MCP3008 ADC over SPI in Raspberry Pi

Introduction

The MCP3008 chip helps your Raspberry Pi read analog signals by converting them into digital numbers using SPI communication.

You want to read sensor values like temperature or light that give analog output.

You need to measure voltage levels from a device that does not output digital signals.

You want to connect multiple analog sensors to your Raspberry Pi which has no built-in analog input.

You want to build a simple data logger that records analog sensor data.

You want to control devices based on analog sensor readings.

Syntax

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(bus, device)
spi.max_speed_hz = speed

def read_channel(channel):
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    data = ((adc[1] & 3) << 8) + adc[2]
    return data

bus and device specify the SPI bus and device number on Raspberry Pi.

The read_channel function sends commands to MCP3008 and reads the 10-bit analog value.

Examples

Open SPI bus 0, device 0, set speed, read analog value from channel 0, and print it.

Raspberry Pi

spi.open(0, 0)
spi.max_speed_hz = 1350000
value = read_channel(0)
print(value)

Read and print values from all 8 channels of MCP3008.

Raspberry Pi

for ch in range(8):
    print(f"Channel {ch}: {read_channel(ch)}")

Sample Program

This program reads the analog value from channel 0 of the MCP3008 every second and prints it. It closes the SPI connection cleanly when you stop the program.

Raspberry Pi

import spidev
import time

spi = spidev.SpiDev()
spi.open(0, 0)  # Open SPI bus 0, device 0
spi.max_speed_hz = 1350000

def read_channel(channel):
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    data = ((adc[1] & 3) << 8) + adc[2]
    return data

try:
    while True:
        value = read_channel(0)  # Read from channel 0
        print(f"Analog value on channel 0: {value}")
        time.sleep(1)
except KeyboardInterrupt:
    spi.close()
    print("SPI connection closed.")

Important Notes

Make sure SPI is enabled on your Raspberry Pi using raspi-config before running the code.

The MCP3008 has 8 analog input channels numbered 0 to 7.

The returned value is a 10-bit number between 0 and 1023 representing the analog voltage level.

Summary

The MCP3008 lets Raspberry Pi read analog signals using SPI.

Use the spidev library to communicate with MCP3008.

Read analog values by sending commands and interpreting the 10-bit response.