DHT Humidity Sensing - Raspberry Pi with Google Docs logging

[discovery]

Does anyone know why I always get at gipo4 20ms low pulse, regardless of whether I have a 100us delay or 500000us? Wathewer i do it does not effect any change? Thank you!

[rtramon]

In the C code in file dht.c the following snippet occurs:

Code: Select all

  // read data!
  for (int i=0; i< MAXTIMINGS; i++) {
    counter = 0;
    while ( bcm2835_gpio_lev(pin) == laststate) {
      counter++;
      nanosleep(1);   // overclocking might change this?
      //delay(1);
      if (counter == 100)
        break;
    }

I do not understand the line nanosleep(1) here, because according to the manual page for nanosleep() it needs two parameters:

Code: Select all

Name

nanosleep - high resolution sleep (REALTIME)
Synopsis

#include <time.h>

int nanosleep(const struct timespec *rqtp, struct timespec *rmtp); 

What is the effect of calling nanosleep(1)?

[netmagi]

New to pi. Trying to get an am2302 (dht22 w/resistor) sensor working and just getting all zeros with the C code from adafruit. Tried compiling my own version with 500ms sleep and it runs (after compiling with errors), but still returns all zeros.

Would someone be willing to share their compiled working C prog?

[Buckers]

I'm no expert and I'm dusting off my C programming skills from over 20 years ago. I have an AM2302 bought from eBay. I got it working by changing the following code block from the orginal ...

Code: Select all

  // Set GPIO pin to output
  bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
  bcm2835_gpio_write(pin, HIGH);
  usleep(500000);
  bcm2835_gpio_write(pin, LOW);
  usleep(20000);
  bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);

So just changed "usleep(500000)" between setting the PIN HIGH and LOW. After compiling the code (running make) it returns good values for me 99% of the time.

[p4trykx]

@Buckers
I changed the sleep time as you suggested an it got big improvement

[kenmc]

I had no problems with the downloaded code from the adafruit website but my humidity is always reading very low - 37% say, when a fine-offset head unit sitting beside it is telling me 57%. Anyone else checked the validity of their data coming from the DTH11?

[kenmc]

I had no problems with the downloaded code from the adafruit website but my humidity is always reading very low - 37% say, when a fine-offset head unit sitting beside it is telling me 57%. Anyone else checked the validity of their data coming from the DTH11?

Actually, perhaps it's right! I just breathed onto the sensor and the humidity went up. A few minutes later, it's back down to 38-39% again, from 65% when I breathed on it. Also, a bit of googling suggests that 30-50 is a normal indoor percentage, so it's spot on there! Happy days!

[discovery]

Thanks to Buckers, now my temperature and humidity reading also works for me.
Can anyone help me with atached error?

Which connection is intendet? If I do not specifie right user name and pass, or spreadsheet key i'll get an error that something is wrong. So i supose that connection to spreadsheet is established.

Thanks in advance!

[p4trykx]

Not sure what you mean. You did specify login and password in Adafruit_DHT_googledocs.ex.py ?
If that's true there could be some problem with logging in to Google. I'm not sure it that's the case but checking your Google account if there isn't any security message about suspicious login.

And maybe first of all check if you have connections to the Internet (i.e. ping google.com)

[discovery]

If i don't specify right username and password I'll get:
"Unable to log in. Check your email address/password"

If i don't specify existing spreadsheet I'll get:
"Unable to open the spreadsheet. Check your filename: %s"

After that (without getting this errors) when the program appends the data to spreadsheet i got an error:
"Unable to append data. Check your connection?"

So if the program recognize the right password and username, and even an existing spreadsheet it must be connected to account?

[kenmc]

If i don't specify right username and password I'll get:
"Unable to log in. Check your email address/password"

If i don't specify existing spreadsheet I'll get:
"Unable to open the spreadsheet. Check your filename: %s"

After that (without getting this errors) when the program appends the data to spreadsheet i got an error:
"Unable to append data. Check your connection?"

So if the program recognize the right password and username, and even an existing spreadsheet it must be connected to account?

A bit leftfield, but are you set up like this :

Pi <-- cable --> Laptop <--wifi---> Internet?

If so, I had the same problem, I managed to get 2 extra, empty rows created in my spreadsheet, but no data in it. Same "couldn't append" lark. I didn't persue it as I'm not looking to use this as a solution. Maybe there's some sort of issue with the connection through the laptop.... anyway, worth a shot...

[discovery]

No, my setup is:
Pi <---cable---> getaway/modem (internet)

So directly to the internet.

[p4trykx]

After my SD Card broke down I installed everything from scratch (latest Wheezy) . Now I get more or less right temperature but the humidity is 99%.
Maybe there where some changes that affected timings?
Or maybe my AM2302 got broken?

[runfastman]

Using a DHT22
I got it to work just the way it was given.
I want to turn stuff on and off according to temperature, so I put the code in an infinite loop.
It works great for 3-8 times and then the application just dies.
In debuging I figured out it is somehere in the "read data!" for loop section, but I can't figure out exactly where or why.

Here is my loop if someone else wants to see if it dies on them.

while (1)
{
printf("Temp Check\n");
readDHT(type, dhtpin);
delay(5000);
}

[pineapple]

Same happened to me. In routine readDHT look for the line:

bits[bitidx++] = counter

and comment it out or delete it. Recompile. This statement was causing a buffer overflow.

Using a DHT22
I got it to work just the way it was given.
I want to turn stuff on and off according to temperature, so I put the code in an infinite loop.
It works great for 3-8 times and then the application just dies.
In debuging I figured out it is somehere in the "read data!" for loop section, but I can't figure out exactly where or why.

Here is my loop if someone else wants to see if it dies on them.

while (1)
{
printf("Temp Check\n");
readDHT(type, dhtpin);
delay(5000);
}

[chorlton2080]

Folks

The code on the Adafruit GIT download source appears to have been modified as per the earlier trials on timing - I had no need to change anything and it works well on a DHT11 - well, it reads and logs on GDocs, I have some suspicion about the humidity readings though from this rather cheap sensor.

Next step is to move data to COSM...

[asa_g]

I've another problem.
Sensor works fine for me about 24 hours and then simply hangs and only power cycle can resolve the problem.
"One capacitor valued 100nF can be added between VDD and GND for
wave filtering." anybody try it?

[asa_g]

new info
sensor stop respond after several hours of work
strace output
"
...
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
nanosleep({0, 1000}, NULL) = 0
...
"
I've made power cycle only for the dht22 and after this it works fine. (but don't know how long)

[technion]

For the dht22, see my other thread, and my version of the app:
http://www.raspberrypi.org/phpBB3/viewt ... 37&t=27215

I've another problem.
Sensor works fine for me about 24 hours and then simply hangs and only power cycle can resolve the problem.
"One capacitor valued 100nF can be added between VDD and GND for
wave filtering." anybody try it?

Where did you see this? I'm always keen to try something that means more soldering..

[asa_g]

https://www.sparkfun.com/products/10167
there are datasheet and example program
yep, i'm using the latest adafruit driver for dht22
i've made changes in my program and now asking dht22 only one time in 15 seconds, may be this will help

[p4trykx]

Maybe there is some counter on the DHT22 which overruns after too many reads and crashes the program on it. Anyways nothing we can do.

[technion]

I've another problem.
Sensor works fine for me about 24 hours and then simply hangs and only power cycle can resolve the problem.
"One capacitor valued 100nF can be added between VDD and GND for
wave filtering." anybody try it?

I've noted that if you google "dht11 capacitor", you land on pages and pages of Aduino users discussing this FAQ around why it is definitely required.

I'll try and get my hands on such a capacitor and report back.

[p4trykx]

In case someone wonders what's inside DHT22

http://dl.dropbox.com/u/96422972/dht22back.JPG

http://dl.dropbox.com/u/96422972/dht22front.JPG

[technion]

Regrettably, no real improvement with the capacitor.

That said, it's about a 5c part, there's kind of no excuse to avoid it.

[technion]

Hey guys,

In line with what I consider important in good coding, there's a new version out.

This one features a method of preventing the app from being run too fast. You can see for example, the results of running it from two terminals within one second of each other. This will ensure that this particular issue isn't involved.

$ sudo /usr/local/bin/loldht
Raspberry Pi wiringPi DHT22 reader
www.lolware.net
Lock file is in use, waiting...
Humidity = 43.60 % Temperature = 25.30 *C

I've included much more stringent checks on return values and type casts, and used "splint" to verify the work.

Finally, there's an autoconf harness.
I haven't seen a dramatic improvement in output reliability, however, it gives us a much more reliable place to go from.