Simple AVR ISP programmer

My first AVR programmer was just a parallel port cable with few resistors. It worked like a charm.

I would like to have few simple AVR ISP programmers, but the parallel port isn't present in modern computers. I decided to design similarly simple programmer with USB-C port. CH551G is great microcontroller for this kind of applications, as it only needs couple of passives when creating USB gadgets.

Feature for me, but could be problem for you

The programmer circuit shown in this video is as simple as it gets. It supplies the target with 5V power coming from USB. For my use, 5V always wired to the VCC pin is fine, as most of my AVR circuits are designed to be powered from 5V.

Components

WCH CH551G does all the heavy lifting. Resistors and two decoupling capacitors are 0603 size, USB-C jack is the very common 16 pin type, with four through hole mounting tabs.

Firmware

I ended up using firmware from this Stefan "wagiminator" Wagner's repo. Due to differences in hardware, I had to edit the pin settings in src/config.h, changing the PIN_RESET value from P14 to P31:

https://github.com/wagiminator/AVR-Programmer/tree/master/picoISP_Programmer/software/picoisp

With that firmware, the programmer shows up as USBTinyISP, which is supported in Arduino IDE for programming the bootloader to Arduino boards. I needed to install libusb-drivers for the programmer using Zadig:

https://zadig.akeo.ie/

Video: What, why and how