How can I get my (Arduino) Pro Micro schematic to allow me to program it through GPIO instead of USB

Question

I'm trying this project so far I've got the schematic of a Pro Micro, which is powered through GPIO from a Raspberry Pi Zero, and want to remove the micro usb connection and able to flash it using an avr programer and a few pins.

How do I get to Achieve that? also the Pro Micro is getting D+/D- from the the raspberry's D+/D- pads as well. Schematic below for reference. enter image description here

• Pararera: Yes, you can program Pro Micro with programmer.
• jsotola: you cannot power the board through GPIO pins ... those are for input/output only
• Juraj: if Micro is connected to PI with USB, you can use it for serial upload to Micro from PI with avrdude.
• Juraj: I would like to understand what you want to build. PI has GPIO so why to attach a Micro?
• per1234: Please provide an explanation of what you mean by this: "flash it using an avr programer and a few pins", and why you want to do that.

Answer 1

Welcome to arduino.stackexchange.
You can program your ATmega32U4 on at least two ways:
1. Use Arduino's bootloader and D+/D- pins. This way you won't need an external programmer. Try search for phase "programming ATmega32U4 with bootloader".
2. Use ISP (In-System-Programming) method. In this case you can use your avr programmer. To do so you also need access to PINs named Reset, MISO, MOSI, SCLK. See this link or this one

As always, the important read is ATMega32U4 datasheet.

• m1gu3: Awesome, links and everything. Thanks a lot!

Answer 2

Why don't you buy a pi zero to USB add-on board? You can stack the pi on top and plug it into a normal female USB port on your computer.

The USB board has some pins that connect to the solder points of the mini USB, so you can delete all the connectors you won't need.

Other option is to solder a wire to the pi and extend the connector with a cable.

I'm not shire, if you can program the pi true its serial pins. USB is a serial connection after all. So I think this should be possible

• m1gu3: Hey @DAM, your idea sounds very doable but the main concept of this project is to have a mobile rPi, I want to flatten it most I can. But thanks for your input I might use some of those ideas too!

Answer 3

An avr programmer uses the ISP interface to program a chip. For this you need the pins for MOSI, MISO, SCK and Reset. Of course you have also to provide power to the board through Vcc and ground.

I'm not sure, if it's OK to keep the USB connection while programming via ISP, but since you want to remove that connection either way, this isn't a problem for you. You can remove the USB connection completely (no D+ or D- connection).

Note: when you are programming the Arduino Micro via ISP without also burning the bootloader, you won't be able to use USB for programming anymore, until you burn the bootloader again.

• m1gu3: Sounds good, so basically a 4 pin header with MOSI, MISO, SCK and RST will do the trick. And yeah its exchanging data with the rPI without the USB plug I guess. Sorry not an expert on this kind of things, thanks!
• chrisl: Depending in the voltage, that the Micro runs on, you may need a level shifter, so that nothing gets damaged due to too high voltage