Has anyone looked/tried Xiaomi Mijia Temperature Sensor (Bluetooth) ?
Yeah i’d heard the same which was why I was going to change over from DHT22s to BMEs.
I did an experiment with an alcohol thermometer, two DHT22s, two BME280s, two Xiaomi CGG1s and a Xiaomi LYWSD02. I put them in the same place and watched them for a week. I made sure the sensors were well apart from the ESP board, as that heats up.
DHT22s - fast updates, accurate enough.
BME280s - fast updates, but consistently high readings which affected the humidity reading
CGG1s - slow as a wet week, i.e. not enough updates even for room temperatures (BLE broadcast)
LYWSD02 - frequent enough updates but high temperatures again (BLE broadcast)
The DHT22s seemed to give the most accurate temperature (assuming my alcohol thermometer was accurate) with the fastest updates. They’ve been running reliably for over a year, so I ended up keeping them.
I guess it’s true, if you have more than one thermometer all you have is confusion 
I have some BMEs, CGG1s and a LYWSD02 for sale if anyone wants them (Australia).
hahahaha. Very true.
The Si7021 I have is consistently lower temp than the BME280 but it’s also in a different part of the house… about 2° lower consistently.
I might grab a DHT22 and put it in the same location as the BME280…
That’s actually disappointing because they’re perfect i.e. stand alone, battery powered and can be mounted anywhere without needing to wire in power.
By “not enough updates” for the CGG1 - how often can it do?
And for LYWSD02, can you tweak the offset so it matches up?
Thanks.
For sure with a template you can apply an offset or pretty much any formula you desire.
Green line is the CGG1, Red is LYWSD02, both are currently next to each other. The blue line is a DHT22 in an adjacent room.
I know nothing about this sort of thing, which will probably show in my question, but could it be possible to build something that uses the DHT22 and is wireless and battery powered (for example, with a couple of AA) so that self contained units could be built and placed anywhere in the house?
Not if by wireless you mean WiFi. Too power hungry. You’d be lucky to get more than a few days on a couple of AA batteries.
For BLE, Zigbee, Zwave or ISM RF you’re better off buying rather than building.
However if you power it from a 5V plug pack an ESP WiFi module loaded with ESPhome and configured with yaml is very doable. It’s what I use.
Good article to get more power out of batteries for a esp8266 but it does indeed mean lesser readings https://openhomeautomation.net/esp8266-battery
That’s a pretty bad article. The author is only accounting for sleep current. Waking for 30 seconds (optimistic) every ten minutes would use 600mAh a day (@0.5A TX current).
Ha good catch it would indeed add up more power consumption
Thanks for the replies
Personally I don’t mind how for the wireless
I am not so keen on powering by a plug, plus where I would like to put a couple of sensors they are not close to sockets
I already have a couple of aeotec multisensors l, but they are around £60 each and I am really only interested in humidity and temp
I’ve come across this…
Seems to be grabbing data better than previously - are you able to test it with CGG1 and LYWSD02 and see if it worked for you before I buy them?
Thanks.
No. I run home assistant on a pc without Bluetooth. The sensors are communicating with an ESPhome flashed ESP32 board that acts as a gateway.
No love for the xiaomi zigbee stuff?
Horrible wifi interfering things!
But seriously, they are a great option id you are not using all three non overlapping 2.4GHz wifi channels.
with regards to the
CGG1s and a LYWSD02
does anyone have any information on what the actual sensors they use in them i.e. is it a BME280 with smoothing etc and thats the reason for the slow updates ?
Not sure what the sensor is but the low update rate would be to maximize battery life.
Not a cheap solution but I’m using Philips Hue sensors. They have built in temperature sensors that are not reported in the Hue app but are in Home Assistant. Requires hub.
Ohhh, do tell… I have Philips Hue with hub. Thanks.