I started this project because I often use USB-C chargers in my maker builds. They are compact, powerful, and everywhere. But I quickly realized one big limitation: I had no clear way to measure what was really going on.

• Which voltage profile did the charger negotiate?
• How much current was actually flowing?
• Was the power stable over time?

Commercial USB-C testers exist, but most are closed-source and not easily hackable. So I decided to make my own tools.

In the end, I built two different devices:

• The OLED Power Meter – simple, compact, and with instant readout of voltage, current, and power.
• The Wi-Fi PD Logger – no display, but logs data for hours and serves live plots in a browser.

Both share the same core: a PCB with USB-C connectors, a shunt resistor, and an INA219 measurement chip. The Power Meter is based on an STM32 microcontroller, while the Logger uses an ESP-01s with Wi-Fi.

What surprised me the most was how quickly these tools became part of my everyday bench setup. I use the Power Meter when I just want a quick look, and the Logger when I want to study a charger’s behavior over time.

All the resources are available in the GitHub repository: schematics, PCB files, firmware, and 3D-printable cases. If you’ve got a USB-C charger and a 3D printer, you can build your own too.

Next, I’ll add some detailed build logs with photos and sketches from the design process. Stay tuned!