DC motor Speed control using pic microcontroller

This tutorial is about dc motor speed control with a pic microcontroller using the PWM method. There are many applications of DC motors, where we need a variable speed of DC motor. For example, it has applications in electric cars, trucks, and aircraft. These are three examples where we need variable speed. Although nowadays AC motors have more use in the market for variable speed applications over DC motor due to enhancement in power electronics and solid-state electronics. But,  direct current rotational machines are still used today in many applications for variable speed requirements.

Types of DC motors

According to armature and field current circuit configuration, there are five types of DC motor:

• DC motor with separate excitation
•  Shunt Type
• Series
• Compound ( Series+shunt)
•  With excitation from a permanent magnet

The speed of separately excited DC motor and DC shunt motor can be made variable by changing terminal voltage and by changing the armature resistance. The speed of the DC series motor and permanent magnet DC motor can only be changed by changing the armature terminal voltage. Conversely, the Compound  DC motor has both characteristics of DC series motor and DC shunt motor.

How to Control DC Motor Speed?

First of all,  there is one features common in all types of DC motors. The rate of acceleration depends on the magnitude of the armature terminal voltage. Therefore, We can use this common feature to control speed. Speed control by changing armature terminal voltage is the same in all types of DC motors.  In short, we can apply the same method to all direct current rotational machines.

At the start, to make this project possible, we have to learn a method through which we can apply variable DC voltage to the armature of any DC motor. Thereafter, we can control the speed of DC motor according to our requirements.

Methods to generate a variable armature voltage

We can generate variable dc voltage by two methods. Firstly, we will discuss the variable power supply method. After that, we will briefly go through the pulse width modulation technique.

Variable Power Supply Method

In variable power supply technique, there are some limitations. But we can still use it for small power DC motors.  It can be controlled by making a variable power supply with the help of voltage regulators. They are capable to generate variable voltage within a specified limit provided by the manufacturer. There are many voltage regulators in the market. But there will be an issue of the current rating of DC motor. Because power supplies that make with such voltage regulators have not too much high power handling capability. A power supply is the main source of power to DC motor. Therefore this method is not practically feasible and recommended. This technique is costly also.

Pulse Width Modulation Technique

On the contrary, pulse width modulation is the best method to control DC voltage applied to the terminal of the armature. In pulse width modulation,  we actually control the switching duty cycle, which is the ratio of on-time to the total time of switching.

PWM for DC Motor Speed Control

PWM Introduction

This is a method to control the output voltage with constant frequency switching and by adjusting on the duration of switching and in other words by changing the duty cycle of switching.

Constant switching time period = on time + off time                                                                              
Duty Cycle = (on time / on time + off time ) %

The duty cycle can not be greater than 1 or 100%. Because on time will always be less than the total time period of switching frequency. The relationship of input-output voltage and the duty cycle is

output voltage =  duty cycle * input voltage

Hence the output voltage and duty cycle is directly related to each other. However,  their output also depends on switching frequency of switch. What is a switch here. I will discuss it later.

In the above picture, there are four PWM having different duty cycles. Therefore,  we need to change the duty cycle according to the requirement of the output voltage. But output voltage can never be greater than the input voltage.  At last, if you have still trouble in grasping these concepts, read this complete guide:

• introduction to pulse width modulation

PWM Generation Methods

But now the question which must come into mind. How to generate PWM and how to use PWM for variable output voltage generation?  At the present time, there are two ways to generate pulse width modulation with variable duty cycle:

1. Using analog electronics ( operational amplifier, comparator and sawtooth wave, etc)
2. Using digital electronics  ( microcontrollers and dedicated PWM controllers IC’s )

We will not discuss the first method in this article. but in future, we will write a complete post on Pulse width modulator using analog electronics. But those who don’t know about programming and microcontrollers can use analog electronics methods for this purpose.

Dc Motor Speed Control  using pic microcontroller

To control DC motor speed with  PIC microcontroller, we should know about these two features:

• how to generate PWM using PIC microcontroller
• how to use the analog channel of PIC microcontroller to read analog voltage.

If you don’t know about these topics. Kindly visit the following link to get the understanding of PIC microcontrollers and PWM programming.

• PWM using pic microcontroller
• Analog voltage measurement using pic microcontroller

As we mentioned earlier,  there are two methods to make a pulse width modulator. These are the analog Electronics method and the digital Electronics method using Microcontrollers.

Dedicated PWM controller ICs for Speed control

There are dedicated PWM controller IC’s are also available in the market like SG3525, UC3842, SG2525, and many others. These PWM controller IC’s also use analog electronics methods. Because their internal circuitry consists of operational amplifiers, resistors, and capacitors. I will write also write an article on PWM controllers for those who hate programming and don’t know about the use of Microcontrollers. But there are few issues with these ready to use PWM controller IC’s. A most important issue is:

1. you will require many extra components to make them ready to use.
2. The exact frequency is not achievable. 1-2% error
3. There is also a frequency limitation which in some cases generates audible in motors.

But there are no such issues with pulse-width modulators of digital electronics type.

DC Motor Speed Control Circuit diagram

We have used PIC16F876 microcontroller to generate PWM and to change the duty cycle by reading the analog value of voltage across the variable resistor. we can use any microcontroller you want. But logic will remain the same.

In the above circuit diagram,  12v is used as a power source.7805 voltage regulator is used to provide 5 volts to variable resistor and supply to microcontroller. There is no need to give supply 5 volts in Proteus to a microcontroller. Because by default 5 volt and ground have been supplied to the microcontroller in Proteus. A variable resistor is used to change the duty cycle of PWM. By moving the knob of a variable resistor you can change the duty cycle which is directly related to the speed of the DC motor. Therefore,  we can adjust the speed of the DC motor by adjusting the variable resistor knob according to your speed requirement.

Video Lecture Demonstration

The PWM frequency is about 8Khz which will not make any audible noise. You can adjust it according to your motor specifications. IRL1004 is used as a switch. IRL1004 FET requires the only 5-volt logic level driver to operate FET and a negligible amount of current. Therefore there is no need for any driver to drive IRL1004 FET. It can handle more than one-ampere current very easily as it is mentioned in its datasheet. Diode 1N4007 is used as a freewheeling fast recovery diode. Because the motor is an inductive load and its back emf may damage the circuit. Freewheel diode will provide flow path to back emf current and avoid sparking across motor terminals.

Other DC Motor Projects

• PIC to PIC SPI communication with DC motor control
• Bluetooth based dc motor speed and direction control using Arduino

Code for speed control of dc motor

long ADCValue=0;
long ADCValueOld=1;

#byte portA = 0X05
#byte portB = 0X06
#byte portC = 0X07

void main()
{
set_tris_A(0b00101011);
set_tris_B(0b00000001);
set_tris_C(0b00000000);

portA=0X00;
portB=0X00;
portC=0X00;

setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_INTERNAL);
setup_spi(FALSE);
setup_counters(RTCC_INTERNAL,WDT_288MS);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);
setup_timer_2(T2_DIV_BY_1,255,1);
setup_ccp1(CCP_OFF);
setup_ccp2(CCP_PWM);
enable_interrupts(global);

set_adc_channel(0);
delay_us(10);

while(1)
{
ADCValue = Read_ADC();
delay_ms(100); // monitor 10 times a second

if ( ADCValue != ADCValueOld )
{
set_pwm2_duty(ADCValue);
ADCValueOld = ADCValue;
}
}
}

If you want to learn to program of PWM and ADC (analog to digital converter) using PIC Microcontrollers. Check PIC microcontroller tutorials.

• PIC Microcontrollers Tutorials
• PIC microcontroller Projects 

If you want complete simulation and code of this project. Comment on this post with your email address and if you have any issue while making this project, feel free to comment on this post.

Future Recommendations

1. Feedback control mechanism to ensure constant speed
2. Direction control of DC motor using H bridge
3. Try to control more than one motor.
4. Final year projects: Speed control of DC motor through wireless communication like GSM, GPRS, Bluetooth, ZigBee, and many other wireless communication techniques.