Humidity Sensor Shootout

If you want to measure humidity (and temperature, and maybe even barometric pressure) in a device that you’re building, have a look at this comprehensive test of seven different options. We’re going to summarize the results here, but you’ll really want to read up on the testing methodology — it’s great science hacking. Did you know about using saturated salt solutions to produce constant humidity levels for calibration? We didn’t.

The so-called DHT22 module doesn’t fare all that well, with one of six that [Robert] tested being basically horrible, and three of them breaking within two years of use. The one that works well, however, is pretty good. Feeling lucky?

The Bosch BME280 looks great. It costs a bit more as a bare part, and a few times more than mounted on a friendly module, but it seems to be very reliable. And you get a barometer thrown in for the extra work. Indeed, it performed so well that Hackaday contributor [Nava Whiteford] put the part under a scanning electron microscope to figure out what’s going on.

The other sensors were fine, with the HTU21D and SHT71 being standouts for their ultra-fast response. For the full details, go click on that link at the top. Having just installed a sextet of DHT22s in our house last year, we’re left with that sinking feeling that we may have gotten what we paid for, which wasn’t much. At least they’re all still running.

Thanks to [Dodutils] and [mac012345] via comments in another thread.

Filed under: hardware, home hacks

Adjusting clock with alarm, hygrometer & thermometer on 1.8″ ST7735 display


Nicu Florica blogged about his adjusting clock with alarm, hygrometer and thermometer on 1.8″ ST7735 display:

I use feature from article Another adjusting clock with alarm & thermometer using DS3231 on 1.8″ ST7735 display and change reading internal temperature of DS3231 with DHT22 senzor (AM2302), but you can use a cheaper and not very precise DHT11 senzor.
By using educ8stv_rtctft160_alarm_dht.ino or much better educ8stv_rtctft160_alarm_eeprom_dht.ino sketch, on display you can see: name of day, date, hour clock, hour alarm, temperature and humidity

Project details at Arduinotehniq blog.

Check out the video after the break.

Adding a DHT22 temperature and humidity sensor to the Sonoff

DHT22 temperature

Mikey writes:

Just a few days ago I replaced the firmware on my Sonoff, and immediately after, I wanted more…
After looking on their website, I found a version which also had a DHT11 sensor attached, and I then wanted to do something similar, just with a DHT22 for higher resolution (0.1C on a DHT22, compared to 1C on a DHT11). After digging a bit more in the schematic for the Sonoff, I found that the last pin on the 1×5 pinheader, was connected to GPIO14, so it should not be that difficult to get up and running.

More details at