Upload to board with no USB connection

Question

I have a Spark Fun Pro Micro (ATmega32U4) without a USB connection (it was broken off at an earlier point) that I want to use to duplicate a prototype running on another Pro Micro.

How can I upload a sketch to an Arduino without a USB connection?

Answer 1

The best solution is to solder back the connector or to buy a new board.

Ways to use a board with ATmega32u4 without USB for development are:

• ICSP programming
• upload over a serial bootloader.

Both require additional hardware.

For ICSP upload you need a programmer device. After configuring it, select the programmer in Tools menu and you can use "Upload using programmer" from the sketch menu. It is even possible to create a custom board definition which will use "Upload using programmer" with the "Upload" button from the toolbar.

To make serial upload possible you will need and USB-to-TTL-Serial adapter and Optiboot compiled for the 32u4. To burn the bootloader you will need an ICSP programmer or a second Arduino to use with the Arduino as ISP sketch.

Answer 2

Use a programmer, such as one based on CH341A that has pins broken out for CLK, CS, MOSI, MIOS [sic], GND, 3.3V, and connected those to pins on the Pro Micro as follows:

Programmer Pro Micro
CLK-----------15 (SCK)
CS------------RST
MOSI----------16 (MOSI)
MIOS----------14 (MISO)
GND-----------GND
3.3V----------RAW

It doesn't appear that the programmer is supported in the Arduino IDE, so I grabbed chavrprog.

And ran the command $ sudo ./chavrprog -d mega32u4 -a s ~/Arduino/test/test.ino.leonardo.hex

• Juraj: I see. The upload program implements the protocol. This is a very nonstandard solution for the problem in the question.