A common method used to prevent a dead battery is to visually indicate that the master switch was left on by leaving the strobe switch turned on. The shortcoming with this method in N724CZ is that the strobes and non-essential equipment is powered through the VPX and that gets it's power when the master switch is on.
The nose gear actuator gets its power from the essential buss, so when the nose needs to be raised or lowered on the ramp, the essential buss switch needs to be on.
I don't want the warning buzzer going off when I'm preparing to start or shut down the engine so my logic is:
If a fuel pump is running, don't buzz. The pump makes enough sound, it's obvious a buss is energized.
If the fuel pump(s) aren't running and essential buss is energized then buzz. Either we're preparing to start or momentarily lowering or raising the nose.
To simplify the logic, the buzzer will be powered by the essential buss. Then two inputs are needed that sense if either fuel pump is energized.
www.homemade-circuits.com/how-to-make-logic-gates-using-transistors/The NOR gate in the article above will work with the A & B inputs connected to the positive posts of each fuel pump. The buzzer circuit's ground will connect to output "C" and the positive source for the buzzer will connect to the essential buss.
It might be nice to have a 15 second mute button. The points where a battery charger are connected will need to be on the source side of the master or buss relays to avoid energizing the buzzer.
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