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Topic: Replacement for DHT22 (Read 199 times) previous topic - next topic

sego

Hello,

i have a weather station based on Arduino Pro Mini, Waveshare 2.9 inch eink display, BME280 for inside temp, humidity and presure, SD-card for saving the data every 30 minutes, ds3231 for date and time stuff and the DHT22 for outside temp and humidity.
The problem is that my DHT22 seems to be more and more off. I use it since 2017 and at the beginning it was quite good, but now, especially in the lower area, it seems totally off and it seems to get worse.
Another DHT22 i have and the official data from the internet both are saying round about 40% humindity and the DHT22 from the weather station is saying 16.5%.
I could (and perhaps will) just replace it with a new, working one.
However, reading through the internet, i get the impression as if this type of sensor simply isn´t a good quality item.
The only problem is: I have only 2% flash memory left (SD-card and the display are using a lot !). And I soldered a self-made 3-pin-connector (VCC+DATAPIN5+GND) which i don´t really want to replace, because it would be a lot of work for tiny hands ...

So my question is:
Is there a high quality sensor that uses the same kind of 1 pin interface like the DHT22 ? This would be the easiest solution because it would almost only need software modification.

Another idea is to use a second BME280 for outside, because it could use the same library and therefore i woulnd´t run into flash memory problems. However, it needs 4 pins. Do you know if it´s possible to power it from an external source(battery) that is not connected to the Arduino and only use the 2 I2C lines from the arduino ? I sadly can´t test this at the moment.
I tried it back in 2017 with the DHT22 powering it from an external battery and only going with the 1 digital data pin from the arduino to the sensor and it didn´t work.
And another thing is: I´m using a very small board version without SDO pin. Like this one: https://www.ebay.de/itm/Breakout-Temperature-Humidity-Barometric-Pressure-BME280-Digital-Sensor-Module-/401000227934
How can i change the i2c address ? I suppose somehow with the soldering pads. But why are there 3 soldering connection points ?


Thanks.

rmvansomeren

Hi,

I don't know if you managed already to figure it out. If your second option with using 4 wires and a different I2C address is an option you can also have a look at the HTU21 datasheet:
https://datasheetspdf.com/pdf/1087268/TE/HTU21D/1.
Its more reliable than the DHT22 and quite easy to use.


sego

#2
May 24, 2020, 12:25 am Last Edit: May 24, 2020, 12:26 am by sego
i just replaced the DHT22 with a new one. Every other solution is too much work for me. I would have to tear apart the whole weather station and maybe even run into flash memory problems.
The HTU21 would not be an option, because of a new library which i cannot use because i only have 2% of flash memory left. It´s not about if the lib is easy to use, it´s about saving flash memory at all cost.
I already had to use the tiny-bme280 lib because the standard ones were way too big for this project. I hoped there would be a better sensor with the same 1-pin-connection. But it seems as if this doesn´t exist. So ... I keep it as it is.

But maybe for all wanting to do such a project: If it´s serious, don´t use the DHT22. It´s not a reliable sensor.

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