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Disable external module to preserve battery life

jonnyfishman last edited by

Second question for the evening. I have tried several versions of the circuit below to disable an external RFID module when it is not needed (it is triggered by a button press).

The left circuit it the standard one for an RFID module but I have tried to disable it using a BC548 NPN transistor and D4 pin set to LOW when not in use (right circuit), but I can't get it to stop being powered. The LED responds as expected and turns on an off depending on D4's state but the RFID module always seems to be powered. Is this likely to be because of its other pins MISO etc, or because D4 isn't setup properly.

N.b. I have tried without the transistor and the module remains powered regardless of D4's state.

Thanks in advance,
Jon
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hello, i know it is late, but others could see it too. i had the same problem running small (LOW POWER) modules on power banks, because the battery or power bank has a built in power meter, while it is charging and consuming power, there will be power on the USB port, but the arduino's consumption is very tiny regarding charging a phone. you need to disable this feature somehow.
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