Obtaining the water temperature from a heatpump using a microcontroller

Question

There is a heatpump, which uses the following controller. How should one interface the heatpump, so the current water temperature (which is normally displayed only on a 4 seven segmen display, built in the controller) could be obtained and passed to a remote service.

I had two options in mind:

1. Use a Raspberry pi zero and a camera to perform some ocr on the built in display.
2. Use an ESP8266 or an Uno to interface either one of the 3 analog probes (which probably holds the temperature) or add an aditional ntc probe from the microcontroller.

How should one go about doing this? Thanks.

Answer 1

By the spec sheet it looks like the controller has some sort of remote control port on it, though the documentation is vague in that part. You may be able to figure that out, maybe by a phone call to the manufacturer, and use that.

Failing that, figuring out which probe is the one you want, and how it works, and tap into that using a suitable high impedance to not mess things up.

If you can not figure out that probe then add another.

The camera idea is cute though.

Answer 2

The easiest thing is probably opening the device and soldering a few wires onto the pins of the seven-segment display. You can then investigate which pin carries what information.

Note that it really could be as simple as having a pin for each segment, but in reality, it's probably a with a one pin that goes for example to all "top" segments of all digits, and a second pin that sets the active digit. By activating the digits fast enough, you can make it look like they're on at once. An easy way to find out whether that is the case is to take a camera with adjustable shutter speed, and set that as fast as possible.