Thor Forums

[FW28z]

Originally Posted by JamieGeek

My plan is to use a one-shot to power the circuit off of the house battery when it detects power on the sense wire. The one shot will power the circuit for approx 10 seconds. Even if the tank is "full" (e.g. the circuit "grounds" all of the sense wires) the timer in the one shot will still provide power for the 10 seconds.
This way the regulator on the Arduino won't be seeing 12V all the time (and thus not be consuming current). At the moment I'm estimating the circuit to consume less than 20ma while active and am looking for a one-shot that consumes ~0ma when not triggered.

Not a bad idea.

I was thinking of something like an opto isolator that could sense the sense wire voltage. When dormant, there is no voltage on the sense wire, so the opto isolator would be off. But when it sees voltage, the output of the opto isolator could be on the ground side of the capacitive circuit, which basically turns it on like a switch.

But it might be tricky to keep the led side of the opto isolator from pulling down the sense voltage.

The output of the capacitive circuit could also be an opto isolator, but the MOSFET type (typically called an electronic relay). But depending on the current going through the LED, you should be able to vary the "resistance" on the output side (which is connected to the sense line). Other options might be a programmable or voltage controlled resistor.

These days there are so many cool special purpose integrated circuits that most anything is possible.

On the other hand, a one-shot circuit would work very well, and I like it's simplicity... simple is always good. Even if the delay was much more than 10sec, it would not significantly discharge the coach battery.