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I have 2 Arduino UNO R3 nodes communicating using NRF24L01+ transceivers with the TMRh20 library.

Setup I have original as well as cheaper but 'compatible' arduinos. One of the nodes uses an original arduino Uno whereas the other uses the cheaper one.

Observation

  1. The node with the cheaper Uno can transmit data (sucessfully received by the other node) but is unable to receive data. I have a number of Rf modules and UNo boards. The observation is similar across.

  2. Using the same configuration (rf module, connection and code) , the original uno board receives data but noot the other types.

  3. Another thing that i observed is that the cheaper uno comes with a 12MHz oscillator on the board whereas the original one has a 16 Mhz one.Can it be the source of problem?

This article mentions something that I could not get but am suspicious of it being a possible direction to the solution to the problem, only if someone could help.

On Arduino UNO boards SPI pins are connected with some digital pins. While using modem you most remember that these digital pins won't be available.

  • The code was taken from here arduino-info.wikispaces.com/Nrf24L01-2.4GHz-ExampleSketches#bm1 – sherinkapotein Nov 1 '16 at 10:48
  • Another thing that i observed is that the cheaper uno comes with a 12MHz oscillator on the board whereas the original one has a 16 Mhz one.Can it be the source of problem? - Big silver can? That's for the USB interface only. 16MHz for an ATMega16U2 (or whatever, I can never remember the silly numbers) and 12MHz for a CH340. – Majenko Nov 1 '16 at 10:51
  • Although having read that somewhere already, not quiet sure if that wouldn't affect the SPI or anything to do with my setup, hence brought it out again. Thanks – sherinkapotein Nov 1 '16 at 10:56
  • No, that crystal has no connection to the main MCU at all. – Majenko Nov 1 '16 at 10:56
  • @Majenko: Thanks. any insight on anything other that might help me with my problem. – sherinkapotein Nov 1 '16 at 11:10
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As it turns out, the culprit was the power supply on the board.

The clone came with AMS1117 based regulator for the 3.3V which it did indeed generate (3.27 measured). Using it, the reception of the RF device failed (although it could transmit data). Also had 10uF and a 0.1uF capacitor hooked up in parallel to Vdd and Gnd of the NRF24L01+, as recommended. I therefore suspected something to do with the SPI configuration.

Finally, having powered the 3.3V to the Rf device from another genuine Arduino solved the problem. Not sure if it was the 3.3V rail from the clone possibly having excessive noise which may be causing the issue, as I did not see a reasonable drop in 3.3V output of the clone while in operation.

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