PIC PWM Motor Driver

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Contents

Overview

This motor controller was designed for use as cheap, simple motor controller for brushed DC motors. It uses a PIC Microcontroller to convert a low-power analog control signal to a PWM duty cycle which is amplified using a full-bridge to drive a motor. A block diagram of this is shown below. This document gives the circuitry and programming needed to make such a controller.

PIC PWM block.png

PIC PWM

The first thing you need is a PIC microcontroller set up to convert an analog input to a PWM signal. The PIC used here is the PIC16F684. It only has one input, the analog control signal. It has two outputs: two opposite pulse width modulated pulse trains. The two PWM signals activate the two halves of the H-bridge to control the direction of the motor.

PIC Code

Code can be downloaded here.

The zip file contains the following files:

  • main.asm - the program
  • macros.inc - contains macros (quick code)
  • PIC16F684.INC - assigns names to register addresses
  • PICPWM.mcw and PICPWM.mcp - MPLAB workspaces

Circuit

The circuit consists of the PWM-enabled PIC chip, an amplifier and some protection circuitry. There are two versions of the circuit, one for low-power motors (1A continuous) and one for high-power motors (4A continuous).

Low Power

The low-power circuit uses the L293B push-pull driver (datasheet).


High Power

Signal Conditioner (Optional)

Using with PC/104

TO DO

  1. Add "brake" functionality to the PIC. This will require at least one additional input. For example, a single digital input pin could #:cause the motor to "brake" when it's set high. To "brake", the PIC will have to disable the PWM mode and set the two output pins equal #:to eachother.
  1. Add "sensing" capability for better control.
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