PIC Microcontroller PWM & Timer2 Motor Control Tutorial

Controlling motors is a common requirement in embedded systems. On PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization., timersGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. and PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. (Pulse-Width Modulation) are fundamental features that enable you to drive DC motors, servo motors, or even brushless motors efficiently. In this tutorial, we will explore how to configure timers and generate PWM signals on a PIC microcontrollerIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization. to control motor speed and direction.

Understanding the Role of Timers in Motor Control🔗

Timers in PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization. are hardware modules that increment at a specific rate based on an internal or external clock. By monitoring or comparing the timer value, we can generate precise delays, create periodic interruptsBuilding Real-Time Projects with PIC Using Timer1 and Input CaptureDiscover how to leverage Timer1 and Input Capture on PIC microcontrollers for precise real-time applications, pulse measurements, and periodic interrupts., and produce PWM signals.

Key points about PIC timersGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation.:

• They operate independently of the CPU, allowing the microcontroller to perform other tasksIntegrating Real-Time Operating Systems (RTOS) on PIC32Learn how to effectively integrate an RTOS into your PIC32 project to manage tasks, optimize timing, and maintain real-time, scalable performance. while timing events continue.
• Most PIC MCUsMastering Digital I/O on PIC MCUs with Practical ExamplesLearn hands-on techniques for configuring and using digital I/O pins on PIC microcontrollers to control LEDs, sensors, and more in practical projects. feature multiple timers (e.g., Timer0, Timer1, Timer2, Timer3, etc.), each with different capabilities.
• Often, Timer2 or Timer4 is used in PWM applications because these timers are typically tied to PIC’s capture/compare/PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. (CCP) or enhanced CCP modules.

Pulse-Width Modulation (PWM) Concept🔗

PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. controls the amount of power delivered to a load by varying the relative amount of “on” and “off” times within a given switching period. For motor control, changing the duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. (the percentage of the time the signal is “high”) adjusts the motor’s speed or torque.

A typical PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. signal can be represented as follows:

• Period: The total time for one cycle of the PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. signal.
• Duty CycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation.: The fraction of the period during which the PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. output is high.

Increasing the duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. increases the voltage applied to the motor (on average), thus increasing motor speed.

Configuring Timer2 and PWM Registers🔗

On many PIC devices, Timer2 is commonly used for PWM generation via a CCP (Capture/Compare/PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation.) module. Below is a simplified overview of the relevant registers:

Calculating the PWM Frequency

The PWM frequencyGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. can be calculated (for many PIC MCUs) by:

Where:

• \( F_{\text{OSC}} \) is the PIC clock frequencyLow-Power Strategies: Maximizing PIC Battery LifeDiscover proven low-power strategies for PIC microcontrollers that maximize battery life through smart oscillator use, sleep modes, and efficient coding..
• PrescalerBuilding Real-Time Projects with PIC Using Timer1 and Input CaptureDiscover how to leverage Timer1 and Input Capture on PIC microcontrollers for precise real-time applications, pulse measurements, and periodic interrupts. is configured in T2CON (e.g., 1, 4, 16).
• PR2 is an 8-bit register defining the maximum Timer2 count.

Setting the Duty Cycle

The duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. is set through CCPRxL and the lower bits in CCPxCON. A common formula to determine the duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. register value is:

• The factor of 4 originates from how the PIC hardware organizes the duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. configuration (the DCxB bits in CCPxCON provide fractional duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. adjustments).

Motor Driver and H-Bridge Considerations🔗

While the PIC generates the PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. signal, the microcontroller’s I/O pins alone usually cannot supply enough current to drive motors directly. Thus, you often need:

• A transistor or MOSFET driver for single-direction speed control.
• An H-bridge driver IC (e.g., L293D or a MOSFET-based driver) for full bidirectional speed and direction control.

Ensure to power the motor from a stable power supply and include diodes or integrated flyback protection to safeguard against inductive voltage spikes.

Example: Basic DC Motor Speed Control🔗

Below is an illustrative code snippet in C using the XC8 compilerGetting Started with MPLAB X and the XC8 CompilerSet up MPLAB X IDE and XC8 compiler for PIC programming with our comprehensive guide detailing installation, configuration, and debugging techniques. for a generic PIC, demonstrating Timer2 setup for PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. on CCP1. Adjust register names and bits according to the specific PIC datasheet you are using.

#include <xc.h>
// Example Configuration Bits (adjust to your device and clock):
#pragma config FOSC  = HS     // External High-Speed oscillator
#pragma config WDTE  = OFF    // Watchdog Timer disabled
#pragma config PWRTE = ON     // Power-up Timer enabled
#pragma config CP    = OFF    // Code Protection disabled
#pragma config BOREN = OFF    // Brown-out Reset disabled
#pragma config LVP   = OFF    // Low-Voltage Programming disabled
#pragma config WRT   = OFF    // Flash Program Memory Write disabled
#pragma config CCPMX = RB0    // Example: CCP1 function on RB0 pin
#define _XTAL_FREQ 20000000UL  // 20 MHz external oscillator example
void main(void)
{
    // Set up the PWM pin as output (e.g., CCP1 pin):
    TRISBbits.TRISB0 = 0;  // Example: output on RB0
    // Initialize Timer2 for PWM:
    T2CON = 0b00000101;  // Prescaler = 4 (T2CKPS1:T2CKPS0 = 01), Timer2 ON (TMR2ON = 1)
    PR2   = 124;         // Example PR2 value for ~20 kHz PWM (at 20 MHz clock)
    // Configure CCP1 in PWM mode:
    CCP1CON = 0b00001100; // CCP1 in PWM mode (CCP1M3:CCP1M0 = 1100)
    // Set initial duty cycle ~50%:
    CCPR1L  = 62;         // High 8 bits (PR2 is 124, so 62 is ~50% of 124)
    // CCP1CON lower bits (DC1B1:DC1B0) can fine-tune duty cycle, e.g., 0 for simplicity:
    CCP1CONbits.DC1B = 0;
    // Wait for Timer2 to stabilize:
    __delay_ms(10);
    while (1)
    {
        // Example: ramp duty cycle from ~20% to ~80%
        for (unsigned char duty = 25; duty < 100; duty += 5)
        {
            // Calculate approximate register value for the desired duty cycle:
            unsigned int pwmValue = (unsigned int) (((float)duty/100.0) * (PR2 + 1) * 4);
            // Split into CCPR1L and DC1B bits:
            CCPR1L = (pwmValue >> 2) & 0xFF;
            CCP1CONbits.DC1B = (pwmValue & 0x03);
            __delay_ms(300);
        }
    }
}

Code Highlights

1. PR2 set to 124 generates a PWM period of approximately 20 kHz with a 20 MHz clock and a prescalerBuilding Real-Time Projects with PIC Using Timer1 and Input CaptureDiscover how to leverage Timer1 and Input Capture on PIC microcontrollers for precise real-time applications, pulse measurements, and periodic interrupts. of 4.

2. T2CON sets the prescalerBuilding Real-Time Projects with PIC Using Timer1 and Input CaptureDiscover how to leverage Timer1 and Input Capture on PIC microcontrollers for precise real-time applications, pulse measurements, and periodic interrupts. and turns Timer2 on.

3. CCP1CON configures the CCP1 module for PWMGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. mode.

4. CCPR1L and CCP1CONbits.DC1B define the 10-bit duty cycleGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. value.

Practical Tips🔗

1. Measure the Actual PWM FrequencyGenerating Audio with PIC Timers and PWMExplore how to configure PIC timers and PWM for audio signal generation, including hardware setup, duty cycle adjustments and simple tone creation. with an oscilloscope or frequency counter to verify it matches design goals. Timing inaccuracies can arise from oscillator tolerances or prescalerBuilding Real-Time Projects with PIC Using Timer1 and Input CaptureDiscover how to leverage Timer1 and Input Capture on PIC microcontrollers for precise real-time applications, pulse measurements, and periodic interrupts. usage.

2. Use Proper Bypass Capacitors on the PIC’s VDD pins and motor driver power lines to minimize noise and ripple.

3. Include Flyback Protection such as diode clamps or integrated circuits specifically designed to handle inductive loads.

4. Implement a Ramp or Slew approach (as shown in the example) to smoothly accelerate motors, reducing voltage spikes and mechanical stress.

Conclusion🔗

Using Timers and PWM on PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization. is a straightforward yet powerful technique to drive motors with precision. By configuring Timer2 (or an equivalent timer) and the CCP module, you can produce stable PWM signals to control motor speed under varying loads. Master these fundamental steps-setting the PWM frequency, adjusting the duty cycle, and interfacing with a proper driver-and you will be well on your way to implementing reliable motor control solutions in your own PIC-based projects.