Risk of damaging the microcontroller. Badly designed circuit.

[rtek1000]

Hi,

As we can see in the electronic diagram, the LED of the relay can carry out a high voltage return if it fails in the reverse voltage, probably when using a power supply greater than the value that the LED supports in the reverse polarization (generally it is only 5V ).

See details in this issue: mister-grumbler/w1209-firmware#22

Please disclose this design error to avoid unnecessary damage.

[TG9541]

It's almost incredible that such an obvious design error has been copied hundreds of times and that maybe hundreds of thousands of W1209 boards have been sold!

I would suggest to simply remove LED "Red" or R7 and use one of the DPs of the 7S-LED display as a status indicator.