Hi, as a newbie I am looking for some advice as to which DHT22 senor type I should use with my UNO R3. There are different types. Ones that have 4 pins and 3 wires as in photops attached and one which are mounted on small boards as in photo. What is the difference of the ones on the small boards?
1st one and 2nd one are identical, just external case is different, and the 2nd one you can solder it essayer on a PCB not easy to use in a breadboard.
The 3rd one is the same as 1 one with pcb mount with pull-up resistor and a cap. Easy to use in a breadboard without additional pull up resistor required for DHT22 as it already provided on the PCB.
So, just depend where are you mount this sensor.
Thanks @arssant. I will probably be mounting in small enclosure so the pcb one would probably be more convenient. What is the function of the capacitor? I understand that a 4.7K pull up resistor would need to be added to the first 2 but what about the cap?
Snootyfox:
Thanks @arssant. I will probably be mounting in small enclosure so the pcb one would probably be more convenient. What is the function of the capacitor? I understand that a 4.7K pull up resistor would need to be added to the first 2 but what about the cap?
From adafruit:
"Power's voltage should be 3.3 -5.5VDC.
When power is supplied to sensor, don't send any instruction to the sensor within one second to pass unstable status.
One capacitor valued 100nF can be added between VDD and GND for wave filtering."
I use the 1st one, with good results, just adding a pull up resistor ( 10k for me ) and never take care about capacitor.
arssant:
I use the 1st one, with good results, just adding a pull up resistor ( 10k for me ) and never take care about capacitor.
Yes, me too !
arssant:
From adafruit:"Power's voltage should be 3.3 -5.5VDC.
When power is supplied to sensor, don't send any instruction to the sensor within one second to pass unstable status.
One capacitor valued 100nF can be added between VDD and GND for wave filtering."I use the 1st one, with good results, just adding a pull up resistor ( 10k for me ) and never take care about capacitor.
Thanks for info. Had a look at adafruit's website and yes I see that a 10K resistor is recommended. For my knowledge, why 10k instead of 4.7K resistor? In my planned project, 2 of the parameters I wish to monitor on my boat are; humidity/ temp in salon and temp in engine bay - especially for freezing conditions. I had planned to use DHT22 for humidity/temp. Could you please advise a reliable and accurate sensor for the engine bay temp as I note there can be interference in reading multiple sensor data. 
So far I remember 4.7 or 10k pullup resistor should be fine.
2 or more dht22 no problem, connect them on 2 different arduino pin.
Boat... river or sea ?
River no big deal for tiny electronic and sensors.
Sea... take care about salt, as you should know, even you don't get wet whit salty water, every environment exposed piece of electronic is quickly corroded by salt. And I don't know anything about humidity control for this kind of environment.
