I didn’t think it was going to be easy, and indeed it is not. I built the same setup as for my Hitachi AC units, added the debug_discovery text sensor and buttons and gave it a go. But the ESP32 board doesn’t start.
When unplugged, I checked the voltage of the heater’s CN7 pins:
When plugged, 5 and 6 get shorted, and I measure ~2.4V between 1 and 5. I have tested the same setup and buck converter on a climate split and it was working.
I don’t have an oscilloscope so I’ll leave it at that for now, and try not to fry the motherboard of the heater.
Thank you for your efforts in reverse-engineering the Yutampo h-link protocol.
Were you able to figure out which device is supposed to be connected to the CN7 connector on the Yutampo? I have found several adapters listed as compatible with the Yutampo series, such as the ATW-HCD-01 or ATW-TAG-02, but all of them appear to use the 2-wire H-Link connection.
As far as I understand, the ATW-HCD-01 is an adapter that converts the 6 pins CN7 H-Link connection into a 2 wires one, on which you can plug the ATW-TAG-02.
On Hitachi ACs, pin 6 controls whether the AC accepts ST commands. When pin 6 is logical HIGH (the default value, that’s what you measured), the AC accepts and responds only to MT (read AC status) commands. When it is LOW (connected to GND), the AC handles both MT and ST requests. Pin 3 is also NC in Hitachi ACs CN7, so in general the connector pinout looks quite similar.
Therefore, even without pins 6 and 5 shorted, you might still observe some UART communication from the device. The main question though is what protocol is being used and whether it can be reverse-engineered without a reference device.
Thanks for the insight. Unfortunately, when I short 5 and 6, pin 1 doesn’t deliver 12V anymore and I am not able to power the esp32. If I understand correctly, the fact that pin 6 is HIGH means that I wont be able to control the water heater features, and would only be able to read them at best (if I can make some sense off the protocol). Disapointing, but an interesting hack nevertheless.
My next step will be to scratch current setup and restart with some lower level logic analysis. I don’t want to polute this thread with non-AC related stuff so I might reach out in DM for a couple of questions, and will update the community if I find or make anything useful.
that is correct. I asked my supplier on how to integrate or get an app on the Yutampo and got this chain ATW-HCD-01 → ATW-TAG-02 → AHP-SMB-01. I would love an integration to controll and / or read temperatures / modes from the tank.