Make Your Own USB-C Power Delivery Tools: OLED Power Meter + Wi-Fi Logger

I built two DIY tools that let any maker explore USB-C Power Delivery (PD) in a practical way:

1. a small Power Meter with an OLED display that shows voltage, current, and power in real time, and
2. a Wi-Fi Logger that records these values over hours and displays interactive plots in a web browser.

I created them because I am using USB-C chargers in my projects, but I had no easy way to measure what was really happening. For the “Build a Tool” contest, I wanted to design something useful, reproducible, and open source—so that anyone can turn an ordinary USB-C charger into a versatile lab tool.

All design files, schematics, PCB production data, 3D-printable cases, and firmware are available in the GitHub repository.

USB-C chargers are everywhere today—phones, tablets, and laptops all rely on them. They can deliver up to 100 watts, making them powerful enough to serve as flexible power sources for maker projects.

But there’s a problem: as a maker, I had no simple way to see what was really happening on the USB-C Power Delivery lines. How much voltage and current is the charger actually negotiating? How stable is the power over time?

That’s why I designed my own tools for the “Build a Tool” contest. My goal was to turn an ordinary USB-C charger into something you can actually measure, monitor, and trust in the lab—without expensive test equipment.

USB-C Power Delivery (PD) is more than just a charging standard. It allows devices and chargers to negotiate the right voltage and current for each situation. With profiles from 5V up to 20V and power levels up to 100W, the same charger can safely power a phone, a tablet, or even a laptop.

For makers, this means a USB-C charger can serve as a flexible lab power source. Instead of keeping multiple power supplies on the bench, one small adapter can cover many needs—if you have the right tools to control and measure it.

To request a specific voltage, you need a small controller chip. A great example is the CH224K, which makes voltage negotiation simple. With a chip like this, you can easily turn any USB-C PD charger into a compact adjustable power supply.

Projects like the Hackaday CH224K USB PD Decoy provide excellent inspiration and ready-to-use breakout boards for prototyping.

To explore USB-C Power Delivery, I designed two complementary tools. They serve the same purpose—measuring voltage, current, and power—but in different ways:

1. The Power Meter
2. A compact device with an OLED display that immediately shows voltage, current, and power values. Just plug it between a USB-C charger and your device, and the numbers appear on screen. It’s perfect if you want quick, real-time feedback.
3. The PD Logger
4. A headless device without a display, but with Wi-Fi connectivity. Once plugged in, it serves a small webpage where you can view live values from any browser on your network. Even better, it logs data for hours and provides interactive plots of voltage, current, and power over time. This makes it ideal for analyzing stability and long-term behavior.

Both devices are easy to use—just place them between the charger and the load, and they do the rest. Once powered, the PD Logger joins your local Wi-Fi network and can be reached in a browser under the hostname pd-logger.local (or alternatively via its IP address, e.g. http://192.168.0.xxx).

Depending on your needs, you can choose the quick-read Power Meter or the long-term, browser-based PD Logger.

Both devices share a similar structure: a main PCB, a small board carrying the male USB-C plug, and a 3D-printed case. The cases were designed in Fusion 360 and can be printed on any standard FDM printer.

1. PCBs
2. The production data (Gerber files) are included in the GitHub repository. You can order the boards from services like JLCPCB, but of course other PCB manufacturers will also work.
3. Electronics
4. For both devices, the male USB-C plug board is connected to the main PCB using a 6-pin angled header. This provides both electrical connectivity and mechanical stability.
5. In the Power Meter, the OLED display is then soldered directly to the main PCB.
6. In the PD Logger, the ESP-01s Wi-Fi module is soldered in place.
7. Cases
8. Each device has a three-part case (top, bottom, and insert). The Fusion 360 design files are included, and the STL files are ready to print. During printing, you can pause at the right layer to embed four small nuts (M2) into the case, which allow the device to be closed with screws (M2x10).

With these components—PCB, parts, and a 3D-printed case—you have everything needed to assemble either tool.

Both devices run custom firmware that you can build and upload with PlatformIO inside Visual Studio Code (VS Code). All source code and configuration files are available in the GitHub repository.

1. Power Meter (STM32)
2. The Power Meter uses an STM32 microcontroller. To flash it, you’ll need an ST-Link adapter. A dedicated programming header on the PCB allows you to connect the ST-Link, even when the microcontroller is already soldered in place. Once connected, simply open the project in PlatformIO and run the Upload task.
3. PD Logger (ESP-01s)
4. The PD Logger uses an ESP-01s Wi-Fi module. You can flash it with a common ESP-01 programmer. Similar to the Power Meter, a header on the board provides easy access for programming.
5. One important detail: while flashing, the ESP-01s must also be powered. Plug the PD Logger into a USB-C charger, and connect a load to the output so that Power Delivery negotiation starts. Only then will the device be fully powered for programming.
6. In addition to uploading the firmware, you must also upload the web interface files into the ESP’s LittleFS storage. PlatformIO provides a task for this (usually Upload Filesystem Image). Without this step, the built-in web server will not display correctly.

With these two small devices, I now have the missing tools to really see what’s going on with USB-C Power Delivery. The OLED Power Meter is great for quick checks, while the Wi-Fi PD Logger shines when you want to record data for hours and analyze trends in your browser.

Both tools are compact, affordable, and open source. All design files—schematics, PCB layouts, 3D-printable cases, and firmware—are freely available in the GitHub repository. This makes it easy for anyone to reproduce, adapt, or extend the design.

I built them for the “Build a Tool” contest, but more importantly, they’ve become part of my own maker toolbox. Now, instead of guessing what my USB-C chargers are doing, I can measure and log the details with confidence.

I hope this inspires you to try it out yourself, and maybe even improve or extend the project. If you do, I’d love to see your builds!