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# Self-balancing Car Kit For Arduino Robot Project 5: Internal Timer Interrupt

Posted by Fiona Su on

Description:
In previous section, you have learned how to get the number of pulses by Hall encoder of motor within 100ms.
Now, we will use the built-in internal timer (timer2) of REV4 board. Calculate out the specified speed by the number of pulses got from Hall encoder within 100ms.

Source Code:
Before test the source code, do remember to add the corresponding library.
You can refer to the method in the link below:
https://wiki.keyestudio.com/How_to_Install_Arduino_Library

```#include <MsTimer2.h>

//TB6612 pins
const int right_R1=8;
const int right_R2=12;
const int PWM_R=10;
const int left_L1=7;
const int left_L2=6;
const int PWM_L=9;

const int PinA_left = 5;        //set the left motor’s pulse pin to D5
const int PinA_right = 4;       //set the right motor’s pulse pin to D4

int times=0,newtime=0,d_time=100;   // time, new time, time interval
int valA=0,valB=0,flagA=0,flagB=0;   //variable valA and valB for calculating the number of pulse

void setup()
{
Serial.begin(9600);

pinMode(right_R1,OUTPUT);     //set the TB6612 pins to OUTPUT
pinMode(right_R2,OUTPUT);
pinMode(PWM_R,OUTPUT);
pinMode(left_L1,OUTPUT);
pinMode(left_L2,OUTPUT);
pinMode(PWM_L,OUTPUT);

pinMode(PinA_left,INPUT);      // set the pulse pin to INPUT
pinMode(PinA_right,INPUT);

MsTimer2::set(100, inter); // trigger an interrupt per 100ms
MsTimer2::start();    // start interrupt
}

void loop()
{
//both motors turn forward
digitalWrite(right_R1,HIGH);
digitalWrite(right_R2,LOW);
digitalWrite(left_L1,HIGH);
digitalWrite(left_L2,LOW);
analogWrite(PWM_R,100);    //write into PWM value 0~255（speed）
analogWrite(PWM_L,200);

if(digitalRead(PinA_left)==HIGH&&flagA==0)     // calculate the pulse value
{
valA++;
flagA=1;
}
{
valA++;
flagA=0;
}

{
valB++;
flagB=1;
}
{
valB++;
flagB=0;
}

}

//interrupt function
void inter()
{
sei();    //allow whole interrupts
Serial.print("valA = ");     //print out the pulse value on serial monitor
Serial.println(valA);
Serial.print("valB = ");
Serial.println(valB);
valA = valB = 0;
}
```

Test Result
Installed well the balance car, power on and upload the source code to the board;
Turn the slide switch ON.
Then open the monitor of Arduino IDE, set the baud rate to 9600.
The serial monitor will pop up the number of pulse got from Hall encoder within 100ms ( correspond to left and right motor).
See the figure below.

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