Hi everyone,
From time to time, I tend to be a little ambitious, so after installing 10+ shelly's across my home and hooking them up successfully to OpenHAB, I want to make my elevator "smart". That's to say, it would be cool to know at what level the carriage is positioned to start with, maybe even control it later on.
I'm no pro electronics engineer, but I can hold my own with a soldering iron and I know Ohm's law, so I'm trying to implant a Shelly Uni onto the return wires of the buttons that come back from the elevator carriage. I'm attaching a picture of those buttons to this post. Note that the buttons have LED lights that indicate at what level the elevator carriage is positioned (the light of the respective button lights up when the carriage hits that floor).
I'm attaching the relevant schematics too: when a button is pressed, the 12V is pulled down and a relay is triggered, that controls the motherboard of the elevator in its turn.
I'm taking the GND and the 12V of the source to power the Uni and it boots without a problem. The relevant buttons for level 0, 1 and 2 are C0, C1 and C2 on the schema. When measuring the line to GND with a multimeter, they all have a nice 12V when the light around the button is off. However, when the light is on, they are around 6.3V.
So I thought: if I hook up the button wire to the ADC_IN of the Shelly Uni, I can use it to distinguish between "carriage not there" = 12V and "carriage at this level" = 6V. I'm hooking up the Uni like this:
wire 1 VCC = stable 12V from the elevator power source
wire 2 ACD_IN = the wire that comes from the elevator button switch (open side of the switch, see "C0" on the schematics)
wire 6 GND_SENSOR = 0V from the elevator power source
This boots up the shelly nicely and the voltage input is around 12V when the light around the button is out,
HOWEVER: when the light around the button lights up (carriage is at that level and the voltage drops to +/- 6V), the ADC voltage input on the shelly start to float anywhere from 0V to 12V and back. The load on the wire is around 2mA when the light is on.
So here's my question: do any of you have any idea why the input reading on the ADC_IN starts to fluctuate when the light turns on? Do I need to add a pull-down or pull-up resistor somewhere? Should I also hook up wire 2 (N) to GND on the Uni? I can test or measure anything, just let me know.
Looking forward to your help.
b.