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For a project in progress, I have an Arduino UNO sending a message when a condition occurs, and a Raspberry Pi that listens to it. Both are fitted with NRF24L01+ modules with antennas.

It works perfectly when the Arduino is powered from a wall socket, for instance using a 9V / 1A power supply. But when I try it with a 9V battery (which is supposed to supply 600 mAh), the Raspberry Pi receives only 1/10 of the messages.

Could you tell me:

  1. Why this happens
  2. How I can solve this problem (software / wiring / capacitor / ...)
  3. What would be the best way to power an Arduino whose only job is to detect that a switch closes, and emit a message over the air

Here is the code of the emitter (Arduino). And there is the code of the receiver (Raspberry Pi).

Thank you.

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    600mAh is capacity, not current. – Ignacio Vazquez-Abrams Mar 22 '15 at 17:31
  • 4 rechargeable AA batteries (4 x 1.2V)(bypassing the voltage regulator). Note that you will probably only get a few days of usage out of batteries, because you are using an UNO, since the USB-to-Serial chip doesn't sleep. – Gerben Mar 22 '15 at 17:49
  • Actually I think I should be able to use just two AA batteries. I was just testing the design on the UNO. It's really not a low power device... The regulator sucks a lot of current, and there is the power LED. So it's probably using most of the juice of the 9V battery already, doing nothing. – tiktak Mar 24 '15 at 15:47
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According to the datasheet of another 9V battery, I should not expect more than 30 - 50 mA of constant current. This is probably the reason why.

Long story made short: One can not power a NRFL01+ reliably with a 9V battery. I'd be better off using 2xAA batteries.

  • According to my measurements, the Uno would take 50 mA from a 9 V battery. You are already at the upper end of the range you quoted. Now power up a transmitter and the voltage probably drops so low it fails. One can not power a NRFL01+ reliably with a 9V battery - more like, "One can not power a Uno reliably with a 9V battery". – Nick Gammon Jul 28 '15 at 4:50
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    I'd be better off using 2xAA batteries. - why not 3xAA batteries? That's only 4.5 volts. Put it straight onto the 5 V pin. – Nick Gammon Jul 28 '15 at 4:50
  • Does anyone have idea/guess, for how long it will run on 3xAA batteries ? – Bhushan Oct 19 '16 at 7:39
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Another thing to consider is that a nrf24l01+ chip at full power will potentially be pulling more current than your 5v reg can supply, try a lower power setting on the PA.

  • This is exactly the opposite. NRF24L01+ draws maximum 14mA of current. Arduino Uno board draws much much more. – Avamander Aug 17 '15 at 23:03
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Add a 100uf capacitor between ground and 3.3v directly on the nrf breakout. They're very susceptible to noise on the power supply. I had issues with the same thing and this solved it. Also, make sure you're powering from 3.3v. Also make sure you solder the negative to the negative!

see capacitor placement

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