Home | Product Categories | Temperature | SEN-10167

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

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.

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.

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?

Is this item currently in stock?

when do you expect these units to be in stock?

Do you think these could be used outside?

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

It’s going to take a while to dig through there… from the datasheet:

“DHT22 send out higher data bit firstly!”

Is there any ETA on this item?

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

Hmm… When did this come in?

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.

This fits in this, yes?

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

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

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

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.

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.

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

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

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

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.

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

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

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.

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.

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…

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

double post deleted

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 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.

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!

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?

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

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?

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 ?

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.