Controlling LED with PIC Microcontroller using LDR

• PIC16F8778 PIC microcontroller
• 20 MHz crystal oscillator
• 22 pF capacitors
• 5 mm LED
• LDR sensor
• Breadboard
• Jumper wires

1. Place the PIC microcontroller on the breadboard.
2. Connect pin 11 of the PIC to the positive terminal of the breadboard.
3. Connect pin 12 of the PIC to the negative terminal of the breadboard.
4. Connect pin 31 of the PIC to the negative terminal of the breadboard.
5. Connect pin 32 of the PIC to the positive terminal of the breadboard.
6. Connect the crystal oscillator between pins 13 and 14 of the PIC.
7. Connect a 22 pF capacitor between the negative terminal of the breadboard and the crystal oscillator.
8. Connect a 10 kOhm resistor between pin 1 of the PIC and the positive terminal of the breadboard.
9. Connect one terminal of the LDR sensor to the positive terminal of the breadboard.
10. Connect a 10 kOhm resistor between the negative terminal of the breadboard and the other terminal of the LDR sensor.
11. Connect the LDR terminal to analog pin A0 of the PIC microcontroller.
12. Connect the negative terminal of the LED to the negative terminal of the breadboard.
13. Connect the positive terminal of the LED and pin 1 of port B of the PIC through a 220 ohms resistor.

1. Open Micro C Pro and create a new project.
2. Enter the project name, device name, and frequency of the crystal oscillator.
3. Create a new project and enter the code:

// Define LED pin at RB1
#define LED_PIN TRISBbits.TRISB1

// Define LDR threshold
#define LDR_THRESHOLD 512

// Configure analog to digital converter settings
void configADC() {
  ADCON = 0x80; // Set ADC on and configure settings
}

// Initialize ports and variables
void init() {
  LED_PIN = 0; // Set LED pin as output
  TRISBbits.TRISB1 = 0; // Set direction of pin RB1 as output
  configADC(); // Configure ADC settings
}

// Main program loop
while(1) {
  // Read analog value from channel 1 using ADC
  signed int LDR_value = ADC_Read(1);
  
  // Check if light level is low (below threshold)
  if(LDR_value < LDR_THRESHOLD) {
    LED_PIN = 1; // Turn on LED
  } else {
    LED_PIN = 0; // Turn off LED
  }
  
  // Add a delay of 500 milliseconds before the loop ends
  __delay_ms(500);
}

1. Open PickKit 2 software.
2. Erase the chip.
3. Import the hex file created in Micro C Pro.
4. Upload the program to the PIC microcontroller.

Controlling LED with PIC Microcontroller using LDR

In this article, we will explore how to control an LED using a PIC microcontroller and a Light Dependent Resistor (LDR). The LDR is used as a sensor to detect the light intensity and based on that, the LED is turned ON or OFF.

Hardware Components

• PIC Microcontroller (e.g., PIC16F877A)
• LDR (Light Dependent Resistor)
• LED (Light Emitting Diode)
• Resistors (1kΩ, 10kΩ)
• Breadboard and Jumper Wires

Circuit Diagram

The LDR is connected to the PIC microcontroller's analog input pin (AN0). The LED is connected to one of the digital output pins (RB0) through a resistor. A voltage divider circuit is formed using two resistors (1kΩ and 10kΩ) to provide a reference voltage for the ADC.

Software Components

• MPLAB X IDE (or any other PIC microcontroller programming software)
• PIC16F877A Library (for ADC and Digital I/O functions)

Code Explanation

The code starts by configuring the PIC microcontroller's ADC module and setting the reference voltage. Then, it reads the analog value from the LDR using the ADC module.

        #include <xc.h>
        
        // Configuration bits
        __CONFIG(FOSC_INTOSC & WDTE_OFF & PWRTE_OFF & MCLRE_OFF & CP_OFF & BOREN_OFF & IESO_OFF & FCMEN_OFF);
        
        // Function to read analog value from LDR
        unsigned int read_ldr(void) {
          ADCON0bits.ADON = 1;  // Turn ON ADC module
          __delay_ms(10);      // Wait for ADC to settle
          ADCON0bits.GO_DONE = 1;  // Start conversion
          while (ADCON0bits.GO_DONE);  // Wait for conversion to complete
          return ADRES;            // Return the result
        }
        
        void main(void) {
          TRISBbits.RB0 = 0;      // Set RB0 as digital output
          PORTBbits.RB0 = 0;     // Initialize LED as OFF
        
          while (1) {
            unsigned int ldr_value = read_ldr();
            
            if (ldr_value > 512) {  // If light intensity is high
              PORTBbits.RB0 = 1;   // Turn ON LED
            } else {
              PORTBbits.RB0 = 0;   // Turn OFF LED
            }
          }
        }
      

Working Principle

The LDR's resistance changes in response to the light intensity. When the light intensity is high, the LDR's resistance decreases and vice versa. The PIC microcontroller reads this change in resistance using its ADC module and converts it into a digital value.

Based on the digital value, the PIC microcontroller controls the LED connected to one of its digital output pins. If the light intensity is high (i.e., LDR's resistance is low), the LED is turned ON; otherwise, it remains OFF.

• 8-bit microcontroller with 14KB of program memory
• 256 bytes of EEPROM data memory
• 368 bytes of RAM
• 20 MHz clock frequency

• Resistance range: 100 ohms to 1M ohm
• Sensitivity: 10-20% per 10 lux change in light intensity
• Power dissipation: 0.25W

• Forward voltage: 1.8-2.2V
• Reverse voltage: 5V
• Current: 20mA
• Luminous intensity: 1000-2000 mcd

• Tolerance: ±5%
• Power dissipation: 0.25W

        LIST p=16F877A
        INCLUDE <p16F877A.inc>
        
        __CONFIG _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOREN_OFF & _IESO_OFF & _FCMEN_OFF
        
        ORG 0x00
        GOTO MAIN
        
        MAIN
            BSF STATUS, RP0 ; Select Bank1
            CLRF ANSEL    ; Configure PortA as digital I/O
            BCF STATUS, RP0 ; Select Bank0
            
            MOVLW 0xFF    ; Initialize PORTB as output
            MOVWF TRISB
            
            LDR_LOOP
                MOVLW 0x00    ; Read LDR value
                MOVWF ADCON0
                
                BSF ADCON0, GO ; Start conversion
                BTFSS ADCON0, DONE ; Wait for conversion complete
                
                MOVF ADRESH, WREG ; Get result
                SUBLW 0x10      ; Subtract threshold (adjust as needed)
                
                BTFSC STATUS, CARRY
                    BSF PORTB, 0   ; Turn on LED if LDR value is below threshold
                ELSE
                    BCF PORTB, 0   ; Turn off LED otherwise
                ENDIF
                
                GOTO LDR_LOOP
        
        END