Hi. I have a project to monitor temperature and humidity at multiple place in a greenhouse. I want to use multiple DHT22 on a cable of at least 60 m (200 ft). I have cat5 cable in hand. What should i do? Use RS-485? I dont think i understand all about RS-485. Does i need an arduino with MAX485 for each sensor on the Line or i can only plug sensor on the max485 module? Tanks and sorry for my bad english... It's not my first language.
Well, since the sensor does not support RS-485, you will have to either use the protocol the sensor uses (sort of a 1-wire protocol), or use some extra circuitry to read the ship and send it via RS-485 (or some other multi-drop protocol).
The DHT22 needs a dedicated data line for each sensor.
You cant have multiple sensors on the same data line.
The maximum recommended line length is 30M.
I've got solution for my farm. My farm over 126m, and I've do anything to make my sensor can reach it... But nothing works...
At last I've found this : Maximum cable lengths for Dht22 and TMP36 Sensors - Sensors - Arduino Forum
I've tried 150m of UTP cat 5e, and It's stabilize ....
You could connect the DHT to an arduino pro mini and have a nrf24l01+ transmit the data wirelessly back to a central point.
This is how I get temp and humidity readings sent to my house from my greenhouse. Saves on the cable and it's easy to replace or reposition a sensor if you have a need to.
Skywatch.