Wall control unit in parallel

[alryaz]

Hello, folks!

I was wondering whether or not it is possible to connect two devices to the S21 connector.

There's a wall-mounted control panel that becomes a paperweight once I unplug the S21 for it. Unfortunately I am unable to discover the location of the intermittent board it is controlled by, therefore I can't connect it to anything else directly.

Are there any measures to combine two devices into one? And what drawbacks am I expected to run into?

[njh]

Would quite like to have a wired-in control panel and temperature sensor too (instead of IR remote control).

I think it is very unlikely that you can just connect multiple devices together to the S21 connector on an air conditioner unit. I suspect devices will get confused by seeing responses to commands that they didn't send.

But it may be possible to build an S21 'hub' device, with multiple UARTs, routing the commands from one device to another.

@revk has implemented the S21 protocol, so may know better than me.

[revk]

Wall controllers are not usually S21 are they? But I guess if there is some intermediate board for it that would make sense.

Yes, one S21 port won't share.

But the way it works I suspect making an S21 hub thing is probably possible. And ESP32 has three hardware UARTs so doable, I am sure.

I have not worked out how to make a remote temperature sensor "feed in" to the aircon via S21, would love to know. But I have made a remote temperature sensor work with my Faikin module - it tells the Daikin high/low targets to maintain the temperature at the remote sensor. Works quite well. https://www.amazon.co.uk/dp/B0C2ZYXNYQ works with a BlueCoinT sensor.

[njh]

Just had a look at the Datasheet for my Daikin FTXM-R indoor unit: https://www.daikin.co.uk/content/dam/dauk/document-library/data-sheet/ac/R32/Split_SkyAir/FTXM-R_RXM-R_Datasheet_1011.pdf

It has a list of accessories that require the EKRS21 adaptor for the S21 port:

• BRC073 - Wired remote control
• KLIC-DD - KNX interface for Split type systems
• KRP413A1S - Adaptor PCB for remote on/off control - constant/pulse contact
• KRP928A2S - Adaptor PCB for interface to Daikin centralised control systems
• RTD-RA - Adaptor PCB for Modbus connection and/or extended system functions

It doesn't seem unreasonable to want to use more than one of these accessories at the same time but it does say: "Wired controller, KLIC-DI and RTD-RA options cannot be combined".

There are BRC073 units on eBay for not too much money. But having looked at the some of the PDF documents, there is nothing to indicate that it contains a temperature sensor. Which I find surprising - as I would have expected that an indoor sensor away from the aircon unit would be desirable. I can't find any other kind of temperature sensor accessories.

[revk]

Daikin don't seem to handle a remote sensor well anyway. My wired remote claimed to be able to be a temp sensor (and have a sensor in them) but never really worked as expected.

• [ ] That's why I ended up driving the aircon using its target temperature as higher or lower in order to hit the temperature I wanted from a remote sensor.

In an ideal world I'd be able to tell the Daikin the temperature it is via S21 and let it do what is necessary to hit that.