Hi all,
I’m new in this forum… I bought an Arduino UNO and 6 HC SR04 sensors a few days ago.
I’ve googled a bit and I found the NewPing library
http://code.google.com/p/arduino-new-ping/
which lets you manage the sensors’ ping. 
I’ve used the example shown here
http://playground.arduino.cc/Code/NewPing
and I think it is great if you’re playing with the Arduino, but I want something more from this great board, than it.
I’d like to build a Event-driven system using the Timer1 which is into UNO’s chip.
I’ve thought to use the internal timer to manage the Task which get the data from the sensors using the Job “read_distance”.
So every period X, the timer is pinging the sensors one-by-one to get the different distances from them.
I’ve written some lines of code and if I use only one sensor the program works perfectly, but when I increase the number of sensors it doesn’t work anymore.
Here you are my code:
#define trigPin 2 // Trigger Pin
#define echoPin1 5 // Echo Pin for sensor # 1
#define echoPin2 6 // Echo Pin for sensor # 2
#define echoPin3 7 // Echo Pin for sensor # 3
#define echoPin4 8 // Echo Pin for sensor # 4
#define echoPin5 9 // Echo Pin for sensor # 5
#define echoPin6 10 // Echo Pin for sensor # 6
#define SENSORS_NUMBER 6
#define MAXIMUM_RANGE 200 // Maximum range needed
#define MINIMUM_RANGE 0 // Minimum range needed
volatile boolean time_elapsed;
volatile byte i;
volatile byte vect[] = {-2, -2, -2, -2, -2, -2};
void read_distance(byte sensor_trig_pin, byte sensor_echo_pin, byte sensor_id);
void setup()
{
pinMode(trigPin, OUTPUT);
pinMode(echoPin1, INPUT);
pinMode(echoPin2, INPUT);
pinMode(echoPin3, INPUT);
pinMode(echoPin4, INPUT);
pinMode(echoPin5, INPUT);
pinMode(echoPin6, INPUT);
// open the serial port at 9600 bps:
Serial.begin(9600);
// initialize Timer1
cli(); // disable global interrupts
TCCR1A = 0; // set entire TCCR1A register to 0
TCCR1B = 0; // set entire TCCR1B register to 0
// set compare match register to desired timer count, corresponds to 1 second
OCR1A = 15624; // Timer 1 Output Compare Register A
// turn on CTC mode on Timer1:
TCCR1B |= (1 << WGM12);
// Set CS10 and CS12 bits for 1024 prescaler:
TCCR1B |= (1 << CS10);
TCCR1B |= (1 << CS12);
// enable timer compare interrupt:
TIMSK1 |= (1 << OCIE1A);
// enable Timer1 overflow interrupt:
//TIMSK1 = (1 << TOIE1);
// enable global interrupts:
sei();
time_elapsed = false;
}
ISR(TIMER1_COMPA_vect)
{
read_distance(trigPin, echoPin1, 0);
read_distance(trigPin, echoPin2, 1);
read_distance(trigPin, echoPin3, 2);
read_distance(trigPin, echoPin4, 3);
read_distance(trigPin, echoPin5, 4);
read_distance(trigPin, echoPin6, 5);
time_elapsed = true;
}
void loop()
{
if(time_elapsed){
for(i = 0; i < SENSORS_NUMBER; i++){
Serial.print(" # ");
Serial.print(i+1);
Serial.print(" :");
Serial.println(vect[i]);
}
time_elapsed = false;
}
}
void read_distance(byte sensor_trig_pin, byte sensor_echo_pin, byte sensor_id){
long duration; // Duration used to calculate distance
long distance;
digitalWrite(sensor_trig_pin, LOW);
delayMicroseconds(2);
digitalWrite(sensor_trig_pin, HIGH);
delayMicroseconds(10);
digitalWrite(sensor_trig_pin, LOW);
duration = pulseIn(sensor_echo_pin, HIGH);
//Calculate the distance (in cm) based on the speed of sound.
distance = duration/58.2;
if (!(distance >= MAXIMUM_RANGE || distance <= MINIMUM_RANGE)){
vect[sensor_id] = distance;
}
else{
vect[sensor_id] = -1;
}
}
I’ve configured Timer1 with CTC mode and I’ve set the prescale to 1024 (# Divisions).
The OCR1A value has been evaluated according to the following formula:
The value of OCR1A corresponds to 1 second; so every time Timer1 reaches that value, 1 second has gone, ISR function is executed, and inside of it there are 6 calls to the function which get distances using the sensors.
All the sensors uses the same trigPin, the only pin which changes is the echoPin.
I can’t understand where is the problem, maybe the timer but I’m not shure.
Can you help me please?
You can see my elcetrical scheme here attached to the topic.
