Update 2024/11/13: V2 revision: smaller, breadboardable and upgradeable, and more manufacturable!

The USB-Cthrough helps you tap into USB-C Power Delivery and EPR (high-voltage) communications, DisplayPort, proprietary protocols, and even Thunderbolt negotiations without any issues! It's featureful, USB-C standard compliant, upgradeable, designed and tested for high-speed interface use.

How Does It Work?

The USB Cthrough lets you tap into a PD or an SBU connection between two USB-C devices, intercept PD negotiations, reverse-engineer proprietary PD-based or SBU-based standards, tap into reserved USB-C pins on phones and laptops, toy around with the USB-PD protocol, and even debug or stress-test your own PD devices if you set out to build one.

To use the Cthrough, you plug it into one of the USB-C devices, between the device and the cable. It works with any kind of USB-C device out there - no exceptions! Because it's a plug-socket board, it's also compliant to the USB-C standard, so the board works in either polarity and doesn't impede on any of the USB-C aspects like Vconn. Unlike other similar boards on the market, this is a 6-layer board, with the high-speed signals impedance-matched and laid out with care (tested working up to Thunderbolt 4 speeds!). All the user-exposed signals are nicely marked on the board's silkscreen, and the headers are positioned to work on a breadboard, making for an easy-to-install PD debugging setup.

After you've plugged this board in, you can immediately probe your signals of interest with a multimeter, or, make use of the numerous features this board has to offer! For a start, this board has jumper headers for CC and SBU pins, so you can do MITM - these headers are joined with traces by default so that the Cthrough is ready to use without soldering, but these traces are easy to cut if you want to inject your own data. In fact, you can use tin snips or flush cutters to break these traces in a pinch - the board has gaps in the copper so that you can avoid damage to other traces while you cut! Afterwards, if you need to reconnect the traces, you can simply solder a pin header into the holes and plug in a jumper, or quickly make a solder jumper with your soldering iron instead.

If USB-C power is what you're looking at, it also has a microcontroller-friendly output for measuring VBUS - a resistor divider that divides the VBUS voltage by 11, bringing it into range for any 3.3V microcontroller's ADC. Non-divided VBUS signal is also available, and you can draw about 1A (pin header limit) from it in a pinch.

What's more - if you want to also monitor your USB-C device's power consumption, you're in luck! There's a current shunt inserted into the VBUS connection, which lets you use a current shunt amplifier to monitor your device's power consumption. The shunt is 0.01ohm, center tapped as per Analog Devices recommendation, and you can install a different value shunt with a hot air gun if desired.

The v2 version has added 2.54mm-grid-aligned pin headers. With those, you can make "addon" modules for the Cthrough - for instance, a logic analyzer adapter, a power meter compliant for DisplayPort use, or a MITM setup for PD retransmission.

In Summary

Last but not least - the PCB design is open-source and can be found on Github! This is a very powerful debugging tool for USB-C PD development, reverse-engineering and debugging, and I'm glad I can finally offer this to you.