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WeightSensors  
Weight sensor circuit information.
Updated Feb 4, 2010

Circuit

We were originally going to use an op-amp, but because we only need three states (nothing, empty bed, occupied bed) we can use a more crude system. We will use the weight sensors - which are simply variable resistors - as voltage dividers, similar to the circuit shown in figure 32 here but without the op-amp. I tested some values using one of the chairs in the lab and a resistor value of 500kOhms seems best - it gives a few mV for no load, 1-2V for just the chair, and about 4V for the chair with me in it. These ranges are quite clearly separable.

Code

I've made a C function that returns whether or not the alarm should be active, given lower and upper thresholds (which are determined by calibration). The code is currently in the wttest project.

Comment by mhaniff...@gmail.com, Apr 16, 2011

sdsd

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