TX3 to Sika VVX20 Flow Meter

You didn’t mention that before!
Yes, I think you may well find a pulse there, but the comment about pin use might mean it’s custom software and it’s not included.

If that’s the case, if you’re careful then monitoring the voltage output will probably still work, but you must make sure that everything you use to do that is isolated from everything else except the heat exchanger - i.e. you use an isolated mains supply to your Arduino and opto-coupler or radio to get the data out.

Thank you. I have setup a Arduino to read a handful of DS18B20 thermometers and issue the data via MQTT. I aim to get this setup over the next few weeks.

Happy to share the code if anyone wants it.

I am then going to get a oscilloscope and test the output of the flowmeter. I suspect that I will find an unused pulse, which I can connect via an optical coupler to a second Arduino.

@gck303 - George, did you connect your VVX20 Mitsi to your EmonTx3 in the end? I have an identical (Ecodan) pair of pumps, and am trying to connect to an EmonTx via the digital output . Any insights follwing on from your Jan post would be really helpful.

I guess plan B would be to assemble the dedicated board, which is where your post started off…


The same (or very similar) flow meter is also included as standard with Samsung heat pumps, although the part number looks like it’s Samsung specific.

@gck303 did you have any luck testing the pulse output?

I’m installing a Samsung heatpump soon, so I’ll try and test.

To intercept the signal from the flow sensor while the sensor is plugged into the ASHP controller we need to make a mini PCB adaptor. This is the plug that my Samsung branded VVX sensor came with, can anyone identify what plug this is and what connector will be required to plug into it?

@gck303 can you confirm if your Mitsubishi branded VVX has the same connector?

It’s a silly question - is there nothing anywhere on the moulding? Knowing the pin spacing and physical dimensions might allow you to narrow the choice down. It almost looks automotive.

The headers on the PCB look similar - is there any marking on those?

There are no markings on the connector.

The dimensions are 10mm x 5mm and the pitch is 3mm

Sorry, I don’t think I can put a name to that. I have a feeling I’ve seen one, but that’s about all.

Have you tried uploading an image of it to Google Lens?

The closest I could find were these ‘JST’ type connectors from TE Connectivity:


But that’s 3.98 mm (call it 4) pitch, a 4-pin is 15 mm long, not 10.

It might still be worth sending the pictures to Mouser or TE with a “Can you identify this?” plea.

I think I’ve found the connector:

But the RS product listing doesn’t give any info as to compatible resereceptacles. I think it could be Smw250, but these look hard to get hold of:

It looks like the same part is used for Samsung A/C sensors:

There’s an obvious reason why you didn’t find it earlier: from the data sheet…

Connection Gender Male
Connector Type A Circular Plug


It’s probably worth an email to RS asking for details of the mating connector.