I had built a simple static field detector before, that would turn on an LED when a comb or a piece of cellophane was brought near its antenna; but I was able to enhance the sensitivity of the circuit using a PICAXE microprocessor. The basic circuit centers around a FET (field-effect transistor) with a long wire on the gate as the static electrical probe. The FET's drain to source current changes in response to minute changes in the gate voltage, and since it is high impedance, it won't drain away static fields. The FET's drain is connected to the ADC (analog to digital converter) of the microprocessor where it is represented by a number between 0 and 255 (8-bits). Through observation in debug mode I set a high sensitivity threshold at 60 and a low sensitivity level at 100. When the static energy exceeds these levels, a brief chirp sounds from the piezo speaker (not loud enough to disturb my wife) and the LED turns on. This little system can detect a charged comb (just run it through you hair) from a meter away. I tried it last night, and it only went off once; at 3:04AM! I am quite pleased with this result. Whatever is bugging me in the 300AM hour is detectable and generates a static field. For a few dollars in parts I might build a bunch of them and distribute them around the house.
The circuit diagram [Link]
The BASIC code [Link]
The parts list [Link]
My other interests [Link]
The first week, it went off twice, both times right at 3:00AM (no other times during the night). The next 2 weeks no alarms. Then a cold front came through, and the air is so dry that the static is so high the unit is in constant alarm. I need to change the code to self-calibrate for changing humidity levels.
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