Im building my own watering system and to that I will have some sensores..
They are connected to my pi over SFI and a mcp3008 from Adafruit.
http://www.adafruit.com/products/1989
http://www.adafruit.com/products/856
http://www.kjell.com/sortiment/el/elektronik/elektroniklab/kopplingsplatta-lodfri-p87886
http://www.elecfreaks.com/store/octopus-soil-moisture-sensor-brick-p-422.html
Use this guide and se how the you should connect the mcp3008 and the sensore.
http://www.raspberrypi-spy.co.uk/2013/10/analogue-sensors-on-the-raspberry-pi-using-an-mcp3008/
1. First enable SFI on the board here
http://www.raspberrypi-spy.co.uk/2014/08/enabling-the-spi-interface-on-the-raspberry-pi/
I uses the raspi-config and enabled the SFI
2. Test the SFI
download the tester
wget http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/spi/spidev_test.c -O spidev_test.c
install the dep
apt-get install python-dev
Open the file and change this
static const char *device = "/dev/spidev0.1";
Build it
gcc spidev_test.c
Run it
./a.out
This is what you should see
spi mode: 0 bits per word: 8 max speed: 500000 Hz (500 KHz)
00 02 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Install python and deps
wget https://github.com/Gadgetoid/py-spidev/archive/master.zip unzip master.zip rm master.zip cd py-spidev-master sudo python setup.py install
get my test file to run to see output from alla channels on the mcp3008
https://github.com/mattiashem/r-pi/blob/master/sensor/test.py
The python file will loop over all the channels on you mcp3008 and print the output.