In-Circuit Programming (ICP) Adapter for Luminea TH Sensor

I purchased a bunch of Luminea TH-Sensors which a great but require a cloud solution for normal operation. They are built similar to a Tuya BTH-01 TH-sensor, for which a custom firmware for Tuya devices on the PHY622x2 chipset is available on GitHub. It is based on BTHome, works without the necessity for any cloud service and can be flashed onto the sensor through a USB-UART converter connected to several SMD test points on the PCB. 

My first setup using flexible arms with crocodile clips worked but was no fun to work with:

Positioning the pins so they make a reliable contact takes some time with this kind of setup, since the flexible arms tend to flex back a tiny bit, pulling back the pin. Spring loaded pins are much better suited for this task. 

For the pins I chose breadboard jumper cables, wrapped with adhesive tape at the isolated tip so they fit tightly in springs I harvested from some dried-up ball-pens (20mm length, 4mm diameter). 

For the RX and TX test pads, the pins had to be bent slightly to properly land on the pads. Accuracy obviously has its limits, but turned out to be good enough for the 2mm diameter test pads: Programming all of the 16 sensors worked flawlessly at the first try, just by slightly pressing the sensor board against the force of the spring-loaded pins while running the firmware flasher.

Disclaimer

Take this model as a proof of concept. You shall be aware that prying a product open to exchange the firmware at the very least voids all warranty. Worst case you short circuit and break your sensor, your programming tool (possibly other equipment) or both. Never attempt any of this on a sensor under power, never ever on a product that is connected to mains.