Do you want a trigger board for your project, but one that works exactly the way you want? Do you want a USB-C adapter that fast charges your phone but also makes it work as a data host? Do you want to build a USB-PD tester or sniffer, but one that's more flexible than any of the available ones on the market? Do you want to get DisplayPort out of your USB-C laptop while also charging it, with all the custom behaviour you might want? Do you want to reuse USB-C peripherals with older devices, or perhaps add a USB-C port to your not-as-modern laptop? Reverse-engineer USB-C peripherals? Any other project where you want to speak USB-C PD? I've designed the Altmode Friend for all of these goals, and more.

The Altmode Friend module:

• couples a RP2040 with a FUSB302 in a handsoldering-friendly footprint
• is a self-sufficient USB-PD device, fully tested in a variety of PD applications
• has example code in MicroPython for a large amount of PD scenarios
• easy to hack on if you want it to do more than USB PD
• exposes a large number of RP2040 GPIOs, including the ADC ports, as well as SPI, I2C and UART peripherals
• can work as the main MCU for your project
• is breadboard-friendly for all your prototyping needs
• is fully open-source and easy to add to your KiCad boards

This small friendly module will help you in your USB-C PD pursuits! It's self-sufficient for all your PD negotiation needs and more, super flexible and small, letting you add a ton of external hardware to your project - you can even use this module as your project's main MCU. You don't need a separate chip with a very specific purpose to talk a limited amount of PD in your projects anymore - just put this castellated module onto your PCB or breadboard, connect the CC pins to your USB-C port, tweak the module's software if needed, and have it talk PD for you - with any kinds of custom behaviour you could want. What's more, this RP2040 exposes enough GPIOs that it could easily be the main MCU for your project!

PPS voltage extraction

Software

The Altmode Friend has an RP2040 paired with a FUSB302B USB-PD frontend, and I provide a MicroPython interface so that you can implement your own behaviour by writing Python code. My goal is to let you talk PD from a comfortable MicroPython environment with GPIOs aplenty, adding as much custom behaviour as your projects need.

Here's the code I've created so far:

• A USB-C PD tester for reading USB-C PSU profiles
• A sink that requests static voltage and the amount of current you choose (improved trigger board behaviour)
• A sink that requests voltage based on the power capability of the charger
• A PPS sink that requests variable voltage and current
• A DisplayPort sink that helps you extract voltage out of the USB-C port
• A USB-C PD sniffer that decodes PD and VDM (i.e. DisplayPort) packets

Again, everything is fully open-source, and the code is well-structured and documented. I'm currently working on custom USB-PD power supply code - stay tuned!

If you ever need help hacking on this code, let me know - I'd be glad to help. If you're reasonably experienced and looking for a mature stack in a low-level language, you can also already use this module to talk USB-PD by using one of the openly available USB-PD stacks; there's quite a few - the IronOS stack, a stack from MicroChip, and even one for Arduino.

Sniffing USB-C packets using the Altmode Friend

Why Is This Awesome?

I've listed quite a few usecases for module, that you can't achieve with typical PD stuff available for sale, such as trigger boards and pre-made devboards. In general, with this module, you can do anything with a USB-C port - get custom voltages and currents, sink or source, use alternate modes like USB3 and DisplayPort, and tap into proprietary or debug features. You can also create a USB-C port that provides anything you'd like! It's perfect for use in larger project where you want a separate PD controller so that your main MCU or the CPU can free up some resources and avoid any software bringup conflicts with the hardware requirements. So, if you're building a custom motherboard with USB-C, feel free to use this module as a dedicated USB-C peripheral, as it can free you up from a lot of USB-C worries. And, of course, you can use it as a trigger board - it's hardly more expensive than one, and significantly more fully-featured whenever you run into limitations, like trigger boards simply picking the highest voltage available, or not communicating the supported current levels to you.

A custom board using the Altmode Friend as the main MCU and the PD controller

There are large benefits to a separate and configurable module for USB PD, whether you compare it to trigger chips or wiring up a PD PHY to your main MCU. It's a standalone part of your project that can easily integrate into other parts, and the RP2040 can also act as the main MCU for your goals if the project's small enough. It also lets you easily create custom PD behaviour, like powering a device of yours only after a proper voltage and current have been negotiated, or controlling high-speed signal switches without getting your main CPU involved. In fact, your main CPU doesn't have to be awake, especially if getting it awake is a catch-22 without PD - this module can negotiate any voltage or altmode your CPU could need before it boots up. I've been creating highly featured PD-chatting gadgets with these modules, and if you too want to harness the power of USB-C ports around us, this module is a perfect fit.

Need PCB designs for inspiration, or for KiCad symbols/footprints/3D files? The example design is the devboard you can use for inspiration or add to your PCB order, already fully tested - it has KiCad symbols and footprints. Second example design is the Framework laptop mainboard replacement project that turns the Framework laptop chassis into a KVM - the design is currently WIP, but files are already available.

As usual, I've packed this module with as many features as could fit while keeping it easy to work with - let's go through them!

Hardware Features

• Seriously small - 18x18mm. PCB is 1.6mm thick, but next revision will be thinner.
• The castellated pads make it easy to hand-solder and reflow.
• The silkscreen on the back shows all GPIOs, as well as the FUSB302B connection information (I2C port and INT pins).
• It's self-sufficient - bring your own 3.3V and a USB-C port, but not much else is needed!
• 2MB flash by default - more than enough for MicroPython and tons of custom code, while keeping the PCB thin.
• It's breadboard-able! Two rows of pads on opposite sides have all the vital features and a few GPIOs handy - side pins aren't crucial to the module's operation, they're mostly extra GPIOs. When plugged in, this module leaves two rows free from each side on a standard breadboard, which will be plenty for your jumpers, resistors and wires.
• As a result, this module is also protoboard-able for your less-than-permanent projects - all the pins are on the 2.54mm grid!
• There's a whole lot of RP2040 GPIOs exposed, including GP0/1 for UART0, two ADCs, and enough pins to do SPI or extra I2C if you ever need that.
• There's a third ADC connected to VBUS through a resistor divider, clamped with a 3.6V Zener diode for protection.
• The BOOT pin is exposed on one of the ADC pins through a 0R jumper (populated by default), in case you ever need to use it for flashing.
• VCONN is jumpered to the module's 3.3V input by default. You have to remove the VCONN jumper on the module if you want to supply external VCONN!
• The hardware is designed to support EPR up to 28V.

Using the devboard to build DisplayPort sink communication code

Devboard Features

There's a power-application-intended devboard available for use with the Altmode Friend! It's a PCB with a protoboard space, two USB-C ports and power management, that an Altmode Friend solders onto. It's intended as a devboard for the Altmode Friend as much as it's intended to be a reference design. Most of all, this board is a USB-C playground!

Of course, the devboard is also packed with features!

• Two USB-C ports - one is connected to the Altmode Friend's CC pins, and other has 5.1K pulldowns for 5V/3A mode. You can use one port for CC communications with a PSU, hub or other device, and another for programming, experimenting and monitoring your code's behaviour!
• Is only 46x46mm, and wastes no space, with a 1.6mm thick PCB.
• Has a prototyping space which supports a large amount of SMD and THT components, with THT pads on 2.54mm (0.1") grid and SMD pads on 1.27mm (0.05") grid, supporting SMD packages like SOT23 and SO- packaged ICs, if you ever need those!
• All the GPIOs are broken out to the prototyping space edge pads, silkscreened onboard, available on top and bottom layers. You can easily add buttons, LEDs, power switches, DC-DCs, and whatever else you could desire.
• There's a 3.3V switching regulator onboard, with up to 2A output, available for powering other onboard devices. As you can guess, that's quite overkill for RP2040 purposes, and it can easily power one-two Raspberry Pi Zeros or a WWAN modem without breaking a sweat. The next revision might have a less powerful regulator, but in the meantime, I hope this one can be of help!
• This board's hardware, including the regulator, is also designed to support EPR up to 28V!
• You can power this devboard from either of the USB-C ports - no compromises. Also, both power inputs can be disconnected with a jumper, and you can remove/shift the jumper if you ever need that.
• You can wire up the RP2040's USB data lines to either of the two USB-C ports - whichever fits your application better! You only need to shift two jumpers for that.
• The prototyping space has ground lines available on the bottom, letting you wire up ground to your components easily by adding solder jumpers.
• You can supply VCONN externally if need be - it's jumpered to 3.3V by default, but if that doesn't work for you, you can go higher. You need to remove both the jumper on this devboard and on the module if you want to supply external VCONN to the module!
• All pads are ENIG (gold-plated), for great soldering experience and long shelf-life, ready whenever you might need to do some PD experiments!
• If you ever want to experiment with DisplayPort, AUX pins are exposed on both ports, so that you can test initial stages of DisplayPort negotiation before you design a custom board with high-speed lanes.

Building a USB-C PSU platform using the devboard's prototyping space

The Altmode Friend can be used as a building block of your own board, or it can be used standalone, or perhaps, copy-pasted wholesale as the PD heart of your new design. Whichever path you take, I hope this module helps you on your journey!

This is a fully open-source product! Use the "Design files" link below to get the KiCad files for your own research.