How to generate Pulse Width Modulation (PWM) using PIC microcontroller? This is going to be a continuation of our microcontroller online tutorial series. This article covers the detailed explanation and simulation of PWM generation using PIC16F877A microcontroller.What is a Pulse Width Modulator? A PWM has series of pulses with variable pulse width. We have used Mikro C pro for pic microcontroller programming because it has inbuilt library functions to do many operations especially in PWM, this will simplify the user headache.
The simulation is done with Proteus design suite. In my previous article we have already discussed How to Simulate PIC Microcontroller in Proteus?
PWM has wide applications in automation such as DC motor speed control circuit , generating analog signals from digital signals and LED brightness control.
Before reading PIC PWM please have a look to the following
PWM and PIC
Two CCP module is available with a PIC16F877A MCU. It is capable of generating PWM signals.
MikroC PRO for PIC provides library which simplifies PWM operations. The generated PWM output comes via pin No: 16 and 17 of PIC16F877A microcontroller.
As the name indicates, CCP (Capture Compare PWM) has 3 modes of operation.
- Capture mode
- Compare mode
- PWM mode
In PWM mode PIC can generate signals of varying frequency and duty cycle.
Other modes are beyond the scope of this article. We will discuss those modes later.
Now let’s begin PIC PWM generation!
Add PWM Library to Mikro C
Before writing the program we should add PWM library functions to our code. Otherwise you may be getting compilation errors such as ‘Undeclared identifier PWM1_Init in expression’.
So open ‘Library Manager’ tab and put a check mark on ‘PWM’ library. Then proceed to the program.
PWM Mikro C Program
In this program two input switches are used to control the Duty cycle of PWM signal. S1 for increasing duty cycle and S2 for decreasing the same. Frequency of PWM signal is set to 5KHz[cc lang=”C”]void main()
short duty1 = 16; // initial value for Duty cycle
TRISD = 0xFF; // Set PORTD as input
TRISC = 0x00; // Set PORTC as output
PWM1_Init(5000); // Initialize PWM1 for 5Kh
PWM1_Start(); // start PWM1
PWM1_Set_Duty(duty1); // Set current duty for PWM1
while (1) // endless loop
if (PORTD.F0==0) //Checking the button pressed or not
duty1++; // increment duty cycle
PWM1_Set_Duty(duty1); //Change the duty cycle
if (PORTD.F1==0) // Checking the button pressed or not
duty1–; // decrement duty cycle
Interpretation of important codes
There are two CCP modules inside PIC16F877A. Our program is manipulating the 1st module, thus ‘PWM1′ is used here. ‘_Init’ means initializing the PWM1 for 5KHz.
Start PWM1 signal.
Set current duty cycle for PWM1, using this code we are varying the pulse width.
PWM Simulation in Proteus
Now it’s time to start simulation, the Virtual Lab!
Write the codes in Mikro C and build the .Hex file. If you don’t know how to build hex file please read my article below.
Run Proteus 8 and draw the schematic diagram as shown.
For beginners play the help video tutorial below.
Help Video: Getting Started with Proteus
Load .Hex file for PIC simulation.
Run the simulation.
Enable Digital oscilloscope output by going to Debug >> Digital Oscilloscope and make necessary adjustments for clear view.
Now vary the duty cycle by hitting the keys provided S1 and S2. Below image shows the simulated window of CRO.
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Next >> Pulse width modulation DC motor speed control.
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