SM2335EGH-rs

A GPIO-based driver for the SM2335EGH LED controller found in the SwitchBot Color Bulb, written in pure no-std Rust.

The SM2335EGH (aka just SM2335) is a 5-channel, 10-bit LED controller made by Shenzen Sunmoon Microelectronics. Some details about the chip can be found on their website, chinaasic.com. Alternatively, you can find the document with the specs here in doc/.

In short, the five channels (called OUT1 through OUT5) are essentially split into two groups. The first three channels (OUT1-OUT3) are low voltage at 40V and allow a maximimum current of 160mA. In practice, these three channels are used for RGB / coloured light. The last two channels (OUT4-OUT5) are much higher voltage at 500V, but the maximum current is halved at 80mA. These two channels are used for warm & cool white.

In my SwitchBot bulbs, this is the concrete channel mapping used:

This chip seems fairly uncommon at this point (2023-09). At least I'm not aware of any other products than the SwitchBot bulbs that use it. The specific model number of my bulbs with this chip is W1401400.

Implementation

I just based the driver on the ones in Tasmota and ESPHome. I've asked the manufacturer for more information about the protocol, just to have a first hand source, but I'm not particularly worried about bugs. The protocol as found in the Tasmota and ESPHome implementations is really simple, and I haven't had any issues in practice.

However, if you happen to have access to the protocol specification, please contact me! Similarly, if you've spotted an issue in the current implementation -- don't hesitate to open an issue (or even better, a PR).

License

The MIT License (MIT). See LICENSE.