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NRF24L01+ seems very sensitive to electric noise

Vidar Kristiansen

Hi

I am working on a design using an nRF24L01+ in a circuit also consisting of an ATMEGA microcontroller and a H-bridge motor driver driving a brushed DC motor. The whole circuit will be battery powered.

Now, the nRF24L01+ seems very sensitive to electric noise produced by the motor.

As a consequence the nRF24L01+ seems to crash and needs a reset by cutting the power and switching it back on. The ATMEGA microcontroller of the circuit seems to be far less sensitive and takes this noise well without crashing.

As for the noise from the sparks produced by the commutator of the brushed DC-motor, I have found that it can be successfully filtered away using three 100nF capacitors on the motor, one between the terminals of the motor, and one between each terminal and the motor casing, as well as a reasonably large capasitor, 100µF, on the 3.3 V power supplied to the nRF24L01+.

But I have another problem also. I mentioned that the circuit will be battery powered. Everything works fine when the batteries are fully charged.

But, the nRF24L01+ does not seem to like it much when the batteries are starting to run a little low and the motor is switched on. Because the change in voltage due to running the motor is also something that sometimes seem to crash the nRF24L01+

Contrary to what I expected when measuring the supply voltage to the nRF24L01+ when running the motor on a battery that is a little out of charge, the voltage across the power terminals of the nRF24L01+ does not drop, but actually jump up a little. I assume this is due to the 3.3 V linear voltage regulator that I am currently using, overcompensates for the drop in battery voltage.

When I run the system on batteries that are fully charged the voltage from the regulator stays constant when the motor runs.

So, I guess that a clue here is to find another 3.3V voltage regulator that does a better job suppling the nRF24L01+ with a more stable voltage even in the situation that the batteries are a little low on charge and a larger load is switched on.

Question 1: Do any of you, from experience, have any voltage regulators, that would do a good job doing so, to recommend

Question 2: It would be nice, for an added degree of robustness, if the microcontroller could wake up the nRF24L01+ in the event that the latter has crashed. Does anyone have a word of advice as to how that might be accomplished?

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    Some ideas:

    1. Use a watchdog timer.
    2. Output a square wave from the nRF and detect it from the Atmega to check for liveness.
    3. Add a larger smoothing capacitor for the motor. 300 nF is not very much for a motor.
    4. Add another capacitor for the nRF after the regulator (do you have one)?
    5. Run the nRF from a separate battery to see what causes the problem exactly.

    I've used Sparkfun's 3.3V step-up regulator for powering an nRF51822 from 2xAA batteries and it works fine.

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  • 0

    Some ideas:

    1. Use a watchdog timer.
    2. Output a square wave from the nRF and detect it from the Atmega to check for liveness.
    3. Add a larger smoothing capacitor for the motor. 300 nF is not very much for a motor.
    4. Add another capacitor for the nRF after the regulator (do you have one)?
    5. Run the nRF from a separate battery to see what causes the problem exactly.

    I've used Sparkfun's 3.3V step-up regulator for powering an nRF51822 from 2xAA batteries and it works fine.

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