I have a De Ditrich brand central heating + DHW furnace with a controller installed in a detached house. I would like to record the fact that it is switched on and off. As I plan to do this without too much reworking of the working solution, I came up with the idea of connecting to the LEDs on the panel that light up when the furnace is running.
I dismantled the panel, which looks like this:
The LEDs I am interested in are located at the bottom (3 pieces). From analysing the paths on the board, I worked out that these LEDs share a common ground (the path above them) - I soldered a cable there.
I then soldered the 3 cables to the individual LEDs (from the bottom) at the A marking (I think it was like Anode). Testing the correct connection with a meter, the LEDs even lit up slightly, so the cables are conducting correctly.
And now the strangest thing, which surpasses my knowledge of electronics:
When I measured the voltage on the individual LEDs, the multimeter showed "-1.32V" when the LEDs were not lit and from "-0.6V - -1.0V" when they were lit. I was expecting about a 2V drop on each LED, not negative values. Furthermore, when lit, these voltages varied and were probably also dependent on the digital display (on top of the board).
My request/question:
- how to explain the above strange readings?
- how else to detect the on/off of the cooker (without extensive interference with the original controller)? I rather skip registering temperature changes on the pipes because that's not a very accurate way.
I dismantled the panel, which looks like this:
The LEDs I am interested in are located at the bottom (3 pieces). From analysing the paths on the board, I worked out that these LEDs share a common ground (the path above them) - I soldered a cable there.
I then soldered the 3 cables to the individual LEDs (from the bottom) at the A marking (I think it was like Anode). Testing the correct connection with a meter, the LEDs even lit up slightly, so the cables are conducting correctly.
And now the strangest thing, which surpasses my knowledge of electronics:
When I measured the voltage on the individual LEDs, the multimeter showed "-1.32V" when the LEDs were not lit and from "-0.6V - -1.0V" when they were lit. I was expecting about a 2V drop on each LED, not negative values. Furthermore, when lit, these voltages varied and were probably also dependent on the digital display (on top of the board).
My request/question:
- how to explain the above strange readings?
- how else to detect the on/off of the cooker (without extensive interference with the original controller)? I rather skip registering temperature changes on the pipes because that's not a very accurate way.
Of course I do not guarantee that it will work in every case.
