Read if voltage on external line is on or off with esp12e

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Re: Read if voltage on external line is on or off with esp12

By donbrew
- Fri Jan 08, 2021 3:41 pm #90127 Why over engineer? Just use an automotive 12V relay with 3.3 volts on the switch. If the 12V source fails the the 3.3V or ground will go either high or low depending on if you choose N.O. or N.C.

Usually we think of a relay using the lower voltage/current to switch the higher voltage/current, but it works the other way too.
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