13. Chapter Motor & Driver

In this chapter, we will learn about DC Motors and DC Motor Drivers and how to control the speed and direction of a DC Motor.

13.1. Project Control a DC Motor with a Potentiometer

In this project, a potentiometer will be used to control a DC Motor. When the Potentiometer is at the midpoint position, the DC Motor will STOP, and when the Potentiometer is turned in either direction of this midpoint, the DC Motor speed increases until it reached the endpoint where the DC Motor achieves its maximum speed. When the Potentiometer is turned “Left” of the midpoint the DC Motor will ROTATE in one direction and when turned “Right” the DC Motor will ROTATE in the opposite direction.

13.1.1. Component List

Breadboard Power Module

Raspberry Pi (with 40 GPIO) x1
GPIO Extension Board & Ribbon Cable x1
Breadboard x1

Jumper Wires x23

jumper-wire

Breadboard Power Module x1

9V Battery (you provide) & 9V Battery Cable

Battery_cable

ADC module x1

or

L293D IC Chip

DC Motor x1

Rotary Potentiometer x1

Resistor 10kΩ x2

13.1.2. Component knowledge

13.1.2.1. Breadboard Power Module

Breadboard Power Module is an independent circuit board, which can provide independent 5V or 3.3V power to the breadboard when building circuits. It also has built-in power protection to avoid damaging your RPi module. The schematic diagram below identifies the important features of this Power Module:

Here is an acceptable connection between Breadboard Power Module and Breadboard using a 9V battery and the provided power harness:

13.1.2.2. DC Motor

DC Motor is a device that converts electrical energy into mechanical energy. DC Motors consist of two major parts, a Stator and the Rotor. The stationary part of a DC Motor is the Stator and the part that Rotates is the Rotor. The Stator is usually part of the outer case of motor (if it is simply a pair of permanent magnets), and it has terminals to connect to the power if it is made up of electromagnet coils. Most Hobby DC Motors only use Permanent Magnets for the Stator Field. The Rotor is usually the shaft of motor with 3 or more electromagnets connected to a commutator where the brushes (via the terminals 1 & 2 below) supply electrical power, which can drive other mechanical devices. The diagram below shows a small DC Motor with two terminal pins.

When a DC Motor is connected to a power supply, it will rotate in one direction. If you reverse the polarity of the power supply, the DC Motor will rotate in opposite direction. This is important to note.

13.1.2.3. L293D

L293D is an IC Chip (Integrated Circuit Chip) with a 4-channel motor drive. You can drive a Unidirectional DC Motor with 4 ports or a Bi-Directional DC Motor with 2 ports or a Stepper Motor (Stepper Motors are covered later in this Tutorial).

Port description of L293D module is as follows:

Pin name	Pin number	Description
In x	2, 7, 10, 15	Channel x digital signal input pin
Out x	3, 6, 11, 14	Channel x output pin, input high or low level according to In x pin, getsconnected to +Vmotor or 0V
Enable1	1	Channel 1 and Channel 2 enable pin, high level enable
Enable2	9	Channel 3 and Channel 4 enable pin, high level enable
0V	4, 5, 12, 13	Power Cathode (GND)
+V	16	Positive Electrode (VCC) of power supply, supply voltage 4.5~36V
+Vmotor	8	Positive Electrode of load power supply, provide power supply for the Out pin x, the supply voltage is +V~36V

13.1.3. Circuit with ADS7830

Use caution when connecting this circuit because the DC Motor is a high-power component. Do not use the power provided by the RPi to power the motor directly, as this may cause permanent damage to your RPi! The logic circuit can be powered by the RPi’s power or an external power supply, which should share a common ground with RPi.

Schematic diagram

Motor-ADS7830-Sc

Hardware connection. If you need any support,please feel free to contact us via:

support@freenove.com

Motor-ADS7830-Fr

13.1.4. Circuit with PCF8591

Use caution when connecting this circuit because the DC Motor is a high-power component. Do not use the power provided by the RPi to power the motor directly, as this may cause permanent damage to your RPi!` The logic circuit can be powered by the RPi’s power or an external power supply, which should share a common ground with RPi.

Schematic diagram

Motor-PCF8591-Sc

Hardware connection. If you need any support,please feel free to contact us via:

support@freenove.com

Motor-PCF8591-Fr

13.1.5. Code

In code for this project, first read the ADC value and then control the rotation direction and speed of the DC Motor according to the value of the ADC.

13.1.5.1. C Code Motor

If you did not configure I2C, please refer to Chapter 7. If you did, please continue.

First, observe the project result, and then learn about the code in detail.

Hint

If you have any concerns, please contact us via: support@freenove.com

Use cd command to enter 13.1.1_Motor directory of the C code.

$ cd ~/Freenove_Kit/Code/C_Code/13.1.1_Motor

Use the following command to compile Motor.cpp and generate the executable file Motor.

$ g++ Motor.cpp -o Motor -lwiringPi -lADCDevice

Then run the generated file Motor.

$ sudo ./Motor

After the program is executed, you can use the Potentiometer to control the DC Motor. When the Potentiometer is at the midpoint position, the DC Motor will STOP, and when the Potentiometer is turned in either direction of this midpoint, the DC Motor speed increases until it reaches the endpoint where the DC Motor achieves its maximum speed. When the Potentiometer is turned “Left” of the midpoint the DC Motor will ROTATE in one direction and when turned “Right” the DC Motor will ROTATE in the opposite direction. You will also see the ADC value of the potentiometer displayed in the Terminal with the motor direction and the PWM duty cycle used to control the DC Motor’s speed.

The following is the code:

/**********************************************************************
* Filename    : Motor.cpp
* Description : Control Motor by L293D
* Author      : www.freenove.com
* modification: 2020/03/09
**********************************************************************/
#include <wiringPi.h>
#include <stdio.h>
#include <softPwm.h>
#include <math.h>
#include <stdlib.h>
#include <ADCDevice.hpp>

#define motorPin1    2        //define the pin connected to L293D
#define motorPin2    0
#define enablePin    3

ADCDevice *adc;  // Define an ADC Device class object

//Map function: map the value from a range to another range.
long map(long value,long fromLow,long fromHigh,long toLow,long toHigh){
    return (toHigh-toLow)*(value-fromLow) / (fromHigh-fromLow) + toLow;
}
//motor function: determine the direction and speed of the motor according to the ADC 
void motor(int ADC){
    int value = ADC -128;
    if(value>0){
        digitalWrite(motorPin1,HIGH);
        digitalWrite(motorPin2,LOW);
        printf("turn Forward...\n");
    }
    else if (value<0){
        digitalWrite(motorPin1,LOW);
        digitalWrite(motorPin2,HIGH);
        printf("turn Back...\n");
    }
    else {
        digitalWrite(motorPin1,LOW); 
        digitalWrite(motorPin2,LOW);
        printf("Motor Stop...\n");
    }
    softPwmWrite(enablePin,map(abs(value),0,128,0,100));
    printf("The PWM duty cycle is %d%%\n",abs(value)*100/127);//print the PMW duty cycle
}
int main(void){
    adc = new ADCDevice();
    printf("Program is starting ... \n");

    if(adc->detectI2C(0x48)){    // Detect the pcf8591.
        delete adc;                // Free previously pointed memory
        adc = new PCF8591();    // If detected, create an instance of PCF8591.
    }
    else if(adc->detectI2C(0x4b)){// Detect the ads7830
        delete adc;               // Free previously pointed memory
        adc = new ADS7830();      // If detected, create an instance of ADS7830.
    }
    else{
        printf("No correct I2C address found, \n"
        "Please use command 'i2cdetect -y 1' to check the I2C address! \n"
        "Program Exit. \n");
        return -1;
    }
    wiringPiSetup();
    pinMode(enablePin,OUTPUT);//set mode for the pin
    pinMode(motorPin1,OUTPUT);
    pinMode(motorPin2,OUTPUT);
    softPwmCreate(enablePin,0,100);//define PMW pin
    while(1){
        int value = adc->analogRead(0);  //read analog value of A0 pin
        printf("ADC value : %d \n",value);
        motor(value);        //make the motor rotate with speed(analog value of A0 pin)
        delay(100);
    }
    return 0;
}

Now that we have familiarity with reading ADC values, let’s learn the subfunction void motor (int ADC): first, compare the ADC value with 128 (value corresponding to midpoint). When the current ADC value is higher, motoRPin1 outputs high level and motoRPin2 outputs low level to control the DC Motor to run in the “Forward” Rotational Direction. When the current ADC value is lower, motoRPin1 outputs low level and motoRPin2 outputs high level to control the DC Motor to run in the “Reverse” Rotational Direction. When the ADC value is equal to 128, motoRPin1 and motoRPin2 output low level, the motor STOPS. Then determine the PWM duty cycle according to the difference (delta) between ADC value and 128. Because the absolute delta value stays within 0-128, we need to use the map() subfunction mapping the delta value to a range of 0-255. Finally, we see a display of the duty cycle in Terminal.

void motor(int ADC){
    int value = ADC -128;
    if(value>0){
        digitalWrite(motorPin1,HIGH);
        digitalWrite(motorPin2,LOW);
        printf("turn Forward...\n");
    }
    else if (value<0){
        digitalWrite(motorPin1,LOW);
        digitalWrite(motorPin2,HIGH);
        printf("turn Back...\n");
    }
    else {
        digitalWrite(motorPin1,LOW); 
        digitalWrite(motorPin2,LOW);
        printf("Motor Stop...\n");
    }
    softPwmWrite(enablePin,map(abs(value),0,128,0,100));
    printf("The PWM duty cycle is %d%%\n",abs(value)*100/127);//print the PMW duty cycle
}