Can a signal wire be run in parallel? (DHT22)

Hi,

Is it possible to run the signal wire from a DHT22 sensor to a digital pin on an Uno while also jumping the same signal wire in parallel to a NodeMCU (ESP8266 board for web readings). Everything will be powered from the Uno with a common ground.

Just want to know if you can take advantage of the same sensor will two boards.

Thanks

As long as both the Arduino pin and the ESP pin are configured as inputs, yes, that should be OK. Note that the ESP is 3.3V only so you should only do it with a 3.3V supply to all three boards. I don’t remember if the ESP can tolerate 5V inputs at it’s pins, but it’s better to just stick to 3.3V.

sdturner:
As long as both the Arduino pin and the ESP pin are configured as inputs, yes, that should be OK. Note that the ESP is 3.3V only so you should only do it with a 3.3V supply to all three boards. I don't remember if the ESP can tolerate 5V inputs at it's pins, but it's better to just stick to 3.3V.

Thanks for the reply. Yeah, ESP is 3.3V. NodeMCU board has a 3.3V regulator from VIN, but I'll be careful where i'm providing voltage.

Another thing to consider is the signal itself. The DHT22 is only driven LOW, and has to be pulled HIGH. So there's a pull up resistor.

It should work (never tried myself), if:

  • you make sure the Arduino and the NodeMCU do not attempt to read out the sensor at the same time. The sensor can be read every 0.5 seconds or so, so make sure there's sufficient time between readings as well. This may require some form of communication between the boards.
  • the pins are set to INPUT when idle - I don't know what the DHT22 library does with the pin when not reading it, you may have to do this manually. They should not be set to OUTPUT or you'd mess up the reading from the other device.
  • you have to use the internal pull-up (on the idle pin), and/or connect a pull-up resistor, unless that's built on to your sensor already (some come with a small breakout board which has this resistor present).

And of course use the NodeMCU 3.3V to power the sensor (and limit the voltage on the line to 3.3V), and connect the GND of both boards to have a common ground.

That should be it.