SRJM.co.uk » Electronics

Project Update

Simon — Wed, 20 May 2009 21:50:22 +0000

A typical picture update of the project from both aspects, the 3D and the physical interface.

Digital Atmosphere

Terrain Spikes

Testing the spike generator for visual feedback on the terrain:

Pulse Rate Sensor

Sensor in the Handle

Electronics

Simon — Tue, 12 May 2009 21:16:11 +0000

Although I’m still waiting to find out if the PCB I requested a week ago is ready I have been able to get on with trying to produce the remaining electronics.

I’ve found out that the Analogue-to-Digital-Converter of my USB board is pretty sensitive and simply connecting my circuits resulted in extreme noise rather than a smooth stable reading. So in order to solve this I’ve placed some beefier 1uF (rather than the 0.1uF on my GSR circuit) capacitors between the output and the ground which seems to stabilise it perfectly.

Powerful LEDs

Hopefully they will illuminate the centre of my handle, which now has acrylic beads glued into the holes in order to catch the light. I took this photo with my light on, not in the dark…

Thermistor Circuit

Note the purple capacitor across the thermistor. Without it the circuit gives out a perfectly stable current, but the ADC doesn’t seem to think so.

Power Socket

After soldering my socket onto a small piece of board (with the intention of simply attaching the other circuits’ power wires) I thought that maybe I should do a diode bridge to ensure polarity. Hence it was a challenge but I nicked the diodes from a broken AC to DC transformer and managed to fit them onto the board with enough room for soldering the wires on the end. Now it doesn’t matter which way around you connect the power :)

Wheatstone Bridge

Simon — Thu, 23 Apr 2009 17:08:18 +0000

A possible means of measuring a specific resistance of an unknown component, skin for instance is to use a Wheatstone Bridge. Basically by measuring current across the centre of the bridge, and comparing the difference between one side which is a known value, the resistance of the unknown component can be obtained. If the unknown and known resistances were the same, then a current of 0V would flow through the centre.

http://en.wikipedia.org/wiki/Wheatstone_bridge

Hunt for GSR Measurement

Simon — Mon, 20 Apr 2009 08:18:20 +0000

My hunt for circuit schematics has obviously been ongoing for a while but I hadn’t really discovered much worthwhile until lately. Eventually I came across an excellently documented electronics project for producing a polygraph, one measurement of which it is taking is Galvanic Skin Response:

http://courses.cit.cornell.edu/ee476/FinalProjects/s2007/jsc59_ecl37/jsc59_ecl37/report2.html