Ran into issues using the example code and library on mesh particle devices (argon, boron) and had luck with DHT22Gen3_RK particle library. Might be applicable for other particle devices that do not allow the applications to fully disable interrupts.

-------------------- Tech Support Tips/Troubleshooting/Common Issues --------------------

Example Tutorial

Garage Lab Tutorial: Humidity and Temperature Sensor with Arduino http://garagelab.com/profiles/blogs/tutorial-humidity-and-temperature-sensor-with-arduino

Multiple RHT03/DHT22 Sensors on Arduino

Theoretically, you should be able to add more than one RHT03/DHT22 sensor to an Arduino. The sensor uses only one I/O pin. By connecting additional RHT03/DHT22 sensor to another I/O pin, redefining the pin to the respective RHT03/DHT22 sensor, and calling new instances of the RHT03/DHT22 library, you should be able to theoretically have multiple RHT03/DHT22 sensors on Arduino. I haven't fully tested this out with multiple sensors but I was able to compile a modified example for two sensors without any issues.

Here's an example with Multiple Sensors with Arduino for illustration => [ http://diy-scib.org/blog/multiple-dht-humidity-sensors-arduino ].

Awesome data sheet!!
Now I know how to use it...

Just tried a whole lot of different libraries and this is the one that works the best so far : http://learn.adafruit.com/dht

Nice sensor. I've been using it to monitor
a greenhouse for about two months. The wet
environment doesn't seem to have harmed it.
Temperature is accurate, and humidity seems
about right - I think I believe this more
than I do the other humidity sensors in
there. I'll be buying more.

Nice little hook-up guide here:

http://garagelab.com/profiles/blogs/tutorial-humidity-and-temperature-sensor-with-arduino

I was using NetHoncho's library, and was getting only maybe one out of ten readings correct. The rest were sync timeout errors.
I modified his library to retry up to 70 times instead of 35 times, and that did the trick. Look for this line in his lib:
if (retryCount > 35) //(Spec is 50 us, 352 == 70 us)
-- and change it to this --
if (retryCount > 70) //(Spec is 50 us, 352 == 70 us)
Thanks for the lib NetHoncho! Works great now.

It does't exsit RHT03 or DHT22 version. RHT03 and DHT22 are two different names for one same product.
We have three names for this product, the names are RHT03 DHT22 AM2302. So, be noted that you are using the same product.
I have asked our engineer to recheck if RHT03/DHTT22 could work under 3.3V DC this morning, the answer is RHT03/DHT22 could work properly under power supply of 3.3V DC.
I think you have to check if the power supply at RHT03's power pin is >=3.3V DC.

Don't bother trying to run the RHT03 at less than 5 volts.
It doesn't report the humididty correct at the 3.46 I said it was giving me values at..
Glenn

I just found the same thing to be true that the RHT03 version does not work for 3.3V. They do work for the 5V..
I am going to contact sparkfun tec support and see if they have the DTH22 version hanging around so I can complete my project 3.3v.
By the way did some testing and the DTH22 reports back at 3.1 volts just not sure how accurate didn't have anything handy to check the temp or humidity against.

I created an Arduino library for the DHT22 http://goo.gl/uy1fV

Hello!

I am trying to interface DHT22 with ATmega128RFa1 but having an issue. I am suspecting that the sensor is not responding to the MCU's request signal. After I send the request signal to the sensor, I wait for 10 ms for the sensor to detect the request. Then the sensor should respond driving the signal from low to high, right? I guess I am not getting this correct. Are there any other things that I should be considering besides timing?

Any help would be appreiciated. Cheers!!

Pretty good sensor for temperature and humidity. Successfully interfaced it to an 8051 port pin. Had to use a logic analyzer for accurate timing constraints and implementation. However, it's easy to work with ... Check out the project if you'd like to see this interfaced with an 8051 using SDCC compiler. https://github.com/pswapnil/ZigBeeTempSensor

Everyone who hates the one-wire interface raise your hand! Especially when they have 4 pins anyway. You can have I2C for that.

I purchased it and I want to use it with Arduino Due but it is not work, with same program and same connection it works well with UNO. I used 3.3volt as input .. with same power it works with arduino DUE... any suggestion????

Here's another implementation for reading out the sensor:

https://github.com/liyanage/maxdetect-rht03-humidity-sensor/

I'm running it on a Spark Core board and I have a Google Drive spreadsheet that automatically pulls and logs the values every 10 minutes. I'll be hooking it up to a solid state relay to control a humidifier next.

I'd like to use this sensor in a very high humidity, 70%RH at minimum I figure .. I saw in the datasheet that it says Avoid using the sensor under dew condition. Does this mean that this sensor should only be used for a short amount of time under very "dewey" conditions?

Thanks!

Hello, Has anyone used this sensor on TelosB / Tmote Sky nodes? Thanks

Some notes:

the DHT library works best.

The humidity sensor on this thing appeared to have crapped out after two weeks worth of use - simply reads 99.9% for the RH.

This communication scheme is also pretty sensitive to electrical noise. I had a DC motor running in it's vicinity, and it was pretty much un-readable.

The datasheet states that the RHT03 can be used with 3.3 to 6V. Is anyone successful in using RHT03 sensors with 3.3V power? I have a breadboard prototype with multiple RHT03 sensors and an Arduino Pro Mini powered via an FTDI Basic board. The sketch is a modification of the DHT library from Adafruit. When using a 5V/16Mhz Arduino Pro Mini the sketch outputs apparently valid humidity and temperature values for all sensors. However, after replacing the Pro Mini with the 3.3V/8MHz version (Vcc = 3.26V actual) the software reports values of 0.0 for humidity and temperature for all sensors. I have tried: 1) using 1K, 10K or no pullup resistors, 2) 100nF caps across sensor Vcc-GND, or none, 3) connecting both sensor pins 3 & 4 to GND. With any of these changes the reported values remain at 0.0. Maybe the signal timing needs to be tweaked for 3.3V??

Any reason why this sensor indicates 20% humidity (outside), while different weather stations shows 60% humidity for the same location? Temperature is correct.

Does anyone know where I can find an Eagle library for this part? Thanks!

So do you have to connect the null pin to anything? I'm confused what this is for. Trying to learn electronics.

Had 2 of these sensors sitting around for a project I just now started getting time to make, and ATM I'm able to get acceptable values at @3.3v using a FreeSOC mini, the only issue I have is that my calculated checksum value is does not match the broadcast-ed check sum value,

Hi, i have this sensor in my bath. the problem is that the humidity changed with a small wind and it take time to make it stable again. do you know way? thanks kobi.

I have been really impressed with this sensor. I did not believe they could possibly deliver the datasheet's quoted accuracy at this price. You can spend thousands on a lab-grade hygrometer and they still only claim 2% accuracy. How can this do it for $10? So I tried to test and compare six of them for my myself. I do not claim to be an expert or that this experiment is flawless, but if anyone is interested my write up is at http://www.kandrsmith.org/RJS/Misc/calib_dht22.html These are just the results I got for my devices. At the level of errors I am seeing, the fault could just as likely be in my experiment as in the devices themselves.

I still do not really believe the 2% absolute accuracy claim from 0-100%, but they are amazingly good for the price and come surprisingly close to that. The maximum errors I have measured are about 6% RH, with typical errors of 2-3% RH. I see quite a strong temperature dependence of at least 2% RH over the temperature range I have tested so far but am still working on that. I have not done any long term tests, but on timescales of a few weeks I find repeatability in the range 0.5-1% RH.

Hi All, I trying to read from DHT22 sensor. Now I get following code: 4 198 0 246 192 CRC code is right, temperature is right but humidity is wrong (4 and 198 means 1222). In my opinion it seems that there are a shit error in the High Humiditi data (4) instead of 2. But how is it possibile if I get the right CRC code? please, help me. I'm using voltage supply of 3.3V.

Hi - I'm trying to get this going on an OMAP3 system using a standard GPIO. I can't find any code base that isn't Rpi or Arduino. Does anyone have any code that can be used on a general linux system?

Thanks!

It looks like a tiny breadboard!

few observations to those who are experiencing random errors (sync timeout, bus hang etc.) with any of Arduino libraries:

1. USE 5V Power Supply rather than 3V
2. Triple check your Pin Headers are perfect, or better - solder the DHT22 pins directly to Arduino pins or the PCB
3. Use this library which doesn't fail after changing serial baud rates, is small and fast

several weeks of tests led me to the single conclusion - this chip is very sensitive to poor contacts. Where the standard i2c devices work smoothly, DHT22 fails on the same connectors. Have no oscilloscope, can't explain why.

If you want to use this with Raspberry Pi, Gordon over at wiringpi.com has added maxdetect support to his wiringpi arsenal. I got this working today fairly easily with that. http://wiringpi.com/dev.

Here is the quick program. Make sure to compile with something like "gcc rht.c -o rht -lwiringPi -lwiringPiDev"

Also note that I had to take out the chevrons in the #include lines for some reason to get those headers to show up

#include wiringPi.h
#include maxdetect.h
#include stdio.h
#include stdlib.h
#include stdint.h
#include time.h

int main() {
  int myTemp        = 0;
  int myRelHumidity = 0;
  int attempts      = 5;
  int goodReading   = 0;

  if (wiringPiSetup () == -1) {
    printf("\n\nERR: setup for wiringPi failed\n\n");
    exit (1);
  }

  while (!goodReading && (attempts-- > 0)) {
    usleep(1000*10);
    if (readRHT03 (15, &myTemp, &myRelHumidity) 
      //keep looping and try again
    } else {
      goodReading = 1; // stop now that it worked
    }
    usleep(1000*500);
  }

  printf("Temp: %2.1fF  ",(((((float)myTemp/10)*9)/5)+32));
  printf("RH: %2.1f%%\n",((float)myRelHumidity/10));

  return 0;
}

I purchased this sensor a few weeks ago. I was able to get up and running in a short amount of time using a UNO and the RHT03 library from adafruit. However, it appears that only the first few reads of the sensor are accurate. The sensor seems to be self heating at about 0.5 degrees C every 30 seconds. I am only reading every 30 seconds thinking that increasing the time between reads would reduce the self heating. Any suggestions?

Matt

Is this device support UART/USART communication?? may i connect this device with Xbee??

Anyone have any luck getting this to run with a Raspberry Pi? If so please share you code and schematic.

Thx Rich

I try this sensor with NetHoncho library but it always return Checksum error. I change the setup, with/without resistor, reading 40 instead of 41 and always the same result.

It works for me with the code from arduino playground http://playground.arduino.cc/Main/DHTLib I just change the delay to 2000 and move this to the begining of the loop, and remove the code for the DHT11

How do I use this sensor in Arduino 1.0.1 ?

I have had the RHT03 working for about 3 months, but now the humidity reads 1.0% but the temperature is working correctly. Has the device gone bad? Has anyone else had this problem?

As a beginner, it's been a bit of a pain for me to get this thing working with an Arduino Uno R3. The datasheet and example code are hard to follow, but the discussion here has been quite helpful.

If you're coming up with code to read data from the sensor yourself, consider that the timings mentioned in the datasheet are not quite right. Basically, what you can count on is that the zero-bit pulse is a fair bit shorter than the one-bit pulse. If you're code makes too many assumptions about the timing, you might get out of sync with the incoming signal.

Here's my code for my Uno. YMMV, of course. It prints out humidity and temp readings every 5 seconds to the serial console. Seems reliable on my system; no failures in the last couple hours it's been running.

Does this work OK outdoors?

Great sensor although the datasheet is something out of a science fiction novel written in engrish. nethoncho / Arduino-DHT22 is a great resource to get you up and running in seconds. Watch out for the legs, very delicate!

Works nicely with my Uno R3 and compares really well to my wall mount commercial product I used to check the values with but when running with small (remote mounted) battery which is being charged by small solar panel, the values begin to deviate quite a lot with the voltage.

Any ideas how to stabilize this component without a small nuclear plant for steady supply?

IMHO: I would NOT use this sensor for outdoor humidity because dew will be seen by the sensor and degrade it's readings. Many commercial weather stations have this as a small foot note in their documentation. Which seems to be kind of silly, "Don't put your outdoor humidity sensor "outdoors" because it may see dew and degrade it performance"!?!?! What? How stupid is that? What does this all mean? If you use THIS sensor outdoors, after some period of time your humidity/dew point values will start to go wacky and have to be compensated for. (Speaking from experience with a commercial weather station.) After reviewing the other humidity sensors on SF, it seems they do not have this problem. Thus use this sensor indoors only.

NOTE: In the data sheet it males a reference to dew conditions: (7) Other attentions * Avoid using the sensor under dew condition.

Had some trouble getting this sensor to work with my Uno. I finally was able to get it to work by using this library: http://arduino.cc/playground/Main/DHTLib I did have to change the baud rate to 9600.

I then attached the sensor to 3.3V, Gnd, and Digital Pin 5

I did not need a resistor or capacitor to allow this sensor to return reasonable results without error.

Sensor is not not working further than 120cm. Sensor works in about 80cm temperature & humidity are correct. But any cable further to 120cm doesn't work. The cable itself is Ok - tested with Serial LCD. It works. What can be the problem?

I spent about 9 hours bashing my head against this sensor (or, well, the wall while trying to get this sensor working) before finally getting it going. Write-up and sample code here

Key lessons:

• When requesting a sensor read, you have to actively pull the signal line high after your initial 1 - 10ms low pulse. Stopping pulling it low and letting a pull-up resistor bring it high is not good enough, at least with my setup (tried 20k built-in and 1k external pull-up resistors). You must actively pull the line high (+5V DC) for 20-40us then let the pull-up take over and wait for the it to go low as the sensor ACKs your request.
• The datasheet is a lie. In particular, instead of a neat 50us low signal before sending a bit, my sensor may pull the line low for anything from 35 to 75us. Similarly, 0-bit high pulses may be from 10-40us instead of the documented 22-26us, and 1-bit high pulses may be 60-85us instead of 70us.
• Even when you're being tolerant of timing weirdness, you'll get bad reads. Adding a cap across the +5VDC input (as mentioned in the datasheet) doesn't seem to help, so it's probably not power fluctuation. Be prepared to re-try reads and remember to wait at least 2s between reads.
• (Didn't trouble me, but): Remember to let the sensor settle for at least 2s after power-on before attempting a read, and at least 2s between reads.

Running into a bit of trouble hooking one of these up to an UNO. I've tried the NetHoncho and adafruit libs with no result. The NetHoncho lib gives me an "ACK time out"

Any thoughts on how to continue ?

Just got one of these,

Temperature reading seems accurate. RH is way off. at least 20% off.

What could I have done wrong? Is the sensor bad? I'm reading it with check-sum, so it is not likely a data interpretation issue.

From reading other comments it seems like I am not the only one seeing this type of behavior. Is this just a crappy sensor? the datasheet does indicate that it goes to as much as +- 5% at the edges, but +- 20% is utterly useless.

Any ideas?

It works almost perfect but.....

The temperature reports good results but the humidity is a little bit strange. It reports 29,70 29,80 29,90 30,00 99,99 I looks to me that there is some timing error or is it that I destroyed the sensor when I tryed out the 1K resistor as pullup instead of the 4K7 ? //Mats

Not sure why the example code for this product is in Microsoft Word (.doc) RTF format which can likely lead to corrupted characters and formatting issues? Why not share it using a Github Gist?

Here's an example of working code with the Arduino. The example polls every 6 seconds or so, and gives you humidity and temperature readings.
http://sheepdogguides.com/arduino/ar3ne1humDHT11.htm
Works a treat!

I got two of these few days ago. During the weekend I wanted to see how it worked. Connected pin 1 to 5V, pin 2 with 1K resistor to 5V, pin 3 and 4 to GND. Connected an oscilloscope to pin 2 and briefly brought pin2 to ground. I can see the rising edge, but just a flat solid 5V (i.e. high bit). I tried to pilot it using a digital line from a Flyport, but got same results. I tried to use the second RHT03 that I got, same behavior. Looks like they are not working. Any suggestions on what I'm doing wrong or how can I check if they are working? Thanks a lot.

I'm having a fair amount of problems with this product.
I'm using this library:
http://arduino.cc/playground/Main/DHTLib
And I'm trying to pull the information from the DHT22, and send it to a Pachube feed, once a minute.
I split up the calls for the current temperature and humidity. Each request is 30 seconds apart. However, I'm still getting a rate of around 45% checksum errors. I'm also occasionally getting spurious temperatures in the 55f(12c) range. My lab is pretty steady around 74-79f.
I've only had the chip for a week (today), and I'd really like to get this project completed (I've already gotten a couple requests for new unit builds). Am I asking too much of the sensor? Does anyone know of a method for reducing errors?
I'm using a resistor on the dataline, as specified. I put in a filtering cap, but didn't see any improvement with the error rate.

I was never able to get the sensor that I had running at 3.3v but Thomas sent me photos of the RHT03 running at 3.3v, I will assume it is something with the batch.
I will use the two I have up for a 5v project and wait for the a new batch to arrive and try the new batch at 3.3v. Looks like Sparkfun only has one left at the moment so shouldn't be too long

Thomas
I understand what you are saying that they should be one and the same but they are not. The ones I am calling DHT22 were bought from sparkfun at the first of the year and match the picture above and will run at 3.18 volts(battery was getting low) and report correctly.
The one I am calling RHT03 has that with the MaxDetect logo on the bottom of it and were bought in July from sparkfun. It will not run at 3.31 or 3.46 volts correctly, measured at the vcc pin for the sensor.
I checked voltage using an ideal 61-361 meter.
I even reset up the original bread board that I had, and used sparkfun's FTDI break out board for power. the 5 volt version the RHT03 and DHT22 works, for the 3.3 volt version only the DHT22 work. I then hooked up a lipo for power putting it through a N4001 diode the voltage was 3.46 and the temp was right but the humidity was a little over double on the RHT03 the DHT22 reported correctly. I am using a ATMEL ATMega328P with ardiuno boot loader on some PCB I had made and the bread boards using Ben Adams version 4 DHT22 library.
The Temp and Humidity values are checked against a sensiron SHT15 on another bread board using a arduino boot loaded Atmega32p with the sensiron SHT15 library.
I have 3 more PCB boards that I need to populate and run at 3.3 volts so I am looking for some DHT22, I am going to use the RHT03 that I have for some green house controls I am going to make but they will be run at 5 volts so wont be an issue.
Plain and simple I can't get the last shipment to run at the same voltage the original ones I bought run at using the same set up...

It does't exsit RHT03 or DHT22 version. RHT03 and DHT22 are two different names for one same product.
We have three names for this product, the names are RHT03 DHT22 AM2302. So, be noted that you are using the same product.
I have asked our engineer to recheck if RHT03/DHTT22 could work under 3.3V DC this morning, the answer is RHT03/DHT22 could work properly under power supply of 3.3V DC.
I think you have to check if the power supply at RHT03's power pin is >=3.3V DC.

To add one more final thing I found that the RHT03 does seem to work at 3.46 volts, Close to the upper end of where my 3.3 volt LCD is not going to be happy. I hope they fix this issue and get the sensor back to what the DHT22 was doing.
Glenn

Thanks, Babcoccl, all good now - had a bad 5v connection. Accuracy within 0.5 degree C; pretty good for $10.
Cheers; Dave

I wonder if this can be adapted to the Peet Bros weather stations?

Thanks to NetHoncho for the library and code - a great help. Have hooked the sensor up as suggested but just get this error: "Requesting data... ACK time out". Does anyone have any ideas how to overcome this?
Cheers;
Dave

Can anyone help me?
I have try to follow the connection on data sheet.
But the Data pin always high.
What can I do for testing? Thank You.

Can I place multiple DHT22s on the same wire and address them individually?
I know Maxim can handle this and I'd like to minimize the pins used for this on my Arduino as I'd like to put as many as 10 on my system, but I don't see where it states this capability for this version of 1-wire.

Could I read the output from this sensor with just an XBee, without connecting an Arduino or microcontroller?

Hey,
How does this compare to Sensiron's offerings? I have a SHT21 and a DHT22 on my desk connected to a PIC.
The temperatures are within a degree of each other, but the RH is ~30% out (SHT reads 34%, DHT reads 65%).
Obviously there is a price difference between the two but both claim to be calibrated etc.
Neither has undergone recent soldering, so I would have thought the humidity sensor has settled.
Any ideas?
Steaky

PICAXE 18M2 - Has anyone interfaced this sensor to this, who can give me a leg up as to how to do the communications code please? Pity its not Ascii or something more standard

This fits in this, yes?

I made some code and have been polling this with my ARMmite at 1 s intervals (using C, not BASIC). But while at first it seemed to work correctly, now it is returning 0 as the checksum (still giving numbers that seem correct for the Humidity and Temp though).... Odd.

Hmm... When did this come in?

Is there any ETA on this item?

It's going to take a while to dig through there... from the datasheet:

"DHT22 send out higher data bit firstly!"

The first time I saw it, I thought it was a pico breadboard with just 3 rows of 5 holes (and some mysterious slots)!

Do you think these could be used outside?

when do you expect these units to be in stock?

Is this item currently in stock?

Is the interface compatible with 1-wire interface? The data sheet discusses the 1 data line, but it isn't clear that it is 1-wire as defined by Maxim/Dallas. Does anyone know?