Help identifying protocol for Midea AC daughter PCB communication

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1

I have a basic Midea AC unit that lacks Wi-Fi connectivity, and I’m interested in making it smart. It consists of a main PCB, which I prefer not to tamper with, and a smaller daughter PCB responsible for receiving remote control inputs and communicating with the main PCB via four wires. The daughter PCB features a SinoWealth chip (SH79F1612A) (SinoWealth 中颖电子).

I managed to intercept and analyze the signals on the four wires using a logic analyzer, but I’m struggling to identify the protocol being utilized.

Despite thorough research, I remain at an impasse.

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It repeats every 270ms.

Here is the Logic session: Session 1.sal - Google Drive

I used Saleae Logic 2 on win11. I measured before messing with anything, the logic is 5v.

2

Which channel in your capture goes with which pins on the SH79F1612A?

[Edit] reviewing the data sheet – looks like the most common peripheral is UART:

Pins 17, 18 have RXD, TXD (EUART) and 7, 8 have RXD1, TXD1 (EUART1).
Were any of these the ones captured?
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Doing some quick measurements on Channel 0, you can observe:

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The period is 4.173 ms
Assuming a standard 8N1 UART protocol, this means one bit period is 4.173 ms / 10, or 417.3 us/bit.

That works out to 1 / 417.3 us == ~2396 bits/s, which is close enough to assume a standard rate of 2400 bits/s.

To test that theory, you can decode with these settings (add an analyzer to channel 0):

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… and use the same settings on channel 2 – which might just have more idle time between bytes. From this point, it’s a matter of studying the decoded data and trying to correlate that to the system (e.g., when something is on or off, displayed values, etc.)

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3

Wow, I can’t thank you enough! I must have experimented with every async serial parameter, but none seemed to do the trick. Perhaps I should have taken a more analytical approach like you did.
That push was all i needed, now I’ll try to decode the information, there are some github repos that are promising.
Thank you again!

4

Hello. I’m also interested in this topic. I have a DEXP air conditioner manufactured by Midea. The display board doesn’t have a connector for a WiFi dongle. I dumped the data exchange between the display board and the motherboard and used chatgpt to decode the protocol. In summary, I can say the following: it’s a 2400 baud 8N1 UART. Currently, I have an external component for ESPhome that allows me to collect system status (temperature, mode, fan speed) from the data exchange between the display and the motherboard. GitHub - Ra3mbl/esphome-carrier-uart-ir
This is just a draft; for now, it only allows you to view the status in Home Assistant, but I wanted to add the ability to send commands to the air conditioner by modulating a signal to the IR receiver pin. The remote control protocol is detected as Carrier, so I named the library carrier-uart.

But the most interesting thing is this. I bought a Midea display board with a Wi-Fi connector. I connected it to my air conditioner’s motherboard, and it worked! This means it communicates with the control unit using the same protocol, and a Wi-Fi dongle can be connected directly to it.

Therefore, the easiest way to add Wi-Fi to this air conditioner is to simply replace the display and install a Wi-Fi dongle.