Build a dongle from a XIAO ESP32-S3.
The Printercow dongle is not for sale yet. Its firmware runs on a Seeed Studio XIAO ESP32-S3, the board Printercow is developed on. Flash it from your browser, add a powered USB-C OTG adapter, and it works like the dongle: the same setup, MCP tools, recipes and signed updates.
What you need.
- Seeed Studio XIAO ESP32-S3
- The plain board (8 MB flash, 8 MB PSRAM) and the Wi-Fi antenna that comes with it. Other ESP32-S3 boards are not supported.
- A powered USB-C OTG adapter
- A USB-C plug for the XIAO, a socket for your device and a USB-C socket for power. Tested with the IVIVTOR USB-C OTG adapter (1-to-2 splitter, USB-A 2.0 socket, PD charging port); others sold as "USB-C OTG adapter with charging" should work if they pass power through. The XIAO cannot power its own USB port, so your device gets its 5 V from here.
- A USB-C charger
- 5 V and at least 2 A. It powers the XIAO and the device together.
- A cable for your device
- For most printers, USB-A to USB-B. One device per dongle, no hubs.
- A computer, once
- Chrome or Edge on Windows, Mac, Linux or ChromeOS, and a USB-C data cable, to flash the firmware.
Five steps.
- 01
Fit the antenna
Press the antenna that came with the XIAO onto its U.FL connector until it clicks. Without it, Wi-Fi and Bluetooth barely work.
- 02
Flash the firmware
Plug the XIAO into your computer and install Printercow from the flash page in Chrome or Edge. It takes about a minute.
OPEN THE FLASH PAGE → - 03
Put it on Wi-Fi
Create a workspace, then choose Add dongle on the Dongles page. While the LED blinks slowly, the browser finds the XIAO over Bluetooth and sends it your 2.4 GHz Wi-Fi.
SET UP A DONGLE → - 04
Plug in your device
Unplug the XIAO from the computer. Plug the OTG adapter into the XIAO, the charger into the adapter's power socket, and your device into the adapter. The dongle page shows the device a moment later.
- 05
Connect your AI
Add the MCP URL from the Connect page to Claude or any MCP client and ask it to print. It works out the commands and proposes a recipe for you to approve.
How it differs from the dongle.
| XIAO ESP32-S3 | Printercow dongle | |
|---|---|---|
| Power for the device | From the OTG adapter, straight from the charger | Built in, switched on when a device is plugged in |
| Protection | None | About 1 A limit on the device port, ESD protection on both ports |
| Status lights | One LED | Green status LED and red fault LED |
| Sensor slots | Two pads; you add a 47 kΩ pull-up to each | Two 3.5 mm jacks with power for the sensor |
| Logs over USB | Stop once the board is online | Over the power cable, always |
| Case | None | Printed case with tips that lock on |
| MCP tools, recipes, REST, updates | Same | Same |
Reading the board.
The XIAO has one LED for Printercow and two buttons: B (BOOT) and R (RESET). Hold B for 3 seconds to put it back into setup mode, or 10 seconds to forget its Wi-Fi and workspace.
- Slow blink
- Waiting for setup over Bluetooth.
- Quick blink
- Joining Wi-Fi, signing in to your workspace or reconnecting.
- Steady on
- Online.
- Rapid flicker
- Setup failed. Hold B for 3 seconds and set it up again.
Sensor slots.
Slot 1 is pad D0 and slot 2 is pad D1. Solder a 47 kΩ resistor from each pad you use to 3V3, then wire a switch or a sensor output between the pad and GND. Keep signals between 0 and 3.3 V: the XIAO's pins do not take 5 V. Recipes read the pads exactly like the dongle's jacks.
When something does not show up.
The browser lists no serial port.
Use a data cable; many USB-C cables only charge. If the port still does not show, hold B (BOOT) while you plug the XIAO in: it starts in download mode, which always shows up. Press R (RESET) after the install. On Linux, your user needs to be in the dialout group.
The XIAO already runs Printercow and the computer does not see it.
Once it is online, the XIAO hands its only USB port to your device. Hold B while you plug it in, then install. Leave Erase device off to keep its Wi-Fi and workspace. Updates normally arrive over Wi-Fi anyway.
Setup does not find the XIAO.
Hold B for 3 seconds until the LED blinks slowly: the XIAO advertises itself over Bluetooth again. Setup needs Chrome or Edge on a computer or an Android phone; browsers on iPhone cannot use Bluetooth.
The dongle page shows no device.
Your device needs 5 V from the OTG adapter. Check that the charger is in the adapter's power socket. If the device or the XIAO stays dark, the adapter does not pass power through; try another one.
I want to start over.
Hold B for 10 seconds. The XIAO forgets its Wi-Fi and its workspace and restarts in setup mode.
How do updates work?
New firmware is offered on the dongle's page and installs over Wi-Fi. Every update is signed, and the XIAO only accepts builds made for the XIAO.
Its limits.
- There is no current limit on the device port: a short in the device or its cable goes straight to the charger. Use a charger with its own protection, and devices that draw at most 1 A from USB or have their own power supply.
- There is no case. Keep the bare board off metal and away from liquids.
- A self-built dongle has none of the dongle's hardware protection; you build and use it at your own risk.