One month ago I wrote about the Sonoff SC from ITEAD, after having used it for a month, do I think it is any good?
I have tried to have it a few places, to test how the readouts from it would be, here it is in the window at my dining room. Here I tested the light sensor to see how how much it took to make it go between its 3 different readings.
I had it in my bedroom while shaking the rug to see the air quality readings.
And I had it in the living room to see how much it took to make the sound level change.
The combined temperature and humidity sensor seems to be a bit off, and very slow to react. I had expected some deviation and slow reaction, since it is mounted inside the case and therefor not getting any airflow around it. The temperature reading is also about 2 Celsius higher than the other sensors I got.
I am not sure what the light sensor is calibrated after, so far the highest I have seen it read is “Normal”, where it isn’t taking much to make it go down to “Dusky”.
This I am not entirely sure how works… Sometimes it falls down to quiet when having some low music on, turning the music up makes it read it is noisy, turning it down again makes it go normal, and lower back to quiet again. But it can also read normal in a completely silent room, where it is easier to make it go down to the quiet reading with some low noise, instead of no noise…
During the month I have used the Sonoff SC, I only had air quality to read “Good” which is the best reading. Even in my bedroom after shaking everything, I could in the sun clearly see a lot of dust in the air, the reading was still “Good”, I then took my vacuum cleaner, removed the particle filter just before the motor, kept the bag in, and started it. It then blows a lot of fine particles into the air, after keeping an eye on the SC for the next half hour, the reading was still “Good”, so I guess the dust particles never get into the housing where the sensor is located.
After a month, I am not really sure what to use it for… The temperature sensor seems to be good enough to get a rough idea about how hot it is in the room, but the remaining sensors seems to be more or less useless.
The look of the case it is mounted in looks decent, but does not seem to be the right choice for having such sensors inside.
The SC is easily added into the EWeLink app, where there is the option to add scenes. Scenes can be set up to turn the Sonoff Switches on and off, based on a trigger from something else. And since the SC got a temperature sensor in, lets try and use that to trigger a switch, and by that making some room heat control.
First I make a new scene, and in that I use the temperature sensor in “Livingroom”, which is the Sonoff SC. If Temperature is below or equal to 20, turn “Livingroom heater” (a Sonoff Switch), on and start heating in the room.
I do the same to turn it off, so if temperature is equal or above 21, turn the heater off.
In theory, temperature should then be between 20 and 21 Celsius.
After some testing, I must say it isn’t really usable either. Turning the Sonoff Switch on and off works fine, the problem is how long it takes for the temperature reading to change enough to make it switch. So the room ended up getting a lot colder than it was set to be, and ended up with the heater turned on while being well above the set point where it should be switched off. The highest temperature was 24 Celsius, where I then manually turned it off, it then took quite some time before the temperature reading came up to the room temperature, and the switch turned off.
With this, there are two problems. One of them is the case which is insulating the sensors inside from the air outside, so the reading is delayed, and offset. Another problem is the use of a DHT11 sensor. This sensor only measures in whole degrees, so it needs to change a whole degree before it is noticed, this added on top of the delay from the case, makes it too slow to be used as a trigger.
To compare, I tried to make my own system which I have described some time ago too http://captain-slow.dk/2016/04/03/simple-temperature-control/
With this I run it all locally on my own server. The temperature sensor is the slightly more expensive DHT22 sensor, which reads down to 0.1 degree intervals, which makes it react a lot faster to temperature changes. At the same time, I set mine to do a reading every second, and then use a filter so it affect the previous reading by only 10% of it’s value, with this setup I can set the trigger to trigger at 20 Celsius. Which does not make sense in the EWeLink app, because it is possible to actually set it to turn on and off if temperature is equal to 20… But with my own, I can set it to turn on if temperature is below 20, and turn off if temperature is above or equal to 20. Readings then show temperature goes up and down from 19.4 to 20.5 Celcius, which is a lot more acceptable.
I am still not sure what to use the Sonoff SC for, none of the sensors report anything I can actually use, but maybe I can replace the DHT11 sensor with a DHT22, and do some modifications to the case, and then by that make it usable.