USB C-thru

Open USB Type-C/PD Probe

Mar 07, 2016

Project update 2 of 5

Demo #2: Explore Google Chromium USB Type-C example designs using USB C-thru

Google is one of the early adopters of USB Type-C and USB Power Delivery in their Chromium projects. Interestingly, Google shared the complete design of the USB Type-C products in the public domain, from the schematic to source code of their implementations. This article explores how to use USB C-Thru board to explore Google’s designs, thereby helping you to develop custom design of your own.

This article shows you how to make your own Google USB-PD Sniffer, a.k.a. “Twinkie”, using the USB C-Thru and a STM32 development board ($65.00 USD) in three steps.

Hardware requirements:

  1. USB C-Thru

  2. STM32F072B development kit

Step 1: Preparing software and firmware binary for Google’s USB PD Sniffer

Figure 1: List of USB Type-C design examples from Chromium website

Step 2: Setting up Hardware STM32F072B-DISCO with USB C-thru

Now that you’ve set up the necessary software and flashed the board with firmware, let’s explore how to set up the hardware to build a Twinkie.

Figure 2: Schematic of Twinkie indicating CC pins
Figure 3: Schematic of Twinkie indicating CC pins

This setup gives you enough of the Twinkie functionality to act as a USB PD sniffer.

Step 3: Start sniffing USB PD data with homemade sniffer

With the USB C-thru board and the STM32 discovery board set up and connected, the sniffer is ready to deploy for debugging. In the example setup, we are using a laptop with a USB Type-C charger and USB-C Thru-based sniffer connected to an Ubuntu PC.

Figure 4: Enumeration of STM32 development board as Twinkie device
Figure 5: Google’s USB Type-C example design Twinkie implementation using USB C-thru and STM32


This article provided a quick walk-through of how to use USB C-Thru board with an existing development kit, demonstrating how to make your own USB Type-C experimental design. You can explore other Chromium USB Type-C design examples in similar manner with a few wire wrapped electronics.

In the next article we will provide test results of USB C-Thru from 3rd party labs.

Order your USB C-thru today, and feel free to write us for any clarification at

Sign up to receive future updates for USB C-thru.

Subscribe to the Crowd Supply newsletter, highlighting the latest creators and projects