I'm trying reverse-engineer a circuit on an espresso machine water boiler. I was looking at this post: Water Sensing Circuit
which seems to be essentially the same idea. Really the only differences are:
*I'm only working with one probe. The other "probe" is actually just the surface of the boiler, which is grounded. I've measured roughly 2Mohms across the probe and ground when water is touching it.
*I'm trying to run low voltage AC instead of DC, to avoid corrosion. The original circuit produces a square wave at 1kHz, 3.6V Peak to Peak. I figured I could easily produce a similar signal with a microcontroller and circuit similar to: Changing a Signal's DC Offset
Is there an AC equivalent to a circuit controlled by a PNP transistor?
Best Answer
Add a blocking capacitor with a weak bias (high value resistor) to system GND on the output side. This will produce an AC waveform centered about GND.