Use Analogue Sensors with Raspberry Pi

Connect an MCP3008 to a Raspberry Pi with a light dependent resistor

Written By: Cherie Tan

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While the Raspberry Pi can control digital inputs and outputs, what if you wanted to read analog signals? 

In this guide, we'll connect up an Analogue to Digital Converter (the MCP3008) to the Raspberry Pi, and then connect a light dependent resistor (LDR) to it. 

Complete this guide to learn how to connect analogue sensors to the Raspberry Pi.

Step 1 Insert the Pi Breakout Board

First, connect the T-Cobbler Plus breakout board to the breadboard.
Attach it so that one side of it is between C1 to C20
Attach the other side so that it is between G1 to G20

Step 2 Insert the MCP3008

Connect MCP3008 to the breadboard. So that one side is between B35 to B42 
The other side should be between F35 to F42
Note: The orientation of the MCP3008 matters here! Make sure that the divot, the little half circle indentation and dot on the MCP3008 is at B35 and F35.

Step 3 Create a 3V3 Power Rail

Connect a Red Jumper Wire between A1 to the Red Power Rail.

Step 4 Create a Ground Rail

Connect a Black Jumper Wire between A5 to the Blue Ground Rail.

Step 5 Extend your Power Rail

Join the gap in your Power rail.

Step 6 Extend your Ground Rail

Extend your Ground Rail

Step 7 Connect VDD to Power Rail

Run a Red Jumper Wire from G35 to the Power Rail to connect the MCP3008's VDD to power.

Step 8 Connect VREF to Power Rail

Run a Red Jumper Wire from G36 to the Power Rail to connect the MCP3008's VREF to power.

Step 9 Connect Analogue Ground to Ground Rail

Run a Black Jumper Wire from G37 to the Ground Rail to connect the MCP3008's Analogue Ground to Ground.

Step 10 Connect CLK to GPIO18

Run a Yellow Jumper Wire from G38 to J6 to connect the MCP3008's CLK to GPIO18.

Step 11 Connect Digital Out to GPIO23

Run a Green Jumper Wire from G39 to J8 to connect the MCP3008's Digital Out to GPIO23.

Step 12 Connect Digital In to GPIO24

Run a Blue Jumper Wire from G40 to J9 to connect the MCP3008's Digital In to GPIO24.

Step 13 Connect CS/SHDN to GPIO25

Run another Yellow Jumper Wire from G41 to J11 to connect the MCP3008's CS/SHDN to GPIO25.

Step 14 Connect Digital Ground to Ground Rail

Run a Black Jumper Wire from G42 to the Ground Rail to connect the MCP3008's Digital Ground to Ground.

Step 15 Insert 10k resistor

Insert a 10K Ohm Resistor with one leg in H55 and the other in H58.

Step 16 Insert Photo Resistor

Insert a 10K Ohm Photo Resistor with one leg in G52 and the other in G55.

Step 17 Connect Photo Resistor to Ground

Run a Black Jumper between F52 and Ground to connect the Photo Resistor to Ground.

Step 18 Connect 10K Resistor to Power Rail

Run a Red Jumper between F58 and Power to connect the Resistor to the Power Rail.

Step 19 Connect Voltage Divider to Analogue In of MCP3008

Run a Green Jumper between F55 and D35 to connect the Voltage Divider to Analogue Channel 0 of the MCP3008.

Step 20 Start up the Raspberry Pi

With a NOOBS microSD card, start up your Raspberry Pi and install Raspbian. Please follow our previous guide on doing just that if you are unsure how to. Alternatively, you could create your own NOOBS microSD card.

Step 21 Install GPIO Zero library

Now that the Raspberry Pi is connected to the Analogue to Digital Converter and light dependent resistor, we will program it. Let's install GPIO Zero, a Python library which builds upon existing GPIO libraries such as RPI.GPIO, rPIO, and pigpio. It helps to simplify the process by reducing boilerplate code. 
First, open a terminal window by clicking on the terminal icon on the top left hand corner. 
Type the following: sudo apt-get update 
Install GPIO Zero library using: sudo apt-get install python3-gpiozero

Step 22 Start IDLE

Click on the Raspberry Pi icon on the top left hand corner to access the main menu. 
Click on Programming > Python 3 (IDLE). 
Create a new file by clicking File > New File. 
Next, save the file by clicking File > Save, and naming it

Step 23 Code

from gpiozero import MCP3008
from time import sleep

ldr = MCP3008(channel=0, clock_pin=18, mosi_pin=24, miso_pin=23, select_pin=25)

while True:
Copy and paste the following code.
Save the file
Note: The gpiozero library provides two SPI implementations, a software based implementation or a hardware based implementation. So the MCP3008 can be connected to the Raspberry Pi either with the hardware SPI bus, or with any four GPIO pins and software SPI to communicate to the MCP3008. In this guide, we've chose to use software SPI.

If you want to try using hardware SPI, make sure the connections are:

VDD (Pin 16) wire this to 3.3V
VREF (Pin 15) wire this to 3.3V
AGND (Pin 14) wire this to ground
CLK (Pin 13) wire this to GPIO11 (Pin 23/SCLK)
DOUT (Pin 12) wire this to GPIO9 (Pin 21/MISO)
DIN (Pin 11) wire this to GPIO10 (Pin 19/MOSI)
CS (Pin 10) wire this to GPIO8 (Pin 24/CE0)
DGND (Pin 9) wire this to ground

Next, make sure SPI is enabled over in Raspberry Pi Configuration > Interfaces.

Then, swap the existing line of code with this instead:

ldr = MCP3008(channel=0, clock_pin=11, mosi_pin=10, miso_pin=9, select_pin=8)

Step 24 Test it out

It should return a read value from the device scaled to a value between 0 and 1.
Open a terminal window and type: sudo python
Try covering the light-dependent resistor. The value being outputted will vary with light intensity.