I recently purchased a 5V arduino pro mini that I now wish to connect to a BLE device.

I firstly tried the BLE device with my Uno board and it worked very well! However when I now try to use it on my mini it does not start.

This is my wiring: First I connect the pro mini to the uno in order to upload the code looking like this:

  1. Arduino Mini Pro to Arduino Uno

  2. RX --> TX

  3. TX --> RX
  4. VCC --> 5v
  5. GND --> GND
  6. RST --> RST

Then I wire the mini to my BLE device (https://learn.adafruit.com/getting-started-with-the-nrf8001-bluefruit-le-breakout/hooking-everything-up):

  1. Arduino Mini Pro to BLE nRF8001

  2. 13 --> SCK

  3. 12 --> MISO
  4. 11 --> MOSI
  5. 10 --> REQ
  6. 9 --> RST
  7. 2 --> RDY
  8. GND --> GND
  9. VCC --> VIN

When I connect this setup to the computer the arduino uno starts and also the pro mini (both has LED lights on). I upload a simple test code that worked when i tried it with the uno but the BLE device does not respond (it seems like it does not turn on) when i use it with the pro mini.

Any idea what might be wrong? I have my board put as: Arduino Pro or Pro Mini, ATmega328 (5V, 16 MHz).

Thanks a ton!! :)

1 Answer 1


This is my wiring: First I connect the pro mini to the uno in order to upload the code looking like this:

Arduino Mini Pro to Arduino Uno

RX --> TX
TX --> RX
VCC --> 5v

How would this work? The bootloader in the Uno and Mini Pro will both try to reply. You need a FTDI or a USB-to-UART module instead of the Uno. Alternatively, start by programming the Uno to act as a USB-to-UART converter using Serial and SoftwareSerial.


  • I saw the connection from this thread: instructables.com/id/SpeechVoice-Controlled-Arduino-Drone/… Check under "Step 1". I also found this thread that has similiar connection: instructables.com/id/…
    – Martman
    Mar 26, 2017 at 18:47
  • But maybe it will not work to use the Uno as a "code-uploader". I have this at home also: youtube.com/watch?v=59VHCXNxSvQ Check minute 1.56. I have the red one. Would that work with the Pro mini?
    – Martman
    Mar 26, 2017 at 18:50
  • The second link is fine. The MCU on the Arduino Uno is removed and the board is used as a USB-to-UART. The first link is an SMD AVR MCU and the trick might be the 3.3V setting. The Mini Pro is using 5V. Mar 26, 2017 at 18:53
  • Ah ok. I do not have a big MCU/Atmel on my current arduino (i got a chinese copy) and i assume it will be hard to remove it. Did you see the youtube-video, do you think that could work with the pro mini to upload code? It has GND, RXD, TXD and VDD pins
    – Martman
    Mar 26, 2017 at 18:56
  • 1
    Yes, the Arduino IDE setting should be the target board. In this case the Pro Mini. Check frequency (8 or 16 MHz) and voltage (3.3V or 5V). Mar 26, 2017 at 19:28

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