//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);
}
My magnet for my sensor is set up on a rotating part while my actual hall effect sensor is mounted onto the frame. I am able to calculate the speed at which the magnet (and therefore the rotating part) is moving and what I want to find out is what is the total distance that the magnet has traveled. I understand that when one revolution has been completed that the magnet will have traveled a total distance that is equivalent to the circumference of the rotating part, but I want to program the arduino to calculate exactly how far the magnet has traveled and then display this information onto an LCD display as is already the case with the speed measurement. I'm creating this sensor to mount onto a bicycle and hopefully with this setup I will be able to visually see the speed that I am traveling at and the total distance that I have traveled over a trip. I hope that this clears up any confusion.