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I'm using a Pro-Micro to send messages using NRF24 module from a remote location, using batteries (later on, will be recharged using solar panel).

To conserve power, Pro-Micro wakes up every 30 minutes, sends its data. My goal is to power up NRF24 module only when needed, in order to conserve power as much as possible.

For that I tried 3 ways:

  1. Using a Relay to cut off 5V input to the NRF24 module.

  2. Using a MOSFET FQP30N06 , connected to GND of NRF24 module.

  3. Using NRF24's powerDown() function reduce consumption.

These are the current draw results:

a) During sleep, power consumption of Pro-Micro only is 3.4 mA ( due to LED remains ON ).

b) Pro-Micro + NRF24 module, both normal operation ~70mA.

c) Using a relay + entering Pro-Micro to Sleep mode: 6mA.

d) Using powerDown() + entering Pro-Micro to Sleep mode: 30mA.

e) Using a MOSFET + entering Pro-Micro to Sleep mode: 180mA. (yes, MOSFET turns off power to NRF24 ).

Questions:

** I have to say that my first go was for using a MOSFET, but I was amazed by the result! What is the reason for that? Can it be the when MOSFET in its OFF state consumes so much power ?

** I would like to hear from other's experience for better ways to do such.

Guy

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    No, MOSFET does not power off the whole NRF when it only switches the GND. There are other connections like e.g. the SPI pins that can act as grounds when they are low. Feb 9 at 15:12
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    For switching the power for such a device, you should use a high side switch, meaning a P channel MOSFET for switching Vcc.
    – chrisl
    Feb 9 at 15:19
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    Those 70mA and 30mA look way too high to high to me. I was able to run my setup on an average of around 0.5mA, with the MCU waking up every 250µs to do a measurement and occasionally sending data via the NRF24. Putting the NRF24 in power-down mode should be sufficient bring it's power usage to almost nothing. It might be a counterfeit NRF24L01. Is the chip on your module a QFN chip, or is it under a blob of epoxy?
    – Gerben
    Feb 9 at 15:32
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    In that case, those values sound a lot more plausible. Those have an additional amplifier, so they will probably use more power. The power adapter boards have a linear regulator, which has around 5mA of quiescent current.
    – Gerben
    Feb 9 at 16:37
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    @Guy.D you can't set SPI pins to LOW. You have to disable SPI first, before you can change them.
    – Gerben
    Feb 9 at 16:39

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