8. Chapter Potentiometer & LED

Earlier we learned how to use ADC and PWM. In this chapter, we learn to control the brightness of an LED by using a potentiometer.

8.1. Project Soft Light

In this project, we will make a soft light. We will use an ADC Module to read ADC values of a potentiometer and map it to duty cycle ratio of the PWM used to control the brightness of an LED. Then you can change the brightness of an LED by adjusting the potentiometer.

8.1.1. Component List

  1. Raspberry Pi (with 40 GPIO) x1

  2. GPIO Extension Board & Ribbon Cable x1

  3. Breadboard x1

Rotary potentiometer x1

Rotary-potentiometer

Resistor 10kΩ x2

Resistor-10kΩ

ADC module x1 (Only one)

ADC-module-1 or ADC-module-2

LED x1

red-led

Jumper Wire M/M x17

jumper-wire

8.1.2. Circuit with ADS7830

Schematic diagram

ADS7830-Schematic-2

Hardware connection. If you need any support,please feel free to contact us via:

support@freenove.com

ADS7830-fritizing-2

8.1.3. Circuit with PCF8591

Schematic diagram

PCF8591-Schematic-2

Hardware connection.

PCF8591-fritizing-2

8.1.4. Code

8.1.4.1. Python Code Softlight

If you did not configure I2C, please refer to Chapter 7. If you did, please continue.

First, observe the project result, and then learn about the code in detail.

Hint

If you have any concerns, please contact us via: support@freenove.com

  1. Use cd command to enter 08.1.1_Softlight directory of Python code

$ cd ~/Freenove_Kit/Code/Python_GPIOZero_Code/08.1.1_Softlight

  1. Use the python command to execute the Python code “Softlight.py”.

$ python Softlight.py

After the program is executed, adjusting the potentiometer will display the voltage values of the potentiometer in the Terminal window and the converted digital quantity. As a consequence, the brightness of LED will be changed.

The following is the code:

 1#!/usr/bin/env python3
 2########################################################################
 3# Filename    : ADC.py
 4# Description : Use ADC module to read the voltage value of potentiometer.
 5# Author      : www.freenove.com
 6# modification: 2023/05/11
 7########################################################################
 8from gpiozero import PWMLED
 9import time
10from ADCDevice import *
11
12led = PWMLED(17,frequency=1000)      # define LED pin according to BCM Numbering
13adc = ADCDevice() # Define an ADCDevice class object
14
15def setup():
16    global adc
17    if(adc.detectI2C(0x48)): # Detect the pcf8591.
18        adc = PCF8591()
19    elif(adc.detectI2C(0x4b)): # Detect the ads7830
20        adc = ADS7830()
21    else:
22        print("No correct I2C address found, \n"
23        "Please use command 'i2cdetect -y 1' to check the I2C address! \n"
24        "Program Exit. \n");
25        exit(-1)
26        
27def loop():
28    while True:
29        value = adc.analogRead(0)      # read the ADC value of channel 0
30        led.value = value / 255.0      # Mapping to PWM duty cycle       
31        voltage = value / 255.0 * 3.3  # calculate the voltage value
32        print ('ADC Value : %d, Voltage : %.2f'%(value,voltage))
33        time.sleep(0.03)
34
35def destroy():
36    led.close()
37    adc.close()
38    
39if __name__ == '__main__':   # Program entrance
40    print ('Program is starting ... ')
41    try:
42        setup()
43        loop()
44    except KeyboardInterrupt: # Press ctrl-c to end the program.
45        destroy()
46        print("Ending program")

In the code, read ADC value of potentiometers and map it to the duty cycle of the PWM to control LED brightness.

1value = adc.analogRead(0)      # read the ADC value of channel 0
2led.value = value / 255.0      # Mapping to PWM duty cycle