I just got a 5V Arduino Pro Micro, which I connected to an RC RX powered from the VCC and GND pins of the board.

However, whenever I do so and power on the board from a computer USB connection or a wall adapter USB connection, the board goes into an odd mode where the red RX and TX leds flash rapidly (~0.5s on and ~0.5s off) and USB serial ceases functionality. (presumably, because the MCU isn't on anymore)

If I remove the load and power the board again, everything works as normal.

This is an odd behavior, especially since I read online that the VCC pin is rated for ~150ma max and my device (FS-iA6b) isn't a very high power device, tested by me to draw 30-50ma max.

What is happening here? I haven't even connected the 5v signal pin yet!

  • It would help if you included a schematic. It sounds like your receiver is drawing too much power. Are you powering the micro from the USB port or from the RAW pin? Try powering the micro using the RAW pin with a 4xAA battery pack. Commented Nov 7, 2018 at 14:03
  • @JeffWahaus I'm not really sure how to upload a schematic, it's a relatively simple set of interconnects: RC RX 5v VCC pin connected to Pro Micro VCC pin, RC RX GND pin connected to Pro Micro GND.
    – ifconfig
    Commented Nov 7, 2018 at 16:49
  • I've been trying to avoid adding an external power source if I can avoid it. The Arduino Uno had enough power on it to power the RC RX...
    – ifconfig
    Commented Nov 7, 2018 at 16:50
  • A standard USB port should be able to supply up to 500mA, it seems like either something is shorted or perhaps you have a 3.3V version of the Pro Micro. Commented Nov 7, 2018 at 17:40
  • Wouldn't the 4-6v RC RX not power on if the Pro Micro was 3.3v? It does power on.
    – ifconfig
    Commented Nov 7, 2018 at 18:34

1 Answer 1


Aah, I figured it out! @JeffWahaus was correct, the RC RX was placing too great a strain on the Arduino Pro Micro. My latest working theory is that when the RC RX is in communication with the RC TX, it has current spikes that allow the system current draw to exceed that required to drop the voltage coming out of the 5V regulator below that required to shut off the ATmega32U4 MCU.

The solution I found, upon recommendation, was to move the RC RX voltage source from the VCC pin to the RAW pin which taps power from ahead of the 5V regulator and add a 10uf capacitor in parallel with the RC RX to smooth out any current spikes.


simulate this circuit – Schematic created using CircuitLab

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