This project realizes a tiny "self-sufficient" power meter that can be inserted into any DC power line thanks to its small footprint.

The PCB utilizes the INA238 high-precision power meter chip and the circuit is managed by an ATtiny85 microcontroller.

The circuit can be powered either by an external 5 V source or it can be powered directly from the monitored power line (never both at the same time!). Between 3.8-32 V, the device is "self-sufficient", so it can be powered from the monitored line. In this case, the jumper pin (or holes) on the right side of the "R5" text must be shorted together. This connects the bus voltage to the input of the buck converter.

If the expected voltage is outside of this range, the device must be powered from the external 5 V pin. In this case, the jumper or short must be removed so the buck converter only receives power from the external 5 V source.

The input voltage is then stepped down to 3.3 V by the onboard buck converter (AP63203). All the onboard components are powered by the buck converter, so all the digital components are at 3.3 V.

The holes at the corners act as connectors. They are M4 pads. I used some binding post terminals, but if a larger display is used, a spade connector or ring terminal is recommended.

Please check the attached BOM (Excel file) and interactive BOM (HTML file) to see all the necessary parts. Also, check my video and my blog article for more information.

Update 2023-08-22:

• I added a few new pictures to the gallery showing the device with three different displays.
• I added the links to the new video and blog article where I explain the improvements for this board.