[SOLVED] Pro Mini 3.3 Voltage supply issue

  • Hi,
    I have an issue I'm struggling with and I'm looking for any suggestion to try to find out a solution.

    I'm trying to develop a relay like version of mysensor using the following:

    • arduino pro mini clone 3,3V 8Mhz
    • NRF24L01+

    the sensor communicates with another microcontroller board (no arduino) already running for several months through 2 digital pin configured as input and output to get or set a status; of course I have the electronic part in order to convert levels between the systems.

    I'd like to share the same 12V regulated power unit I'm using to power the no arduino system using the RAW pin; through the Vcc pins I'll power the radio module and give a fix reference for the other system open collector output.

    I'm not able to understand which regulator uses my pro-mini, I can see printed out on the case something like A20I, but since I read that most of the clones uses the LP2981 I was confident I could supply until 16V, but when I connect my pro-mini everything works for not more than 1 hour, the pro-min stops to work and after some investigation I can see that the mini -pro regulator is broken. I already fried two regulators. I checked the power unit voltage output and I have values around 12.04 / 12.08V.
    Do you thing the pro-mini clone regulator cannot manage 12V? Or it cannot supply the current requested from the radio module (but it should be around 15mA anyway)? Is it better to use an external voltage regulator to get 3,3V from the 12V or I could have the same issue and get fried also that one?
    Thank you in advance for any suggestion or idea.

  • Hero Member

    @mortommy in most cases 12 is the max for a clone pro mini. When you have a relay attached to the same power supply the induction gives transients on the powerline which a way above the 12v.

    I would suggest a separate regulator for the sensitive device (ie 7805) with sufficient decoupling between ground and positive voltages.

  • Thank you @AWI . So with the 12V I'm on the limit edge...
    I'm not using physically a relay but a transistor based circuit connected to the digital output.

  • Hero Member

    @mortommy Yes 12V is max. even for the "original" pro mini. Switching any inductive (coil) or capacitive (capacitor) load gives transients. Usually you can use a suppressor (i.e. zener diode) to protect your circuit. In this case you could try (12.1V) but it would be very near to the maximum voltage. Many clones use cheaper components (i.e. 10v SMD capacitors) which are below specification.


  • Hardware Contributor

    I've been running an APM 3.3V clone as a repeater for over a year at ~15V without issues. Only unusual is the non-switched supply with just a transformer, rectifier and filter. Don't know if it matters.

  • Hero Member

    @m26872 you are lucky 😉

  • Mod

    @m26872 said:


    Did you measure this voltage under load, or just on the unconnected outputs of the transformer?

  • This post is deleted!

  • Hardware Contributor

    @Yveaux Don't remember, I'll have to double check.

  • With an external regulator it has been running already for 24h 🙂
    thank you.