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I've recently received an Arduino Pro Mini as a gift, and I don't have an external USB programmer to program the Pro Mini. However, I do own an Arduino Uno R3, and I think it would be possible because they both have the same clock speed and micro-controller (16Mhz with an atmega328).

Is it possible to program an Arduino Pro Mini using an Arduino Uno? If yes, how does one do so?

  • Which Pro Mini is it, 3.3V or 5V? I guess this must be the 5V one as I think the other one (3.3V) works only at 8MHz. – jfpoilpret Feb 16 '14 at 9:58
  • I use this method for my Leonardo.. forum.arduino.cc/… – user841 Mar 27 '14 at 23:11
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Just hook up the pins (RX, TX, reset, Power, and Ground) to the corresponding pins on your Uno.

You may have to take the ATMega328 out of your Uno for this to work.

Keep in mind that you need to hook it up to the correct power pin! If your pro mini is running at 3.3v then you must hook it up to the 3.3 pin on your Uno.

Check out the ArduinoToBreadboard page for a bit more info. Scroll down to "Uploading Using an Arduino Board". Although it shows you how to program an Arduino on a breadboard, the wiring is the same.

  • You should remove the ATmega328 from the board. There is a vague chance that it would work without doing so, but chances are even if it superficially worked, you would get errors. – Cybergibbons Feb 15 '14 at 8:11
  • I've gotten it to work consistently as I have the SMD uno. Had to manually reset, though. – sachleen Feb 15 '14 at 18:05
  • This one did not work for me. – Phil L. Feb 1 '15 at 2:17
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you can program with an SMD board, you dont link the reset line, hold down the reset on the uno throughout the whole process, and tap the reset on the mini soon as the ide says upload to upload the sketch, by holding the uno in reset it doesn't interfere with the serial comms

  • Worked like a charm. I kept pressing on RESET for the whole duration of uploading, from before plugging Arduino until having finished uploading. Works great. Thanks a lot. – Phil L. Feb 1 '15 at 2:17
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There is another method by which you can upload your sketch programs. Program the UNO with the "Arduino as ISP" sketch and connect the pro mini via the SPI pins (plus reset line). See "Upload with Programmer" on the Arduino website and elsewhere on the internet including stack exchange. This method will allow you to use the full memory of the chip and avoid using the bootloader, but you will need to upload with SPI each time.

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