Saturday, 14-02-2004

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The sensor, ready for testing The test circuit

Using a junior hacksaw, i isolated the sensor unit from the other circuitry in the tyre pressure gauge.
The test circuit allows the air pressure to be read, and resistance values across the sensor to be taken.
Whilst testing the sensor, i also recorded the air muscle's size at different air pressures.

At 2 psi the resistance across the sensor is 1000 ohms. At 11 psi, 70 ohms. At 22 psi, 45 ohms. At 33 psi, 28 ohms.
The resistance values are too small to be directly useable by the RCX, and with my very limited knowlegde of electronics, a way of making the values useable is beyond me...


Ok... i was testing the wrong part of the sensor... it seems like i was testing the resistance across the auto-on switch... doh!

I been doing some research into air pressure sensors, the one i'm using is about the same a most commercial units... in the picture above, you can see a small chip on the board... this is a silicon pressure sensor... it's resistance changes with pressure.

Again, the values across the chip are too small to be directly used by the RCX, 2 to 35 psi resulting in a very small voltage drop across the range.

To make the pressure sensor useable, will require additional circuitry... more research!

To have a pressure sensor inside each air muscle would give good feedback as to the length of the muscle, as the air pressure in the muscle directly relates to it's size.

A cheaper and simpler method of providing feedback about the size of the air muscle could be to have a potentiometer built into the joint of whatever the air muscle is moving. Using a pot for the position of the joint would mean 1 sensor per pair of muscles.

I also have an idea for an electronic inline air valve, just waiting on a few tiny neodymium disc magnets from Neo Magnet Emporium and construction will commence!

And this weekend i'm going to try to build an LTD stirling engine... and get some more platinum medals on Project Gotham Racing 2... wifey and kids are away til Monday :)

Party on!!!


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This page is part of a diary of the design and build of my Lego Mindstorms robot J5 (based on Johnny Five from the film short Circuit.)
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