I thought that maybe putting a DC-blocking capacitor in series with the battery might allow me to make some sort of brief measurement at the instant that somebody touched the sensor by using some sort of capacitive sensing. Any ideas?
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leon_heller wrote:Microchip has application notes on using standard PICs for touch sensor applications. If you need an MCU you might as well do it that way. You need a couple of metal pads covered with plastic, IIRC.I've read their app notes on creating capacitive sensors, but unfortunately this seems to be a special case. The way they did it, I would end up shorting two voltage sources together, which is not a good thing to do. The only way to use their app notes is to isolate the supply voltage of the battery, but still somehow read the capacitance across it (which is why I had thought of maybe putting a DC-blocking cap in series with the battery).
You'll still need something to be at the other end of the e-field that the user is disturbing.The answer there would be to provide capacitive coupling from the touch-sensor circuit to the battery. I wouldn't think that the touch-sensing would be ground-referenced per-se. So I think my original suggestion is likely all it takes (at least on paper).
saipan59 wrote:I just thought of an idea that has a "chance" of working:Wouldn't this have problems if your draw from the battery isn't fairly constant? If you've got digital circuitry it's going to have sudden changes in current demand from the battery, and the inductors would impede that. I'm not sure how much of a problem it might be, but it's something to keep in mind.
Put an inductor in series with each side of the battery, then connect a capacitor from the exposed side of the battery to the touch circuit (whatever that may be).
In theory, the inductors allow the battery to supply DC power to the circuit normally. Yet for AC signals (such as the touch circuit), the battery appears to be connected to 'nothing'.
Let me know if this scheme actually works...
saipan59 wrote:There are capacitive sensing transducers in the market.You'll still need something to be at the other end of the e-field that the user is disturbing.The answer there would be to provide capacitive coupling from the touch-sensor circuit to the battery. I wouldn't think that the touch-sensing would be ground-referenced per-se. So I think my original suggestion is likely all it takes (at least on paper).
Quantum Technologies Tech Support Guy wrote:Hi Brennen,I was actually wanting to use the QProx chips because the uC I'm working with is really small and doesn't have very many I/O pins. I may still try the circuit that Microchip uses in their docs but have the supporting hardware external to the microcontroller, just to see if i can get anything going.
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The electrode can be made of any conductive material but it must not have a potential on it. It needs to be a conductor just connected to the sensor. So I’m afraid your idea will not work.
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