Arduino - Motor PID Speed Control

Link to purchase:

1. Motor with encoder: https://amzn.to/2NwsNxH

2. H-bridge: https://amzn.to/2QS2FeI

3. Arduino Pro Mini: https://amzn.to/2xy4yFn

Buy electronic component on utsource.net

Introduction

With PID control, the speed of a motor can be archived exactly. This article mainly introduces making a program for the Arduino Pro Mini on your computer (using Visual Studio) to control motor speed by a PID algorithm.

The Arduino Pro Mini is used to store motor controls, PID algorithms, and to communicate with the PC (through COM Port). The computer should have HMI made by Visual Studio to communicate with Arduino. HMI will show motor speed graphs and change motor speed settings.

Let's go into detail.

Hardware needed:

1. Motor with Encoder

2. H-bridge PCB

3. Arduino Pro Mini

4. UART PCB

5. Computer (with Visual Studio)

Step 1. Hardware connection

This article doesn't mention connection details; it is based on a previous article which can be found at this link.

Step 2. Code with the Arduino

void loop() {
   if (stringComplete) {
     // clear the string when COM receiving is completed
     mySt = "";  //note: in code below, mySt will not become blank, mySt is blank until '\n' is received
     stringComplete = false;
   }
  //receive command from Visual Studio
   if (mySt.substring(0,8) == "vs_start"){
     digitalWrite(pin_fwd,1);      //run motor run forward
     digitalWrite(pin_bwd,0);
     motor_start = true;
   }
   if (mySt.substring(0,7) == "vs_stop"){
     digitalWrite(pin_fwd,0);
     digitalWrite(pin_bwd,0);      //stop motor
     motor_start = false;
   }
   if (mySt.substring(0,12) == "vs_set_speed"){
     set_speed = mySt.substring(12,mySt.length()).toFloat();  //get string after set_speed
   }
   if (mySt.substring(0,5) == "vs_kp"){
     kp = mySt.substring(5,mySt.length()).toFloat(); //get string after vs_kp
   }
   if (mySt.substring(0,5) == "vs_ki"){
     ki = mySt.substring(5,mySt.length()).toFloat(); //get string after vs_ki
   }
   if (mySt.substring(0,5) == "vs_kd"){
     kd = mySt.substring(5,mySt.length()).toFloat(); //get string after vs_kd
   } 
 }
void detect_a() {
   encoder+=1; //increasing encoder at new pulse
   m_direction = digitalRead(pin_b); //read direction of motor
 }
 ISR(TIMER1_OVF_vect)        // interrupt service routine - tick every 0.1sec
 {
   TCNT1 = timer1_counter;   // set timer
   pv_speed = 60.0*(encoder/200.0)/0.1;  //calculate motor speed, unit is rpm
   encoder=0;
   //print out speed
   if (Serial.available() <= 0) {
     Serial.print("speed");
     Serial.println(pv_speed);         //Print speed (rpm) value to Visual Studio
     }
  //PID program
   if (motor_start){
     e_speed = set_speed - pv_speed;
     pwm_pulse = e_speed*kp + e_speed_sum*ki + (e_speed - e_speed_pre)*kd;
     e_speed_pre = e_speed;  //save last (previous) error
     e_speed_sum += e_speed; //sum of error
     if (e_speed_sum >4000) e_speed_sum = 4000;
     if (e_speed_sum <-4000) e_speed_sum = -4000;
   }
   else{
     e_speed = 0;
     e_speed_pre = 0;
     e_speed_sum = 0;
     pwm_pulse = 0;
   }
  //update new speed
   if (pwm_pulse <255 & pwm_pulse >0){
     analogWrite(pin_pwm,pwm_pulse);  //set motor speed 
   }
   else{
     if (pwm_pulse>255){
       analogWrite(pin_pwm,255);
     }
     else{
       analogWrite(pin_pwm,0);
     }
   }
}

At the beginning of program, it will receive commands from the computer (start/stop motor; motor speed settings; kP, kI, kD gain of PID). Next is void detect_a(): which is an encoder for sum calculation used for speed calculation in the Timer interrupt routine. Timer interrupt routine ISR(TIMER1_OVF_vect): every 0.1 this program is called; content includes: (1) Calculate motor speed (2) Send motor speed to the computer (3) Calculate PWM pulse (base on PID algorithm) (4) Push result of PWM to H-brigde. The entire of code for Arduino Pro mini can be downloaded at this link.

Step 3. Code on the computer

Visual Studio 2012 is used to make HMI programs, in which: (1) Send speed settings to Arduino    (2) Send PID gain (kP, kI, kD) to Arduino (3) Receive motor speed -> show on graph

The whole code for the Visual Studio program can be downloaded at this link. To make a Visual Studio program, see the detailed steps in this article. In general, the code will have:

#pragma endregion
 private: System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e) {
 serialPort1->Open();
 timer1->Start();
 mStr = "0";
 i=300;
 }
 private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
 serialPort1->WriteLine("vs_set_speed"+textBox1->Text); //send set_speed to Arduino
 serialPort1->WriteLine("vs_kp"+textBox2->Text); //send kP to Arduino
 serialPort1->WriteLine("vs_ki"+textBox3->Text); //send kI to Arduino
 serialPort1->WriteLine("vs_kd"+textBox4->Text); //send kD to Arduino
 }
 private: System::Void timer1_Tick(System::Object^  sender, System::EventArgs^  e) {
 String^ length;
 length=mStr->Length.ToString();
 if(mStr->Substring(0,5)=="speed"){
 speed=mStr->Substring(5,System::Convert::ToInt32(length)-6);
 label1->Text=speed;
 //print motor speed into Chart
 this->chart1->Series["Series1"]->Points->AddXY(i,System::Convert::ToDouble(speed));
 i++;
 this->chart1->ChartAreas["ChartArea1"]->AxisX->Minimum=i-300; //shift x-axis
 }
 }
 private: System::Void serialPort1_DataReceived(System::Object^  sender, System::IO::Ports::SerialDataReceivedEventArgs^  e) {
 mStr=serialPort1->ReadLine();
 }
 private: System::Void button2_Click(System::Object^  sender, System::EventArgs^  e) {
 serialPort1->WriteLine("vs_start"); //start motor
 }
 private: System::Void button3_Click(System::Object^  sender, System::EventArgs^  e) {
 serialPort1->WriteLine("vs_stop");  //stop motor
 }

Result