Hall Effect Speed and Distance Sensor Code

Projects Programming
4 
//outputs speed of bicycle to LCD 

//calculations 
//tire radius ~ 13.5 inches 
//circumference = pi*2*r =~85 inches 
//max speed of 35mph =~ 616inches/second 
//max rps =~7.25 

#define reed A0//pin connected to read switch 

//storage variables 
float radius = 13.5;// tire radius (in inches)- CHANGE THIS FOR YOUR OWN BIKE 

int reedVal; 
long timer = 0;// time between one full rotation (in ms) 
float mph = 0.00; 
float circumference; 
boolean backlight; 

int maxReedCounter = 100;//min time (in ms) of one rotation (for debouncing) 
int reedCounter; 


void setup(){ 

 reedCounter = maxReedCounter; 
 circumference = 2*3.14*radius; 
 pinMode(1,OUTPUT);//tx 
 pinMode(2,OUTPUT);//backlight switch 
 pinMode(reed, INPUT); 

 // TIMER SETUP- the timer interrupt allows preceise timed measurements of the reed switch 
 //for mor info about configuration of arduino timers see http://arduino.cc/playground/Code/Timer1 
 cli();//stop interrupts 

 //set timer1 interrupt at 1kHz 
 TCCR1A = 0;// set entire TCCR1A register to 0 
 TCCR1B = 0;// same for TCCR1B 
 TCNT1 = 0; 
 // set timer count for 1khz increments 
 OCR1A = 1999;// = (1/1000) / ((1/(16*10^6))* 8 ) - 1
 // turn on CTC mode 
 TCCR1B |= (1 << WGM12); 
 // Set CS11 bit for 8 prescaler 
 TCCR1B |= (1 << CS11); 
 // enable timer compare interrupt 
 TIMSK1 |= (1 << OCIE1A); 

 sei();//allow interrupts 
 //END TIMER SETUP 

 Serial.begin(9600); 
} 

ISR(TIMER1_COMPA_vect) {//Interrupt at freq of 1kHz to measure reed switch 
 reedVal = digitalRead(reed);//get val of A0 
 if (reedVal){//if reed switch is closed 
 if (reedCounter == 0){//min time between pulses has passed 
 mph = (56.8*float(circumference))/float(timer);//calculate miles per hour 
 timer = 0;//reset timer 
 reedCounter = maxReedCounter;//reset reedCounter 
 } 
 else{ 
 if (reedCounter > 0){//don't let reedCounter go negative 
 reedCounter -= 1;//decrement reedCounter 
 } 
 } 
 } 
 else{//if reed switch is open 
 if (reedCounter > 0){//don't let reedCounter go negative 
 reedCounter -= 1;//decrement reedCounter 
 } 
 } 
 if (timer > 2000){ 
 mph = 0;//if no new pulses from reed switch- tire is still, set mph to 0 
 } 
 else{ 
 timer += 1;//increment timer 
 } 
} 

void displayMPH(){ 
 Serial.print("Speed = "); 
 Serial.print(mph); 
 Serial.println(" MPH "); 
} 

void loop(){ 
 //print mph once a second 
 displayMPH(); 
 delay(1000); 
}

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