any load at all.

I tried again with an older Opus PSU which had the same problem powering the TV. It also used 8W unloaded.

Next was a Morex PSU, only a 200W model for a micro-ATX system but this was evidently of better quality and managed to get the TV running. However, just the TV and PC drew 92W from the mains - over the limit before the router was connected. It also drew 11W when idle.

The last test was my bench PSU. This is a bit of a beast, rated at 40A continuous, but given its higher cost I thought it might stand a chance of being more efficient. No such luck though - with all three appliances it drew 110W, consuming 18W unloaded.

So, while it might make the wiring neater if done properly, I've yet to find a power supply which will do the job more efficiently than using individual power blocks.

I suspect that computer PSUs are not the best choice for this job, as they are probably geared towards delivering a very stable smooth 5V and 12V rather than efficiency. The power bricks are not, so far as I can tell, very stable in their output voltage, probably relying on further conditioning inside the appliance.

As usual, I wouldn't recommend anyone else trying this for themselves - running things on too low a voltage could damage them, and not all PSUs output the voltage they claim - the router's power brick, for example, delivers 16V when unloaded.

Asus Eee 900

2008-04-30T13:51:00.000-07:00

Hooray! Despite making me jump through a few hoops to verify my identity, Dabs came through and delivered my Eee 900 today. I'm posting from it right now - the keyboard will take a bit of getting used to but it's a lot easier to type on than my previous UMPC. It'd be hard to give a negative review to something I've just spent 330 quid on but it is very good so far. It's a lot better built than I'd been expecting - it may look like a toy but it's very solid. Next step - apt-get emacs and pygame.

Toaster video

2008-04-17T15:21:00.000-07:00

I've been playing with my digital camera, trying to make a better video for the turbo toaster. The results aren't perfect, but still better than I expected for about an hour's work. The title and fade in was done with Kdenlive, which I found really easy to use. Pity that it doesn't seem to anti-alias the text properly when fading to the video clip. I brought up the colour a bit using mencoder with a few filter options. Anyway, there you go, flying toast in full motion video.

From the archives

2008-04-11T15:51:00.000-07:00

I've uploaded a few of my older posts from my wordpress installation - the LED message board modifications, the event report from Robot Wars 2003, and the Turbo toaster.

Load Average Meter

2008-03-19T14:54:00.001-07:00

I found this old milliameter in Empire Exchange in Manchester. It was built sometime in the 1960s. I then printed out a new scale for load average, turned the original scale plate around and glued my new scale onto the back, so as not to ruin the original one.

I've used a USB interface board from Maplin to drive it. The interface board has open collector PWM inputs, but the meter needs a bit more power than the board can supply - about 100mA on its smallest scale to go full scale. To get power, I've drawn off a drive power connector from the motherboard. The last component is a small perl script that does a bit of maths to convert the computer's current load average into a duty cycle.

Moving from Wordpress

2008-03-07T14:11:00.000-08:00

While I'm very impressed with Wordpress, maintaining my own installation is taking up a bit more time than I'd like. I don't write posts very often and Wordpress seem to come out with a new version more often than I blog. I've decided to move over to Blogger so Google can take care of the service. I'll either write a script to keep them in sync or move srimech.com over to a republishing system.

MUTR Micro rover

2007-12-08T12:57:00.000-08:00

I found this little tracked robot platform at mutr.co.uk. It's quite difficult to find tracked robot platforms (or even the components) cheaply, but this is very nice for the ~ ten pounds they charge. It contains the tracks, wheels, motors and gearboxes, an aluminium plate for the chassis, fixing screws and some three-way switches and wire. It needs a bit more than just assembly to get it moving - I had to fold and drill the aluminium and glue some of the wheels together, and I found the motor tended to rise out of the gearbox if I didn't tie it down with some copper wire.

Somewhere I have some infra-red proximity sensors and a camera board I'd like to attach to it to make it into a proper robot. It'll need a suitable battery and some motor controllers - the Electronize controllers I have at the moment are a bit too big for it.

MUTR sell a lot of useful stuff - I got some Nitinol memory wire at the same time, which is very interesting stuff. Their £5.80 default delivery charge is a bit annoying for small orders, but handily I have some colleagues who also buy from there to share costs with.

ZX Spectrum Laptop

2007-10-28T17:07:00.000-07:00

The ZX Spectrum laptop is a combination of two old computers: a ZX Spectrum 48k and a Toshiba Libretto 110. The Spectrum is an iconic British computer from the 1980s, selling in huge volumes (although I was brought up on a BBC Micro myself), and the Libretto was one of the first truly tiny x86 laptops, quite amazing when it appeared about a decade ago.

The modification keeps the case and keyboard of the Spectrum and the main circuit board and display unit from the Libretto. Connecting the keyboard was by far the most difficult part. I went through several ideas to try and figure this one out.

The PS/2 port would be an obvious choice, but the Libretto only has a PS/2 connector on the docking station attachment, which was too bulky to fit into the Spectrum case. It’s the same story for the serial and parallel port. The only standard communication options on the mainboard are the PCMCIA slots and the IrDA port, and I wanted to keep the IrDA port free for other communications. So the next idea was to try and replace the Libretto’s keyboard more directly.

Luckily, the Libretto’s keyboard unit contained no active electronics and was just a matrix of contacts on a plastic membrane. Logically then it is possible to simulate the keyboard by shorting various lines at the point they connect to the motherboard. However, the Libretto’s keyboard connects to its main board by a 0.8mm pitch flexible circuit connector, which is rather difficult to connect to. I tried several attempts to connect flying leads to the membrane, using glue and silver paint, which were mildly successful. The two keyboards are logically just arrays of switches with row and column connectons coming out, although the Libretto obviously has more switches, having an 8×13 matrix compared to the Spectrum’s 5×8. The challenge then was to pick out the particular rows and columns to use on the Libretto so that each key on the Spectrum made a valid keypress - some row/column combinations might have been ‘blind’ for the Libretto, for all I knew. I traced the keys to rows and columns on the Lib - mainly using digital photos of the membrane and a flood fill tool.

Meanwhile, the physical construction provided some more challenges. I had to cut away quite a lot of the case to fit in the display, and getting the display straight and closing nicely was quite fiddly. The case also had to be made a bit deeper to fit in the battery, so I made up a frame to separate the top and bottom halves of the Spectrum case.

Having done that I could switch on the Libretto and make a few keypresses on the Spectrum keyboard - nothing very sensible since mapping a letter to the correct one would have been impossible. Before I got very far, though, I realised the connections to the membrane were unreliable and decided to solder directly to the Toshiba’s motherboard. This is a very tricky task with the 0.8mm pitch, and I didn’t get all the connectors but I did manage to get the 5 columns and 8 rows I needed. The result isn’t very pretty, but did look a lot nicer than the rat’s nest made by the membrane keyboard and glue mess. The Spectrum keyboard remains connected by glue and paint, although it was easier to make a robust connection to the wider membrane on its keyboard.

With those all attached reliably, I made up a new keymap for linux so the keys would map correctly, and could actually type properly on the Spectrum keyboard. Getting Debian onto the Libretto was the next challenge. The PCMCIA-attached CD ROM drive that came with it had packed up, and the floppy drive is a nonstandard type that won’t work for Linux installations. There isn’t an ethernet port, even on the dock, so the best option was to make up a bootstrap image on the Lib’s hard disc, return it to the Libretto and boot it from there. This seems to have worked fairly well.

The remaining problem, which I haven’t figured out yet, is how to get some communications so I can download and install new software without resorting to the dock (I have to take the mainboard out of the case to fit it in the dock, so it’s not very desirable.) The PCMCIA ports would seem the best option, but I haven’t been able to bring up an ethernet card in it yet. The IrDA port is also a possiblity, although downloading any data through that might require quite a lot of patience.

So, what use is it? Well, the obvious application would be to load up a ZX Spectrum emulator to have a portable retro games system. It’d also be good for making notes while on the road - the batteries are good for a couple of hours, which surprised me considering they’re ten years old. Otherwise it’s just a bit of an objet d’art.

Busy

2007-07-18T12:31:00.000-07:00

I've not had much to post about recently, due to a rush at work, not being able to get to Newark Kit Car show, and being on holiday. I'm working flat out on a little retro computer project at the moment, which I'll detail later, but for the moment I'll just post this picture of a method I'm experimenting with to attach flying leads to flexible circuits.

Theremin!

2007-05-30T15:38:00.000-07:00

A few days ago at work we got some new computers in and decided to call one of them 'Theremin' since all the others were named after instruments and we were running out of ideas. A quick browse later and I found Art Harrison's web site on Theremins. This is built from his '2006 Minimum Theremin' instructions and I found it pretty easy to find all the components at Maplin. It's a simple design, meant more for demonstrations and science fairs than musical use - Art has designs for more sophisticated theremins on his site. I've no doubt reduced its musical quality by deviating from his design, but you can still get a tune out of it. I've left off the tone control - it's an preset on the board rather than a proper control - but you can alter the range quite adequately by adjusting the length of the telescopic antenna.

Dan's from-scratch barbeque

2007-05-20T15:39:00.000-07:00

Last weekend my friend Dan invited us all down for a barbeque. A generous offer anyway, but this had the added highlight that Dan had built the barbeque from scratch. It's a fine piece of engineering - perhaps not quite as stable as a brick barbeque but it served very well and cooked plenty of food for fifteen or so hungry guests over the weekend.

The construction materials are (so far as I remember) 1/2" steel bar and angle, some thin steel plate, steel mesh and those corner strips plasterers use - the closest thing most DIY stores will have to perforated angle. If anyone else has a go at this, my one piece of advice would be to avoid galvanised metal, as can give off some nasty fumes if heated. Compared to the quantities of ethanol usually drunk at barbeques though, it's probably a drop the ocean.

Dan also made a giant jenga set by cutting up some planed timber - a very quick and effective party piece. Pictures of that are in the gallery.

Sugar Fab

2007-05-10T16:30:00.000-07:00

EvilMadScientist's sugar fabber promoted quite a lot of discussion in our office today. Using sugar as a fabrication medium is inspired, but we wondered whether we could use something more accurate than a hot air gun to fuse the sugar. Using a high-power laser would seem ideal, but I think there's a lot of milage in using a lamp (or lightbulb) and a moving lens or mirror to focus heat on a particular area.

Ghetto 100Base-TX

2007-05-10T15:57:00.000-07:00

Networking Today's top tip: Don't slam your network cable between a door and a door frame. You'll end up cutting out a section of damaged cable and assembling it as shown. Although, if I do say so myself, the slight over-exposure makes for quite a nice photo.

Top Of The World

2007-05-10T15:49:00.000-07:00

attic Last weekend I went on a little exploration of my attic. There are two water tanks up there, quite a lot of wooden beams and lots of rockwool insulation. Not all of the rockwool is in the right place, so I've attempted to distribute it properly with a pair of sturdy gloves and a fancy dust mask.

Anthony Axford delivered a batch of quarter-boards of chipboard and some aluminium angle which I've used to board up some of my attic. Using the aluminium angle as guide rails I've been able to put down boards to create useful storage space while still allowing me to lift the boards up in case I need to do any electrical work in the future. The south side of the attic already contained quite a lot of wiring which I couldn't cover in case of overheating, but the north side was free of it so I've been able to create quite a lot of useful space there.

Happily, a quarter sheet of chipboard is exactly the width of the rafters in my attic. I didn't know that would be the case when I ordered them - it could be a coincidence but it's probably something deeply entrenched in ancient building codes that makes things a multiple of one foot sizes.

Tiny memory cards

2007-05-01T16:20:00.000-07:00

microsd 2GB!! On that tiny thing? Crazy. In the gallery I've got pictures of that next to an 8MB Playstation memory cartridge, which is about 100 times the volume. If I could find it, I'd have a picture of my 8" floppy disc drive next to it. Kids these days. Honestly. Tsk.

I've bought this for my new M3 DS Simply cartridge, which promises to allow me to put some homebrew software onto my Nintendo DS. I was introducted to it by a friend at work who has ScummVM working on his DS using the same cartridge, but I'm mainly interested in writing my own software for it. At the moment though, I have no idea what that entails - I'm led to believe the thing has a couple of ARM processors but apart from that I know nothing.

Bed #2

2007-05-01T16:12:00.000-07:00

A few weeks ago I thought it'd be a good idea to make myself a bed rather than buying one. After all, I'd get to make one to my exact specifications and it wouldn't look like anything you could buy from Ikea. In addition, I'd made a bed before and it had served me very well.

The thing is, when I say 'a few weeks ago' I actually mean 'over a year ago' and I've had the timber cluttering up my front room since then, and simultaneously been opposed to buying a proper bed because I'd already made that small initial investment. Since then other commitments kept appearing, such as fences blowing down and my employers who continually expect me to do the job for which I'm paid.

Last weekend I finally finished sawing, chiselling, filing and sanding the components and got the bed assembled, and to be honest it's not that great. My last bed - a bunk bed - creaked quite a bit but I was confident with it because I knew I had enough cross-bracing. The legs on this depend on the quality of the top joints and they're not that accurate, so in engineering terms it's a bit disappointing. Still, it is very solid. I'm mainly glad that all the timber is out of my living room.

Mechanical-digital clock

2007-04-21T14:22:00.000-07:00

mdclock/
I like mechanical digital displays. I had a clock radio with such a display but the existing case was a hideous 50s-style plastic effort, so for a while I've planned on making a new case for it.

While in the pub a few weeks ago, a friend came up with the idea of using copper pipe and plumbing fittings as a structural system. I've started making a frame and it's working out well so far. It'd be nice if they made three way corner plumbing connectors, but I suppose you don't have much call for those when you're connecting up taps.

The biggest challenge in making this is going to be making the mains components safe. There's a transformer for most of the radio, but the clock itself runs off a 250V AC motor. The case will have to be finger-proof and carefully earthed.

Look at the twisted-together connections in the photos of the original radio - they didn't always make things better in the old days.

Toaster modifications

2004-02-23T18:13:00.000-08:00

Every day we are lied to by mainstream media and Hollywood. This is especially apparent in the portrayal of toasters. Toasters in films and cartoons consistently launch hot grilled bread several feet into the air. However, real toasters like the one in your kitchen merely lift the bread by an inch or so after it's grilled. This is very disappointing, and with smaller grilled products, leaves you digging inside an electrical appliance with a spatula to remove your breakfast.

So, one morning I assembled a team to save the world. Omar, Phil and me descended on Winchester to find parts for our prototype.

In the hardware and charity shops of Winchester we found:
* 1 Rowenta TO-18 toaster
* 2 30mm springs

Construction

A brief warning: Do not do this. It involves inserting foreign bits of metal into mains appliances. These are not instructions.

The first job was to remove the original spring, although I kept it in case we wanted to use it in addition to the extra springs. I then clipped the new springs so the end formed a hook shape rather than a ring, and attached it in place of the original one. This gave quite a good improvement in the spring force, but it could be better. Happily, it was quite easy to attach the second spring between two other points on the chassis. The spring still releases without excessive force - this is important, because the toaster could stay on forever if the spring force gets so high it can't release itself.

So, we reassembled the toaster and tried it out without power applied. The first two test items - half a bagel and a slice of stale bread - got a reasonable distance out of the toaster, not quite as high as hoped but as good as we could do, at least until we got new springs. After this, we decided we needed to use an RCD before plugging it in. We didn't have one, so we left it and went to drink beer.

Four months later, I found the toaster in a box I'd used to move house, so went to buy an RCD and try it out.

Results

This time, the results were very pleasing. The picture above was the first take with my camera and the only one needed. Two slices of wholemeal bread on minimum toast setting made it at least three loaf-heights out of the toaster, almost hitting the base of the cupboard. Naturally, it landed nowhere near the toaster, but luckily not on the floor. The toast was tasty.

Robot Wars 2003

2003-08-24T15:02:00.000-07:00

Tuesday 19th August, 5:45PM

Greg: “We’re all sorted. I’m trying to sort out either a Ford pick-up or a Land Rover, but we’ve definitely got a vehicle of some sort.”

Jim: “Great, anything you can find with a decent boot size would be great. I’ll see you on Thursday night, then?”

Greg: “Friday night?”

Jim: “No, Thursday, we need to be in Nottingham on Friday.”

Greg: “Er…”

Cue frantic searching for Robot Wars’ phone number. I’ve got about ten minutes before they close and they’re travelling to the site tomorrow. Luckily, they’re in and are able to reschedule us for 9:30 on Saturday.

Friday 22nd August, 13:00

The weapon is only moving intermittently. With Greg arriving in a few hours, and no idea as to the cause of the problem I’m starting to feel very worried that is going to be a long day.

After a lot of inspection I find the BC108 transistors are getting hot, in fact too hot to touch. These are the first stage of a darlington driver and shouldn’t be handling any current to speak of. The base and collector legs of the transistors are connected via 10k resistors to other parts of the circuit. At 12V, these resistors could conduct a maximum of 1.2mA into each transistor, nowhere near enough to make them overheat.

After checking everything thoroughly the only thing I can think of is that the 12V linear regulator is generating lots of high frequency noise. I solder a capacitor across the output of the linear regulator to smooth it out, and the weapon works perfectly. However, whether I’ve actually fixed it, or that the transistors have just cooled off while I was modifying it remains to be seen. I’m confident enough that the interface will work for long enough to demonstrate the weapon during the tech check, though.

16:00>

Greg arrives with a small tank. Try to put the top armour on the robot which seems to have shrunk. After fifteen minutes of shoving, ratchet compression and hammering, all eight bolts go in. Ish. Set off for Nottingham. It's been three solid days of sawing, drilling and heavy lifting, so sitting in the passenger seat for an unhurried journey down the A6 is very relaxing.

Saturday 23rd August, 7:00

Eat uninspiring but functional breakfast at the hotel and delightedly discover that thieves haven’t broken into the landy and nicked the robot. I have nightmares of finding the robot on sale in the local second hand shop for 50 quid.

9:00 AM

We arrive at the hangar in RAF Newton. I feel somewhat glad that we’re not the only team whose manufacturing skills are not quite up to Razer’s.

Excuse the lack of pictures from here on - I was a bit busy

10:00

Cayene is sitting on the bench in bay 17. Briefly consider taking the top armour off to push one of the drive axle bearings back into place, but think better of it. Manage to push it back into place by sliding a plastic ruler between the wheels and armour.

10:30ish

Tech check performed; passes without any problems.

Time zero: called in

Alan Gribble checks the failsafe works OK. It does, but there’s something not right with the rear right speed controller. The zero area on the controller seems to have shrunk to nothing, so it’s hard to persuade it to stop moving completely, and it seems to be sticking in forward drive when it should be going in reverse.
The front right wheel is working correctly, so on some occasions we seem to have the wheels on the right hand side rotating in opposite directions; going nowhere fast.

T + 10 minutes

Push Cayenne into the loading bay. Realising that the link is on the wrong side, we have to rotate it to put the links in, but it won’t rotate back under its own power due to the same direction problem. Grab one of the spikes and rotate it to face the arena by hand. Drive out into the arena. Get called a tart by one of the tech crew for the message board.

T + 15 minutes

Up in the competitor booth, Cayenne decides to start playing and works perfectly. We drive over to the far corner of the arena and do a few test maneuvers, and spin on the spot a bit to turn the message board to face the judges. No problems. Here goes nothing.

T + 16 minutes

Horn sounds. Drive immediately over to the other side of the arena, so we have our backs to Disconstructor. They follow and we move backwars to ram them, miss them and we end up side by side, trying to turn around each other. We break off and move out halfway down the arena to get enough room to build up for another ram on Disconstructor. But something’s wrong; we’re not moving fast enough, and soon enough we were stopped completely. Frantically shake the controller and transmitter but we’re not going anywhere. Disconstructor move in for the kill and our message board is wiped out instantly (8mm polycarbonate). They circle around and take another swipe at the front of the robot, knocking the crusher jaws back into the frame of the robot, and smack a final hit on the right side of the robot. Cease is called.
The time from us being immobilised to being hit by Disconstructor was very small, so I think the damage they dealt out was fair.

T + 18 minutes

Kim Davies bulldozes Cayenne out of the arena. One of the judges (I think) asks us if we can repair it, which could have meant a discretionary place was on the cards. But from the look of things we’re not going to be running again this week.

A lot later…

Quickly surveying the damage, it doesn’t look like any of the internals have been badly damaged. Two of the rear spikes have been ripped off, the linear actuator’s clevis has been sheared off and one of the chassis beams has been bent, putting the right front axle out of alignment.

We didn’t notice for quite a while that one of Disconstructor’s teeth was still stuck in our armour (highlighted on the picture to the right). Disconstructor said the teeth were such a hard grade of steel that they couldn’t angle grind them, so I considered it quite an achievement that we’d managed to break one of them off. It took a lot of persuasion with a 4lb hammer to remove it.

We had been extremely lucky with the speed controllers. One of our interfaces, which are mounted inside the speed controller enclosure, had been hit and the interface microprocessor was cut clean in half. I’m used to getting segmentation faults in my programs, but not quite this severe. Another inch and they would have cut the speed controller in two. The interface comprises less than ten pounds worth of components, so we had a lucky escape there.

Reasons for the failure…

As far as I could tell both halves of the robot were working fine until we lost power. This means we probably had a ‘common mode failure’ - a fault in the design of each system rather than a random component failure. A gradual reduction in power would be what you’d expect from a flat battery, but all the batteries were still pretty much fully charged - we measured them at about 12.7 volts each after we’d got them home. The most likely culprit I can think of at the moment is the darlington driver circuit which holds the speed controllers’ ignition relays on. The circuit is identical to that used in the weapon interface, which we knew was overheating. On previous tests (when we’d been running for a good five minutes) we were running without the top armour on, so the ventilation would have been much better. This is just theory at the moment, we haven’t had time to retest everything.

Reflection (19th September 2007)

I never did find out what was wrong with that incarnation of Cayenne. Two of the speed controllers were found to be broken; the other two are still in Cayenne to this day and the broken ones were replaced with a RoboteQ controller. I could have done better given an extra day to tune up and debug, but that is always the case. No further series of Robot Wars were filmed, so I never got a chance to have another go. Still, I’m very glad I got to stand in the famous booth with a working robot, if only for a short while. It’s very tempting to give up the night before a fight, when nothing seems to be working and you’re covered in cuts and grazes from rapid, haphazard metalwork.

Disconstructor unfortunately drove into the pit in the first televised round. It was a good robot which could have gone a lot further with better luck, but it would have been nice to get knocked out by someone better recognised.

Cayenne was dismantled after the fight and rebuilt with a completely new chassis as Jalapeno. It went on to fight at Magna and held its own quite well in a one-on-one fight with Tornado at Preston.

LED Message board hacking

2003-04-23T15:33:00.000-07:00

LED message boards look nice, and are much more eye-catching than a LCD or TFT screen. However, proper message boards are expensive - about £150 - so you’d need a good reason to justify buying one.

Maplin occasionally have ‘toy’ message boards on sale much cheaper - around £25. However, these can only hold a short message and this has to be programmed in via a small built-in keyboard. They are not quite so well built as the proper message boards, and have slightly smaller displays, but apart from that they only differ in terms of control electronics.

Under the hood

Maplin’s message board is called a ‘GM Light’. This produces no useful results in Google, other than lots of pages for GM Light Trucks and a pistol of some sort. However, pulling the device apart reveals some more interesting information. There are eight ICs on board. There are five of one sort, which can be easily identified by the part number printed on them. The relevant code is 74HC574, which identifies it as a latch. Two more are 74HC164, a shift register. The remaining chip is oddly packaged, looking like another piece of PCB with a resin blob in the middle where the chip presumably is. There are no markings on it, so presumably it is an ASIC, and its use will remain a mystery.

By tracing some of the tracks on the board, it’s possible to figure out how the board should work.

How it works

The board is divided horizontally into 4 blocks of 16 columns and one block of 8 columns. One of the latch chips drives each of these blocks. One latch chip drives a whole row in each block. The latch chips all share the same data bus, so the latch clock lines must be triggered individually to load different data into each latch.

The shift registers are joined together so that the highest bit output of one shift register is the data input for the second. This effectively daisy-chains both chips, enabling a bit pattern to propagate through them.

From this information I could figure out one way in which the board could work. This may not be the way the ASIC does it, but that doesn’t matter.

By loading a single pulse into the shift register at a time (i.e. 1 every 16 clock cycles), all the outputs of the shift registers will turn on sequentially. Each output from the shift registers is connected to a transistor which, when on, conducts the cathode of each LED to ground. Consequently, one column in each block is activated on each clock cycle. The inital pulse to the shift registers must be regenerated every sixteen cycles.

The latch chips control the rows, so data loaded into them will control the pattern of LEDs seen in the currently activated column. By loading new data into each latch for each new column, a pattern can be displayed. Note that there is no ‘output enable’ (or at least if there is, we didn’t use it) but the latches can be loaded so quickly that any glitch is invisible.

Rewiring

Obviously we can’t write to the latches or shift registers ourselves while the ASIC is trying to do the same, so the ASIC has to go. A more patient person might use a solder pump or wick to unsolder the ASIC from the motherboard, but I went for the brute force and ignorance approach. I jammed a knife under one end of the ASIC and ran a soldering iron down each side of the chip repeatedly until it came away (it’s effectively surface mounted). Unfortunately, some tracks on the board are routed through pads for the ASIC, and my approach ripped a few tracks up, so I had to patch the PCB back together again. The yellow wire on this photo is one of the patch wires.

Once the ASIC was gone, the remaining rather fiddly job was to attach wires to the appropriate chip pins - 7 to the latch data lines, one to each latch’s clock line, one to the first shift register’s data line, and one to the shift registers’ clock.

It’s then a relatively simple job to hook up all the lines to a PIC16F871. I put all the lines through a 1k resistor to avoid damage due to contention - although all the lines should be inputs to the message board PCB, there might be something else on there driving a line that I hadn’t noticed.

Programming

The next step was programming the PIC16F871 to drive the appropriate lines. The code to multiplex the display has to run quickly to maintain a reasonable image, so I allocated a ’screen buffer’ to hold the current pattern for the LEDs. With one byte for each of the five 16-column blocks, this is 80 bytes - a lot for a PIC16F871 which has very limited on-board RAM. This leaves only 16 bytes free in the main page. Actually, the display only uses 7 bits of each byte, and the last half of the fifth byte is invisible (off the edge of the display) but it makes the software much simpler to consider it as an 80*8 bit array. In fact, the eight columns which are invisible are useful - they can be used as an offscreen buffer to download the next character into.

Once the code to display a multiplexed pattern is done, the next stage is to make the pattern change. The two important jobs are to scroll the display (simple) and to insert new characters into the pattern (difficult). Scrolling just involves running through the buffer and copying each location to the location further down. This happens much more slowly than the multiplexing code.

To insert new characters, we need to know what the next character should be, and also what bitmap makes up this character. The font is held in the PIC16F871’s program memory. Program memory is much more plentiful on the 16F871 than RAM, but requires some memory-mapped IO in order to retrieve it. There is a slight time penalty, but this isn’t so important as a new character only needs to be fetched infrequently, with respect to the speed that multiplexing occurs.

Getting all the timing and character downloading right took a long time, but eventually I had a scrolling message on the display. This was the majority of the work for version 1.0.

Version 1.0

Version 1.0 of the message board had a message hard-coded into program memory. I loaded it with an insulting message, and attached the whole board to the back of my combat robot, Cayenne

Unfortunately, I don’t have any pictures of Cayenne with the message board attached. A couple of days later, I took Cayenne to the qualifying sessions for Robot Wars 7. There is never enough time to do what you want at a robot combat event, and taking photos is a fairly low priority. There are, however, several pictures of Cayenne with the bits of the message board that were swept out of the arena after the fight.

Version 1.1

Once my enthusiasm returned, I thought of another use for a message board.

Using several ‘talkers’ (chat rooms) on a laptop with a small display poses a problem - how to keep track of all the messages arriving from several sources at once, especially when you’re working on something that requires the full display. Sure, you can make each terminal beep when it receives a message, but you still don’t know which window it came from, or if it’s important enough to switch away from your main application.

So, why not get all the messages from your talkers displayed on a scrolling LED display? To do this, I added serial communication to the original display, so it would display any text sent to the serial port of a PC. The PIC16F871 has a serial port on board, but it only works on TTL voltage levels. Help comes in the shape of the wonderful MAX232 chip, which generates the +/- 12V required by RS232 from a 5V source.

Serial communications

Cunningly, I initially wired it up in TX-TX and RX-RX configuration. Luckily, I used my £10 laptop for testing and the MAX232 chip didn’t explode, so after a bit of debugging I swapped it for the more conventional TX-RX, RX-TX configuration and connected it to my server. Now, my server could talk to the message board.

I implemented a 16-byte rolling buffer on the 16F871 - the only memory available on the chip - and got it to send XON/XOFF bytes to stop the server sending too much data at once. There were a lot of problems with the buffer - mostly due to my own incompetency, assigning two variables to the same address, and not preserving variables in the serial recieve interrupt routine. Debugging was tricky as Microchip’s MPLAB can’t simulate the serial port. However, after a few irritating nights, the message board worked as planned.

From the talker to the display

In order to use talkers as normal, I use the unix tee command to split off output. For example,

telnet example.org 8080 | tee -a example.log

Then a separate process runs tail -n 0 -f example.log > /dev/ttyS0 - having set up ttyS0 for 300 baud communication with xon/xoff flow control. Why 300 baud? That’s the speed my robots’ radio control system runs at, and I copied the code directly from the receiver. 300 baud is still faster than the message board can cope with.

This displays everything coming through the talker on the message board. Of course, it would be better to filter this. I currently have a sed script to remove ANSI codes, and this could be expanded to check for interesting messages (new message posted, user login etc)