The project originally stems from my CH32 tutorial series. I started working with this chip not so long ago and started to create projects and tutorials so that more people can get access to well-explained resources. During the tutorial series, I discovered the ADC of the CH32V003F4P6 chip and I also wrote a custom library to drive different OLED displays. When I was working on the ADC-related tutorial, I generated the voltage to be measured by the ADC of the microcontroller via a potentiometer. To confirm the measured voltage by the ADC, I used one of my multimeters. It was a bit cumbersome because of the wires and the lack of space on my computer desk. Then it occurred to me that it would be nice to have a tiny voltmeter that I can have directly in the breadboard.

This shifted my attention to the CH32V003J4M6 microcontroller which is an 8-pin microcontroller. It can be considered as the “direct competitor” of the ATtiny85 microcontroller. However, the CH32 is somewhat more powerful, so maybe we cannot really talk about direct competition. :) Also, to go down in size as much as possible, I selected a 0.42”, 72x40 pixel OLED display for this project. The PCB for the circuit is only 12 mm wide and 24 mm long, so it is tiny. So the whole circuit only takes up 4 rows of space from a breadboard. Its minimal occupancy becomes even more apparent when the board is used in “standing mode”.