Note

Hello, welcome to the SunFounder Raspberry Pi & Arduino & ESP32 Enthusiasts Community on Facebook! Dive deeper into Raspberry Pi, Arduino, and ESP32 with fellow enthusiasts.

Why Join?

• Expert Support: Solve post-sale issues and technical challenges with help from our community and team.

• Learn & Share: Exchange tips and tutorials to enhance your skills.

• Exclusive Previews: Get early access to new product announcements and sneak peeks.

• Special Discounts: Enjoy exclusive discounts on our newest products.

• Festive Promotions and Giveaways: Take part in giveaways and holiday promotions.

👉 Ready to explore and create with us? Click [here] and join today!

2.1.7 Potentiometer(MCP3008)

Note

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

Introduction

The ADC function is used to convert analog signals into digital values. In this experiment, we use the MCP3008 ADC chip to perform this conversion. A potentiometer is used to generate a variable voltage, which changes the physical quantity. The MCP3008 then converts this analog voltage into a digital value that can be read and processed by the Raspberry Pi.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Potentiometer	BUY
MCP3008	-

Schematic Diagram

T-Board Name	physical	WiringPi	BCM
SPICE0	pin24	10	8
SPIMOSI	pin19	12	10
SPIMISO	pin21	13	9
SPISCLK	pin23	14	11
GPIO22	pin15	3	22

Experimental Procedures

Step 1: Build the circuit.

Note

Please place the chip by referring to the corresponding position depicted in the picture. Note that the grooves on the chip should be on the left when it is placed.

Step 2: Set up the SPI interface and install the spidev library (see SPI Configuration for detailed instructions). If you have already completed these steps, you can skip this.

Step 3: Open the code file

cd ~/raphael-kit/python-pi5

Step 4: Run.

sudo python3 2.1.7-2_Potentiometer_zero.py

After the code runs, rotate the knob on the potentiometer, the intensity of LED will change accordingly.

Warning

If there is an error prompt RuntimeError: Cannot determine SOC peripheral base address, please refer to If gpiozero doesn’t work.

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like raphael-kit/python-pi5. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3

import spidev
import time
from gpiozero import PWMLED

# Initialize PWM LED on GPIO22
led = PWMLED(22)

# Initialize SPI
spi = spidev.SpiDev()
spi.open(0, 0)  # Bus 0, CS0 (CE0)
spi.max_speed_hz = 1000000

def read_adc(channel):
    """
    Read analog value from MCP3008
    :param channel: ADC channel (0-7)
    :return: 10-bit integer (0-1023)
    """
    if channel < 0 or channel > 7:
        return -1
    # MCP3008 protocol
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    value = ((adc[1] & 3) << 8) | adc[2]
    return value

def MAP(x, in_min, in_max, out_min, out_max):
    """
    Map a value from one range to another
    """
    return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

try:
    while True:
        # Read from MCP3008 channel 0
        res = read_adc(0)
        print('res = %d' % res)

        # Map 0–1023 to 0–100%
        R_val = MAP(res, 0, 1023, 0, 100)

        # Set LED brightness
        led.value = R_val / 100.0

        time.sleep(0.2)

except KeyboardInterrupt:
    led.value = 0  # Turn off the LED

Code Explanation

1. gpiozero for PWM LED control, spidev for SPI communication with MCP3008, and time for implementing delays.

   #!/usr/bin/env python3
   
   import spidev
   import time
   from gpiozero import PWMLED
   

2. Initialize a PWMLED object connected to GPIO pin 22 and configure SPI communication (Bus 0, CE0) with MCP3008.

   # Initialize PWM LED on GPIO22
   led = PWMLED(22)
   
   # Initialize SPI
   spi = spidev.SpiDev()
   spi.open(0, 0)  # Bus 0, CS0 (CE0)
   spi.max_speed_hz = 1000000
   

3. Define a function named read_adc to communicate with MCP3008 and read analog values from the specified channel (0–7).

   def read_adc(channel):
       """
       Read analog value from MCP3008
       :param channel: ADC channel (0-7)
       :return: 10-bit integer (0-1023)
       """
       if channel < 0 or channel > 7:
           return -1
       adc = spi.xfer2([1, (8 + channel) << 4, 0])
       value = ((adc[1] & 3) << 8) | adc[2]
       return value
   

4. Define a function named MAP to convert one range of values to another, useful for mapping ADC values to appropriate LED brightness levels.

   def MAP(x, in_min, in_max, out_min, out_max):
       return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min
   

5. Continuously read the ADC value in a loop, mapping the 10-bit ADC value (0–1023) to a brightness level (0–100) for the LED. Adjust the LED’s brightness accordingly. Wait 0.2 seconds between each read.

   try:
       while True:
           # Read from MCP3008 channel 0
           res = read_adc(0)
           print('res = %d' % res)
   
           # Map 0–1023 to 0–100%
           R_val = MAP(res, 0, 1023, 0, 100)
   
           # Set LED brightness
           led.value = R_val / 100.0
   
           time.sleep(0.2)
   
   except KeyboardInterrupt:
       led.value = 0  # Turn off the LED