Hi there,
▸ tl;dr
It’s not possible to extract 433MHz RAW data from Sonoff RF without any major modifications to the hardware. I figured this could be helpful for anybody wondering and trying to achieve the same. So you’d have to waste less time now.
Sonoff RF, PCB version unknown
▸ Idea
Since quiet some time I had a specific idea for the three Sonoff RF (not RF Bridge) I own.
I wanted to use them as an universial receiver for 433MHz remote control signals and place them in different corners around the flat. Primarily I intended to use them with those long-lasting, cheap-ass 3, 4 or 8 button remotes as input devices.
Abstract approach:
433MHz generic remote button press → Sonoff RF → ESPHome remote_receiver → ESPHome internal OR Home Assistant internal logic → trigger action in Home Assistant
▸ Analysis
It was rather hard to find any information as how to proceed at all, which is rather unusual as the hacking-all-ESP-enabled-devices-community normally is quiet active. Posts about hacking the Sonoff RF Bridge are found lot more frequently. So I did some digging.
Facts
- The Sonoff RF is a Sonoff basic with an additional 433MHz module soldered to it. It was sold this way by Itead.
- Tasmota is able to freely program *one* remote control to (de-)activate the relay.
- ESPHome doesn’t list any specific pins for the 433MHz module. esphome-devices.com doesn’t list the device at all.
Being at the point I’m now, I consider [2] & [3] already as strong indicators it wouldn’t work (at all (“out of the box”)).
I did some further googling and had a look at the datasheet of the chip SYN470R used on the 433MHz module PCB soldered to the Sonoff RF main board.
- The 433MHz chip datasheet states in the very first two sentences:
The SYN470R is a single chip ASK/OOK (ON-OFF Keyed) RF receiver IC. This device is a true “antenna-in to data-out” monolithic device.
(Where ASK refers to the utilized modulation and stands for “Amplitude-shift keying”.)
For me, this directly translates into “the ESP onboard the Sonoff RF never sees any RAW data as the chip directly translates it to an ON-OFF-signal and passes it on to the ESP”. Sad.
- Furthermore this is backed by a forum post I found on electronics.stackexchange.com:
[…] the 433MHz card behaves in the same way [after flashing Tasmota] as it did with the original OEM Itead firmware.
This fits together with the statement in [2], remarking that
Pairing the iTead RF remote controller is the same as with the original iTead software.
So the progamming of the remote transmitter to react to happens independently of the ESP firmware. Sad.
- Finally, as Itead has some quiet transparent documentation available on their homepage, I was able to review the schematic of the Sonoff RF which reveils that between the 433MHz board and the ESP just one connection exists, called “E-FW”. Sad.
▸ Synopsis
It’s not possible to extract 433MHz RAW data from Sonoff RF without any major modifications to the hardware. As the post in [5] implies, there might be some chance in modifying the 433MHz board, but this is definitely out of my league.
Sad, that I’m not able to achieve what I’ve though of for quiet some long time already - due to hardware limitations. Still, happy that I finally figured it out with some proper evidence and can move on with some other little home automation projects.
Really hope this was an interesting read and helps somebody.
Cheers!