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Connecting the Cobbler to a MCP3008 Created by MikeySklar

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To follow this tutorial you will need

MCP3008 DIP-package ADC converter chip10K trimer or panel mount potentiometerAdafruit Pi Cobbler - follow the tutorial to assemble itHalf or Full-size breadboardBreadboarding wires

And of course a working Raspberry Pi with Internet connection

Why we need an ADC

The Raspberry Pi computer does not have a way to read analog inputs. It's a digital-onlycomputer. Compare this to the Arduino, AVR or PIC microcontrollers that often have 6 or moreanalog inputs! Analog inputs are handy because many sensors are analog outputs, so we need away to make the Pi analog-friendly.

We'll do that by wiring up an MCP3008 chip to it. The MCP3008 acts like a 'bridge' betweendigital and analog. It has 8 analog inputs and the Pi can query it using 4 digital pins. That makesit a perfect addition to the Pi for integrating simple sensors like photocells, FSRsor potentiometers, thermistors, etc.!

Lets check the datasheet of the MCP3008 chip. On the first page in the lower right corner there'sa pinout diagram showing the names of the pins

Wiring Diagram

In order to read analog data we need to use the following pins: VDD (power), DGND (digitalground) to power the MCP3008 chip. We also need four 'SPI' data pins: DOUT (Data Out fromMCP3008), CLK (Clock pin), DIN (Data In from Raspberry Pi), and /CS (Chip Select). Finally ofcourse, a source of analog data, we'll be using the basic 10k trim pot.

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The MCP3008 has a few more pins we need to connect: AGND (analog ground, used sometimesin precision circuitry, which this is not) connects to GND, and VREF (analog voltage reference,used for changing the 'scale' - we want the full scale so tie it to 3.3V)

Below is a wiring diagram. Connect the 3.3V cobbler pin to the left + rail and the GND pin to theright - rail. Connect the following pins for the MCP chip

MCP3008 VDD -> 3.3V (red)MCP3008 VREF -> 3.3V (red)MCP3008 AGND -> GND (black)MCP3008 CLK -> #18 (orange)MCP3008 DOUT -> #23 (yellow)MCP3008 DIN -> #24 (blue)MCP3008 CS -> #25 (violet)MCP3008 DGND -> GND (black)

Next connect up the potentiometer. Pin #1 (left) goes to GND (black), #2 (middle) connects toMCP3008 CH0 (analog input #0) with a gray wire, and #3 (right) connects to 3.3V (red)

Advanced users may note that the Raspberry Pi does have a hardware SPI interface (the cobblerpins are labeled MISO/MOSI/SCLK/CE0/CE1). The hardware SPI interface is super fast but notincluded in all distributions. For that reason we are using a bit banged SPI implementation so theSPI pins can be any of the raspberry pi's GPIOs (assuming you update the script).

< Overview Necessary Packages >

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Last updated on 2012-07-20 at 08.33.52 PM

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