Hackaday · Creativity & design

ESP32 Bluetooth Printer Driver Developed Through Reverse Engineering

A maker successfully created a Bluetooth printer driver for an ESP32 microcontroller by reverse-engineering the printer's communication protocol, bypassing the need for a proprietary smartphone app.

The project aimed to control a portable Bluetooth thermal printer with an ESP32-C3 microcontroller to print sensor data reports. The manufacturer only provided a proprietary smartphone application, with no public documentation on its communication protocol.

Instead of the typical method of logging Bluetooth communications via Android debugging and analyzing with Wireshark, the maker used a different approach. He utilized an application to query the device, list its Bluetooth Low Energy services and characteristics, and then experimented by writing data to writable services.

Using Python with the Bleak library, he rapidly iterated and tested, eventually discovering the correct sequence of commands to activate the printer's motor and advance the paper. This confirmed he was on the right track.

Once the data payloads and endpoints were identified in Python, the process of sending the same information using C++ on the ESP32 was relatively straightforward.

The project also incorporated the Adafruit GFX library to enable the creation of icons and improve the printer's output formatting.

While the code has not yet been publicly released, this effort highlights a common challenge with proprietary devices and demonstrates a successful method for developing open-source drivers for such hardware.

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