This firmware can be flashed on:
- LilyGO T-Display-S3-AMOLED
- WaveShare ESP32-S3 1.91inch AMOLED
Both models are dev boards based on ESP32 SoC and featuring a 240x536 AMOLED display panel. As most Espressif SoCs, they support WiFi (2.4 MHz only) and Bluetooth + Bluetooth LE.
This project is a from-scratch reimplementation of my other project that uses ESP-IDF instead of Arduino. I got unhappy about the way BLE support is implemented in Arduino, and decided to try an alternative (more professional?) SDK.
I was lucky to find a fairly new (as of this writing) driver for the AMOLED display chip that seems to work for me with ESP-IDF SDK.
When you turn on the device, it runs BLE scan trying to find either an HRM sensor (one of those chest strap fitness gadgets), or a Viatom ECG recorder (one-lead ECG recorder marketed as "Heal Force" or "Prince" or some other strange brand, that usually has "PC-80A" or "PC-80B" written on it).
Chest strap sensors do not provide ECG readings, but they do provide the sequence of RR interval durations. In this case, this gadget generates a simulated ECG that represens RR intervals received from the sensor.
PC-80B recorder provides real ECG reading, sampled at 150 Hz, as a stream of BLE messages. In this case, we are able to display real ECG trace, in near real time. Recorder has to be set to "wireless" mode via its "Settings" menu.
- Install ESP-IDF (refer to the documentaiton, link above).
- Clone this repository
- Follow IDF instructions for building a project (
idf.py set-target esp32s3,idf.py build,idf.py -p <tty-where-the-module-is-connected> flash). - Have a running PC-80B or HRM in the vicinity. You should see ECG trace running on the display in a few seconds.
In the "Releases" secton on github, you can find zip file that contains
pre-built binaries that can be flashed onto the module. Flashing requires
esptool program. On many Linux distros, there is a package available in
the standard repository.
Start the gadget by pressing "reset" button.
After some time, if it does not find a source, it loses hope and goes to deep sleep. You can make it go to deep sleep by pressing "the other" button (the one that is not "reset").
There is an openscad design for a 3d printed case for the Lilygo version of the board (T-Display-AMOLED v2.0) with 320 mAh lithium polymer battery. Adjust dimentions if you use a different version of the board or a different battery.
- Waveshare module has reversed button positions compared to Lilygo module.
- Lilygo has GPIO4 connected to the battery voltage divider, Waveshare has GPIO1. The program will try to figure out where is it running (better than having two separate binaries?).
- Waveshare and Lilygo have slightly different geometry; provided box design is for Lilygo. It has to be adjusted to fit Waveshare.