User manual

Example Projects

2.3.5 Project 5: Brushed DC Motor Speed Control with Optical

Encoder Feedback

Motor control is required in many mechatronic applications ranging from power

windows to washing machine cycle control. This project will demonstrate speed control

of a Brushed DC motor. Brushed DC motor control is simple as the commutation, or

sequencing of power to the various windings, is automatically performed by the motor’s

brushes. In this project, the Capture Compare PWM (CCP) module will be used in

PWM mode to generate a Brushed DC motor drive. Timer1 will measure speed

feedback from the optical interrupter on the board. The optical interrupter circuit

generates a high signal when light passes through the slots in the encoder disk. By

measuring the time between pulses, the speed of the motor can be determined. A

real-life application example includes precision speed control of a fan or hard disk

drive.

Objectives

1. Configure the CCP module to generate a PWM signal.

2. Use a PWM signal to vary the speed of a Brushed DC motor.

3. Configure Timer1 to use the optical interrupter as its clock source.

Applicable Technical Documents

Brushed DC Motor Fundamentals Application Note, AN905 (DS00905)

Low-Cost Bidirectional Brushed DC Motor Control Using the PIC16F684 Application

Note, AN893 (DS00893)

Jumper Configuration

• RD7 (J10) to P1 (J1)

• CCP2 (J10) to N2 (J1)

• AN0 (J13) to POT1 (J4)

• RC5 (J10) to Optical Interrupter (J7)

• Attach the motor leads to DRIVE1 (P9) and DRIVE2 (P10).

• J2 and J3 should be unpopulated (no shunts present).

• Connect the right and center pins of JP8 using a shunt.