Objective:

Use a raspberry PI to gather and display temperature and humidity data outside my home.

This is a work in progress. My plans include putting the sensor outside via a shielded cable, using a python charting library to visualize the data, and finally making it available via a web server to the computers in my home.

Parts:

• Raspberry Pi model 1G - available from many sources. I purchased mine from Amazon.com

• DHT22 sensor - low cost device to measure temperature and humidity. Also purchased from Amazon.com. The DHT22 is fairly accurate but typified as a slow device. This wasn't a problem for me as I'm only gathering hourly data.

• 4.7K Resistor - 1/8 watt out of my parts stash.

Raspberry PI library:

• You will need to install the CircuitPython-DHT library on your PI to support getting data from the DHT22 sensor.

Software:

Python - I use python to access the data ports on the PI. I'm not particularly good at software, but I do love to code. I created the code below over time. I found lots of references on the web that I learned from.

#Libraries

import adafruit_dht

import board

import os

from datetime import datetime,date

from time import sleep

#initialize sensor

dht = adafruit_dht.DHT22(board.D4)

while True:

dt = date.today()

now = datetime.now()

ct = now.strftime("%H:%M:%S")

try:

temperature = dht.temperature

temperature = (temperature*9/5)+32

humidity = dht.humidity

except:

pass

#do nothing print("error")

f = open("weatherdata.csv", "at")

f.write('%s, %s, %.1f, %.1f\n' % (dt,ct,temperature,humidity))

f.close()

print('%s, %s, %.1f, %.1f' % (dt,ct,temperature,humidity))

if os.path.exists('./getout.txt'):

break

sleep(3600)

Reboot Protection

If the Pi reboots, my program won't start on its own. I searched the web and found a great article about setting up the Pi to boot into a Python script. The author is Scott Kildall and the article is titled, "Raspberry Pi: Launch Python Script on Startup". Check it out, it solved my problem.

Here is a short version of what was needed.

Create a launch script

#!/bin/sh

# launcher.sh

cd /

cd home/pi/weather

sudo python weather.py

cd /

Make the script executable

chmod 755 launcher.sh

Add a link to Crontab to start on reboot

@reboot sh /home/pi/bin/launcher.sh >/home/pi/logs/cronlog 2>&1

Packaging

I developed the project with a small breadboard sitting on top of my Raspberry Pi. After proving the software worked correctly, I fabbed a cable and mounted the Raspberry Pi under the eve of our home.