DC Motor Control

The last motor to control for me was a DC motor.

DC stands for direct current which (unlike AC or alternating current) flows in one direction from positive to negative (this comes from conventional current theory).

This diagram displays how an AC motor works

How a DC motor works

With this understanding we can control the direction (anti/clock wise) through which the motor rotates by controlling the currents direction.

We supply the motor from the microchip through the power chip. We take two output pins (digital- on or off or PWM – speed control) and feed them into the H bridge and depending which one you turn on it dictates the directional rotation of the motor.

The speed control aspect is controlling how much current we apply to the motor as we know current is proportional to magnetic flux and also torque.

I initially tested out the motor using a simple on, off, forward and reverse control. I then decided that I wished to use PWM as it required a little more work and will be very useful to me later on with other projects.

The wiring for the Microchip is the same as my other projects ( for the power,control wires from the programmer and switch). The power chip is also the same as that in the stepper motor, but only 2 pins are being fed in and fed out from. (the feed in to the power chip is PWM1H and RD0)

Heres the first PWM code I tested

//
// dsPIC30F4011 Variable Speed Control of A DC motor
// Written by Aisling Lee, Last updated 11-12-2015
//

#include <xc.h>
#include <libpic30.h>
#include <stdio.h>
// Configuration settings
_FOSC(CSW_FSCM_OFF & FRC_PLL16); // Fosc=16x7.5MHz, i.e. 30 MIPS
_FWDT(WDT_OFF); // Watchdog timer off
_FBORPOR(MCLR_DIS); // Disable reset pin

int main(void)
{
 // Setup UART for Machine monitoring
 U1BRG = 48; // 38400 baud @ 30 MIPS
 U1MODEbits.UARTEN = 1; // Enable UART

 // Make RD0 and RD1 digital outputs
 TRISD = 0b1100;

 // Configure PWM
 // PWM period = PTPER * prescale * Tcy = 9470 * 64 * 33.33ns = 20ms
 _PMOD1 = 0; // PWM channel 1 mode: 0 for complementary, 1 for independent
 _PEN1H = 1; // PWM1H pin enable: 1 to enable, 0 to disable
 _PTCKPS = 3; // PWM prescaler setting: 0=1:1, 1=1:4, 2=1:16, 3=1:64
 PTPER = 9470; // Set PWM time base period to 20ms (15-bit value)
 PDC1 = 0; // 0% duty cycle on channel 1 (16-bit value)
 _PTEN = 1; // Enable PWM time base to start generating pulses

while(1)
 {
 if(_RC15 == 1)
 {
 // Forward fast
 PDC1 = 0.75 * 2 * PTPER; // 75% duty cycle
 LATD = 0b01; // forwards
 }

 else
 {
 // Forward slow
 PDC1 = 0.25 * 2 * PTPER; // 25% duty cycle
 LATD = 0b01; // forwards
 }

 }
}

After I got that working I decided to try different speeds (duty cycle percentages ) and give it an application.

I designed a state machine for a variable speed fan. It cycles through OFF, LOW, MEDIUM and HIGH.

//
// dsPIC30F4011 Variable Speed Control of A DC motor
// Written by Aisling Lee, Last updated 11-01-2016
//

#include <xc.h>
#include <libpic30.h>
#include <stdio.h>

// Defining state numbers
#define OFF 0
#define LOW 1
#define MEDIUM 2
#define HIGH 3

// Configuration settings
_FOSC(CSW_FSCM_OFF & FRC_PLL16); // Fosc=16x7.5MHz, i.e. 30 MIPS
_FWDT(WDT_OFF); // Watchdog timer off
_FBORPOR(MCLR_DIS); // Disable reset pin

int main(void)
{
 // Setup UART for Machine monitoring
 U1BRG = 48; // 38400 baud @ 30 MIPS
 U1MODEbits.UARTEN = 1; // Enable UART

 // Make RD0 and RD1 digital outputs
 TRISD = 0b1100;

 // Configure PWM
 // PWM period = PTPER * prescale * Tcy = 9470 * 64 * 33.33ns = 20ms
 _PMOD1 = 0; // PWM channel 1 mode: 0 for complementary, 1 for independent
 _PEN1H = 1; // PWM1H pin enable: 1 to enable, 0 to disable
 _PTCKPS = 3; // PWM prescaler setting: 0=1:1, 1=1:4, 2=1:16, 3=1:64
 PTPER = 9470; // Set PWM time base period to 20ms (15-bit value)
 PDC1 = 0; // 0% duty cycle on channel 1 (16-bit value)
 _PTEN = 1; // Enable PWM time base to start generating pulses

 //my variables
 int ms=30000;
 int cycle=20*ms;
 double second =50*cycle;
 double pause = second;
 int state ;
 _TRISC15 = 1;

 state = OFF;
 while(1)
 {

 if(state == OFF) // Motor Off
 {
 LATD = 0b00; // off
 if(_RD3 == 1) while(_RD3 == 1); __delay32(pause); state = LOW;
 printf("OFF\n"); //monitoring
 }

 if(state == LOW) // Motor slow
 {
 // Forward slow
 PDC1 = 0.25 * 2 * PTPER; // 25% duty cycle
 LATD = 0b01; // forwards
 if(_RD3 == 1) while(_RD3 == 1); __delay32(pause); state = MEDIUM;
 printf("LOW\n"); //monitoring
 }

 if(state == MEDIUM) // Motor medium
 {
 // Forward slow
 PDC1 = 0.5 * 2 * PTPER; // 50% duty cycle
 LATD = 0b01; // forwards
 if(_RD3 == 1) __delay32(pause); state = HIGH;
 printf("MEDIUM\n"); //monitoring
 }

 if(state == HIGH) // Motor fast
 {
 // Forward slow
 PDC1 = 0.75 * 2 * PTPER; // 75% duty cycle
 LATD = 0b01; // forwards
 if(_RD3 == 1) while(_RD3 == 1); __delay32(pause); state = OFF;
 printf("HIGH\n"); //monitoring
 }
 }}

There was a few issues with coding this as the time allowed to press the switch and for it to go to the next state was tricky this you’ll see I’ve implemented loops and delays to try allow enough time for the user to activate the switch. Even then still I found at times the chip operated too fast and I utilized  the UART tool to communicate and let me know as to what state I was in (or getting stuck as it got to a point where I was unable to turn it off) this pointed to as I had previously mentioned the physical speed of the switch not matching that of the code and causes intermittent errors.

Demonstration of a Variable Speed Fan,

As you can see it does not cycle perfectly through the 4 states and at times it is difficult to differentiate between the speeds, that is why I added the LED as it feeds from the PWM1H pin that controls the motor.I spent a long time trying to reduce and eradicate the errors but depending on your speed and how long you hold the switch it does impact the cycles still. I plan to continue looking into this in my own time outside of this project.

After it being pointed out to me that within the if statements (for the switch on RD3) within each of the various states, it was my syntax that was the source of my issue (code cycling through the commands and executing them in an undesired fashion). I altered the code so as it now looks like this,

//
// dsPIC30F4011 Variable Speed Control of A DC motor
// Written by Aisling Lee, Last updated 14-01-2016
//

#include <xc.h>
#include <libpic30.h>
#include <stdio.h>

// Defining state numbers
#define OFF 	0
#define LOW 	1
#define MEDIUM  2
#define HIGH    3

// Configuration settings
_FOSC(CSW_FSCM_OFF & FRC_PLL16); // Fosc=16x7.5MHz, i.e. 30 MIPS
_FWDT(WDT_OFF);                  // Watchdog timer off
_FBORPOR(MCLR_DIS);              // Disable reset pin

int main(void)
{
	// Setup UART for Machine monitoring
    U1BRG = 48;            // 38400 baud @ 30 MIPS
    U1MODEbits.UARTEN = 1; // Enable UART

    // Make RD0 and RD1 digital outputs
    TRISD = 0b1100;

    // Configure PWM
    // PWM period = PTPER * prescale * Tcy = 9470 * 64 * 33.33ns = 20ms
    _PMOD1 = 0;   // PWM channel 1 mode: 0 for complementary, 1 for independent
    _PEN1H = 1;   // PWM1H pin enable: 1 to enable, 0 to disable
    _PTCKPS = 3;  // PWM prescaler setting: 0=1:1, 1=1:4, 2=1:16, 3=1:64
    PTPER = 9470; // Set PWM time base period to 20ms (15-bit value)
    PDC1 = 0;     // 0% duty cycle on channel 1 (16-bit value)
    _PTEN = 1;    // Enable PWM time base to start generating pulses

	//my variables
	int ms=30000;
	int cycle=20*ms;
	double second =50*cycle;
	double pause = second;
	int state ;
	_TRISC15 = 1;

	state = OFF;
	LATD = 0b00;
	printf("START\n"); //monitoring
    while(1)
	{

		if(state == OFF) // Motor Off
        {
			LATD = 0b00;             // off
			if(_RD3 == 1)
			{
				while(_RD3 == 1);
				__delay32(pause);
				state = LOW;
			}
			printf("OFF\n"); //monitoring
		}

		if(state == LOW) // Motor Off
        {
			// Forward slow
			PDC1 = 0.25 * 2 * PTPER; // 25% duty cycle
			LATD = 0b01;             // forwards
			if(_RD3 == 1)
			{
				while(_RD3 == 1);
				__delay32(pause);
				state = MEDIUM;
			}
			printf("LOW\n"); //monitoring
		}

		if(state == MEDIUM) // Motor Off
        {
			// Forward slow
			PDC1 = 0.5 * 2 * PTPER; // 50% duty cycle
			LATD = 0b01;             // forwards
			if(_RD3 == 1)
			{
				while(_RD3 == 1);
				__delay32(pause);
				state = HIGH;
			}
			printf("MEDIUM\n"); //monitoring
		}

		if(state == HIGH) // Motor Off
        {
			// Forward slow
			PDC1 = 0.75 * 2 * PTPER; // 75% duty cycle
			LATD = 0b01;             // forwards
			if(_RD3 == 1)
			{
				while(_RD3 == 1);
				__delay32(pause);
				state = OFF;
			}
			printf("HIGH\n"); //monitoring
		}
	}
}

Here is footage of the new code performing as desired,