DHT2302 Sensor
Moderators: adafruit_support_bill, adafruit

Forum rules
Talk about Adafruit Raspberry Pi® accessories! Please do not ask for Linux support, this is for Adafruit products only! For Raspberry Pi help please visit: http://www.raspberrypi.org/phpBB3/
Please be positive and constructive with your questions and comments.

Re: DHT2302 Sensor

by thogue on Wed Oct 24, 2012 3:43 pm

Afternoon everyone,

First, I thought I would chime in here, I have the dht2302 working great on my pi, It took lots of playing with in order to get it to read properly. I recompiled the C code to exclude the prints except the Temp / Humidity line, this made working with it in python a little easier on me, for efficiencies sake this might not be the best. I had trouble recompiling and after a little research, this solved my error
Code: Select all | TOGGLE FULL SIZE
gcc -l rt Adafruit_DHT.c -l bcm2835 -std=gnu99 -o Adafruit_DHT

my python code runs the c app to get the data,
writes it to the lcd,
sleeps 2 seconds.

if data is not received, it sleeps for .05 and tries again. So far the most failures in a row I've seen is 3. Timing seems very important when reading the sensor. I have played with the sleeps in my program for a bit, and this is the best results I have gotten so far.

here is my code for anything that might want to take a look, most of the code was taken from adafruits examples. (Thanks again Adafruit)

Code: Select all | TOGGLE FULL SIZE
   from Adafruit_CharLCD import Adafruit_CharLCD
   from subprocess import *
   from time import sleep, strftime
   #from datetime import datetime

   lcd = Adafruit_CharLCD()

   # Returns a strink containing Temp / Humidity seperated by a space
   cmd = "/root/tempclock/Adafruit_DHT 2302 4 | awk -F' ' '{ print $3\" \"$7'}"


   def run_cmd(cmd):
      p = Popen(cmd, shell=True, stdout=PIPE)
      output = p.communicate()[0]
      return output

   while 1:
      temps = run_cmd(cmd)
      # Handle misreads properly, this setting seems to be best of both worlds quick/reliable
      while temps == "":
         print "sleeping .05, didnt read"
         temps = run_cmd(cmd)
      temp, humid = temps.split()
      temp = 9.0 * float(temp) / 5.0 + 32
      print "Temp: " + str(temp) + "F Humidity: " + str(humid)
      # Prevent lcd curruption, while lcd is clearing
   #       lcd.message(datetime.now().strftime('%b %d  %H:%M:%S\n'))
   #       lcd.message('Temp: ' + str(temp) + 'Hum: ' + str(humid) + '%'  )
      lcd.message('Temp: ' + str(temp) + 'F\n')
      lcd.message('Hum: ' + str(humid) + '%')     
except KeyboardInterrupt:
Posts: 3
Joined: Mon Oct 15, 2012 11:22 pm

Please be positive and constructive with your questions and comments.