Wednesday, 19 March 2008

Load Average Meter



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.

3 comments:

DJGibbon said...

Surely the next stage is a flashing red light-in-a-cage for when load gets too high?

David said...

Love this, been wanting to do something similar with my slug to show network load. Can you give any links to the maplin usb interface?

I was thinking about just using a small usb audio out device (they're just 4 quid on ebay) to drive a vu meter but not really sure if that would work to be honest.

Great blog. I've added you to my rss reader

srimech said...

David, the interface board is this one http://www.maplin.co.uk/Module.aspx?ModuleNo=42857&DOY=13 - it was on sale at £20 assembled when I was in the shop (amusingly, still £30 unassembled).

I think running a VU meter from an audio output would work quite well, actually. It might need more complicated software on the PC though.