Closing in on a final circuit:
The left side is the circuitry used for the sensor wire; the right side is the circuit used to measure the tank level.
R6, R7, and Q4 will be used to wake up the Arduino. When the button is pressed on the panel that will allow some current through R6 turning on Q4 grounding the wakeup pin (Putting the Arduino to sleep should draw less than 2ma--at least it was when I measured it earlier). I don't really know the size of R6 yet: I want it to be large enough that the current through Q4 is enough to wake up the Arduino but small enough that it doesn't affect the measurement.
Q1-Q3 are used to "simulate" the sensor probes to the panel. When all three are off (logic low on PD2-PD4) the tank will indicate "Empty". Turning on PD4 should signal "1/3" full, turning on PD3 should indicate "2/3" full and turning on PD2 should indicate "full". I figured it would probably be easier to just put all the resistors here and only connect 1 signal wire than connecting each probe's wire to the board.
SW1 is used to wake up the circuit when standing next to the tank (instead of having to run inside and press the button). Having the button here implies that I'll also have a display showing the level. That circuit isn't on the diagram...yet.
Thor Forums
