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A strange question, but you are the only blog on the internet that has disassembled a HR92. Do you have any pictures with the components/silk in place? I want to fit a regulator so it may be powered from USB instead of 2x AA battery.
I guesss you have the HR92, just open it and see for yourselves. Opening it is quite easy and revertable.
Thanks Marco. I don’t have easy access to the HR92 – it’s for my parents in another country. More of a thought experiment for now! The silk or component labels were because you have a list of the components, but no locations! I can guess though.
It’s challenging since the power rail exposed to the USB port is the microcontroller (1.8v?), whereas power in should really go to the BATTERY+ (~2.8v), so it feeds the motor. So some more wires are needed.
The microUSB is used for “Cable ACS90” and “window contact HCA30”, which appears to use the green wire (D+?) to black (GND?) as a normally closed window opening detector.
https://static.rorix.nl/document/product/overig/c2004120ba4791d01c89b6e2a458216c.pdf lists another use – the white wire (D-?) to GND supports an external NTC thermistor, either separately or in combination. Finally a HCW23 can be connected with all three wires as an external thermostat – but I think this requires no special logic, since the window open detector already closes the radiator valve, and the temperature sensor needs simply be an NTC. The NTC could be detected, but the window close sensor (or cable detect) needs configuring or another pin used as plug detect.
What’s puzzling then is that all 4 (D-, D+, ID, and V+) pins from the microUSB go to the microcontroller! Is there a hidden programming interface? V+ is actually decoupled to GND – so may
In fact there is /another/ cable: “ACC90” which allows connecting two HR90 devices together! And allows copying the time programming from one master device to another. Unclear if the cable is asymmetric or there’s software. That presumably takes another pin…
Finally there is an “APS90” device which I can find absolutely nothing about, which claims to be “HR92 power supply PCB” which sounds like problem solved, if there was any information about it 🙁
D+ and D- go to TXD1 and RXD1 on the ATMega, presumably they do the master/slave comms, window detect, and plug detect. ID looks like it’s complex enough to be the NTC reading. V+ from microUSB appears to go to microcontroller PA7, and is connected via a 3-pin device to the GND and “Inner 2 red” power plane. If we assume that it’s protection diodes, and that there’s also a small pulldown to GND, this fits with an NTC quite nicely.
The USB ID pin is puzzling though!! It’s connected to a lot of pins, again has 3pin device to power and gnd – “CC CSn”, pin 7 of the mystery 20 pin IC, PA2 of the ATMega, linked to one of the display pins, and PA4 of the ATMega too. I don’t know what it does!
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