Wiring the Raspberry Pi to an I2C device
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
12May20  Everett Lipman


NOTE: I2C is the Inter-Integrated Circuit serial data bus,
      over which the RPi communicates with sensor devices.
      I2C is widely used for this purpose, for example in
      many cars.


1. Make sure you can read the diagram below.  If not, download
   it from here:

http://web.physics.ucsb.edu/~phys129/lipman/handouts/i2c/mcp9808_wiring.jpg

   It is the last link at the bottom of the Handouts page.

2. Shut down your RPi and ***UNPLUG the power cable from the RPi!***

3. Align the RPi so that the two rows of GPIO connectors
   are at the upper right, as in the picture.  The picture
   shows an older version of the RPi, but the GPIO
   connections we will use are the same.

4. Turn your I2C device so that the part number printed
   on the board (MCP9808 or ADS1015) is properly oriented,
   and the pins are facing away from you.

5. At the lower left of the I2C device, identify the following pins:

   1. Vdd: the positive power supply for the board (must be +3.3 V)
   2. GND: common ground for the power supply, clock, and data lines
   3. SCL: the I2C clock line, which synchronizes the RPi with the device
   4. SDA: the data transfer line

6. Locate the 4-wire cable from your hardware kit.
   Everyone has different colors, so you should decide
   which color will correspond to each line.







7. Using the 4 wires, connect the RPi pins shown in the diagram to
   the corresponding pins on the board.  *** DO THIS CAREFULLY! ***
   If you power up with the wrong pins connected, you can destroy
   your RPi.

   In particular, be certain you are using the 3.3 V pin
   on the upper left of the two rows of pins, NOT the 5 V
   pin at the upper right.  Also, BE CERTAIN you have not
   connected the 3.3 V or 5 V pins to ground!

8. If you are using the ADS1015, get the solar cell from
   your hardware kit.  Identify the positive wire on the
   back of the solar cell, and connect it to pin A2 on
   the ADS1015.  Connect the negative wire to pin A3.
   If you place the solar cell in direct sunlight while
   it is connected to the ADS1015, you could destroy the
   board, so avoid this.

9. Check your connections.  Once you are absolutely
   sure you have wired the correct pins on the RPi to the
   corresponding pins on the board, check your connections.

10. Now you've got to ask yourself one question: "Do I feel
    lucky?"  Regardless of the answer, check your
    connections.  When you feel you can no longer take
    the pressure, take a deep breath and check your
    connections.  Then plug in and boot up your RPi.

11. If your RPi boots up, you have not destroyed it.
    Be careful not to let the I2C device board pins touch
    anything conductive.

12. If you are using the MCP9808, run tempdemo.py from the
    course Python directory.  If you are using the ADS1015,
    run adcdemo.py.  If you see a series of temperature or
    voltage readings, congratulations!  You have correctly
    connected the I2C device.