Quote:
Originally Posted by CTWV50
Ahh I see! You are quite brilliant. One question though! Why does the piezo buzz if a circuit isn't made to the negative side of the battery?  |
Quote:
Originally Posted by twinturbo
Only if the ignition switch changes from live to ground , most will change from live to unconnected not ground.
TT
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Ah ha, you've both discovered the slightly dubious subtlety in my scheme
It's correct that IGN is typically switched from battery to unconnected.
However, there are going to be several things on the car that are powered off IGN.
These will be connected between IGN and GND, and effectively drag IGN down to GND when it's switched off.
The buzzer will sort of leech current through these loads, which is the dubious part. However it requires so little current that it gets away with it...