Understanding pulseIn

[gt7777]

I am trying to measure the frequency of rotation of a motor. I have a led and detector on either side of the motor. The motor has 3 arms so I get a signal 3 x the rotation. I have measured this waveform with a scope and its 20.89Hz BUT my code shows 22.95Hz. Multiplying this by 0.91 gives the the correct answer.

Any ideas why it won't read the correct frequency ?

Thanks

void setup()
{
pinMode(2,INPUT);digitalWrite(2, HIGH);
Serial.begin(115200);

}
void loop()
{
float freq = 0;
float ontime1 = 0;
float offtime1 = 0;
float ontime2 = 0;
float offtime2 = 0;
float ontime3 = 0;
float offtime3 = 0;
float period = 0;

ontime1 = pulseIn(2,HIGH);
ontime2 = pulseIn(2,HIGH);
ontime3 = pulseIn(2,HIGH);
offtime1 = pulseIn(2,LOW);
offtime2 = pulseIn(2,LOW);
offtime3 = pulseIn(2,LOW);
period = ontime1+offtime1+ontime2+offtime2+ontime3+offtime3;

freq = 1000000.0/period;
Serial.print (char(82));Serial.print (char(65));Serial.print (char(58));Serial.print (freq);Serial.print (char(10));

delay(100);
}

[UKHeliBob]

Please follow the advice on posting code given in posting code

In particular note the advice to Auto format code in the IDE and to use code tags when posting code here as it prevents some combinations of characters in code being interpreted as HTML commands such as italics, bold or a smiley character, all of which render the code useless

[slipstick]

pulseIn() returns an unsigned long not a float. But why not print the values you're getting to see where the error is coming from?

Steve

[anon73444976]

Serial.print (char(82));Serial.print (char(65));Serial.print (char(58));Serial.print (freq);Serial.print (char(10)); Is this for a code obfuscation contest?

   float freq     = 0;
   float ontime1  = 0;
   float offtime1 = 0;
   float ontime2  = 0;
   float offtime2 = 0;
   float ontime3  = 0;
   float offtime3 = 0;
   float period   = 0;
   
   ontime1  = pulseIn(2,HIGH);
   ontime2  = pulseIn(2,HIGH);
   ontime3  = pulseIn(2,HIGH);
   offtime1 = pulseIn(2,LOW);
   offtime2 = pulseIn(2,LOW);
   offtime3 = pulseIn(2,LOW);
   period   = ontime1+offtime1+ontime2+offtime2+ontime3+offtime3;

Or do you have to write a minimum number of LOCs?

Please remember to use code tags when posting code

[gt7777]

Thanks for the replies. I have changed to unsigned longs and printed the on and off times. They all add up to the reported frequency BUT I still believe it is incorrect.

Reported freq	ontime1	offtime1	ontime2	offtime2	ontime3	offtime3	sum	calc freq
23.14	6602	7730	6802	7559	6730	7795	43218	23.1385071035217
23.13	6802	7572	6722	7792	6601	7748	43237	23.1283391539654
23.13	6727	7790	6595	7747	6815	7563	43237	23.1283391539654
23.12	6598	7738	6822	7566	6738	7789	43251	23.1208526970475
23.14	6803	7566	6728	7780	6602	7731	43210	23.1427910205971
23.13	6735	7784	6592	7738	6820	7574	43243	23.1251300788567
23.12	6595	7729	6816	7575	6735	7801	43251	23.1208526970475

[gt7777]

I couldn't solve this but the following code gives the correct answer...

unsigned long time_start = 0;
unsigned long time_end = 0;
float freq;

void setup()
   {
   pinMode(2,INPUT);
   digitalWrite(2, HIGH);
   Serial.begin(115200); 
   }
void loop()
{
   while(digitalRead(2) == 0){ }
   while(digitalRead(2) == 1){ }
   time_start = micros();
   while(digitalRead(2) == 0){ }
   while(digitalRead(2) == 1){ }
   while(digitalRead(2) == 0){ }
   while(digitalRead(2) == 1){ }
   while(digitalRead(2) == 0){ }
   while(digitalRead(2) == 1){ }
   time_end = micros();
   freq = 1000000.0/((time_end - time_start));
   Serial.print (freq);
   Serial.print (char(10));
}