So last month we began exploring the SHT45, starting with the probes themselves. By pairing them with ESPHome and Wi-Fi, we created the THS45 – essentially bare probes. We're delighted they appear to be functioning rather well.
Now let's do something rather fun. We've modified quite a few THS-M6 units. These feature CR2450 batteries, a decent-sized screen, and sensors close to the SHT40 (though suppliers may vary slightly). . Now we're swapping the M6's temperature and humidity sensor for the SHT45 – a rather impressive piece of kit – giving us a highly accurate humidity and temperature sensor.
This could be a rather nifty little gadget: same size, but with a significantly more precise sensor. Coupled with the powerful open-source firmware shared by ATC and PVVX, you can freely adjust update frequencies, change names, and do all sorts of quirky, cool things.
I reckon it's a rather splendid contraption, given its commendable precision.
We've dubbed it the THS-M45, our initial modification target for the BTHome firmware release.
Enjoy tinkering with it, and a very Happy Chinese New Year!
Let's briefly summarise what's inside this contraption:
- It runs on a CR2450 battery, theoretically lasting over eighteen months (though we haven't been able to test it that long yet), which is twice the lifespan of a CR2320 battery.
- Using the BTHome broadcast protocol, any HA with BLE capability will automatically discover the device, adding it in under a second.
- It employs open-source firmware from PVVX and ATC, offering advanced configuration via a web management interface for setting refresh rates, screen behaviour, and various bespoke functions.
- The sensor has been upgraded to the SHT45, arguably one of the most capable temperature and humidity sensors currently available. Its most significant advantage lies in substantially improved humidity accuracy.
Accuracy Improvements (Typical)
Relative Humidity (RH):
• SHT40: ~±1.8 % RH typical
• SHT45: ~±1.0 % RH typical (better precision) 
Temperature (T):
• SHT40: ~±0.2 °C typical
• SHT45: ~±0.1 °C typical (twice as precise)
