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Topic: Buzzer tone frequency and duration (Read 2300 times) previous topic - next topic

pablito0078

Hi,
I'm doing my very first arduino experiment (after blinking a led) with a buzzer and the CapacitiveSernsor library. Basically, as long as I touch an aluminium foil, the buzzer plays a tone and stops as I move my finger away.

The code I used is:

Code: [Select]
#include <CapacitiveSensor.h>

CapacitiveSensor csensor = CapacitiveSensor (4,2);
int buzzPin = 9; // use an analog Pin

void setup () {
 Serial.begin (9600);
 pinMode (buzzPin, OUTPUT);
}

void loop () {
 long start = millis();
 long sensor = csensor.capacitiveSensor (30);
 Serial.print  ("Reading");
 Serial.println (sensor);
 if (sensor > 100) {
   playTone ();
 }
 else {
   mute ();
 }

 delay (50);
}

void playTone () {
 analogWrite (buzzPin, 20);
}

void mute () {
 analogWrite (buzzPin, 0);
}


This works but the buzzer plays a 490Hz tone, according to the analogWrite() reference on the site. I'd like the buzzer play an higer tone so I found on the internet another snippet for my playTone() function that uses a digital pin instead of an analog one.

Code: [Select]
#include <CapacitiveSensor.h>

CapacitiveSensor csensor = CapacitiveSensor (4,2);
int buzzPin = 7;

void setup () {
 Serial.begin (9600);
 pinMode (buzzPin, OUTPUT);
}

void loop () {
 long start = millis();
 long sensor = csensor.capacitiveSensor (30);
 Serial.print  ("Reading");
 Serial.println (sensor);
 if (sensor > 100) {
   playTone ();
 }
 else {
   mute ();
 }

 delay (50);
}

void playTone () {
 for (long i = 0; i < 2048; i++ )
   // 1 / 2048Hz = 488uS, or 244uS high and 244uS low to create 50% duty cycle
 {
   digitalWrite(buzzPin, HIGH);
   delayMicroseconds(244);
   digitalWrite(buzzPin, LOW);
   delayMicroseconds(244);
 }
}

void mute () {
 digitalWrite (buzzPin, LOW);
}



In this case the buzzer plays only a 1 second tone so it does not play as long as I touch the aluminium foil sensor. What I miss is the logic behind the loop. My understanding is that it sends 2048 HIGH / LOW messages to the buzzer to create a 2048Hz tone. But what the delayMicrosecond() functions are used for? and how to change the code to achieve my goal?

Thank you very much!

P.S. I use an Arduino Duemilanove and not an Uno.

AWOL

#1
Nov 04, 2012, 06:53 pm Last Edit: Nov 04, 2012, 06:55 pm by AWOL Reason: 1
Quote
But what the delayMicrosecond() functions are used for?

To produce the required frequency.
I'd say the frequency is probably a little off (too low) - the delays don't account for the relatively long time the  digitalWrites take.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dc42

Have you looked at the Tone library?
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

pablito0078

Thanks. I will check the Tone library.

PeterH


My understanding is that it sends 2048 HIGH / LOW messages to the buzzer to create a 2048Hz tone. But what the delayMicrosecond() functions are used for?


I'm not sure, but I suspect you have misunderstood what playTone() is doing. In your explanation, the two numbers '2048' do not represent the same thing.

2048 is the number of pulses that are output. The delay interval determines approximately how long each pulse is i.e. it determines the frequency. The tone will continue until the specified number of pulses have been output. If the delay is short, that would be a high pitched and very short note. If the delay is long, that would be a low pitched and longer note.

The problem with this approach is that it produces a single burst of sound of fixed length each time it finds the switch activated, rather than producing a continuous sound which starts and stops promptly as the input changes. Based on the description of what you're trying to achieve, I suspect you would be better either using a timer to generate the sound (and perhaps the tone library would help here) or using the techniques illustrated in the 'blink without delay' example to toggle the output high and low to produce the output wave. (I don't know how fast it would be possible to go with that design - it may not be feasible to produce the frequency you're asking for).
I only provide help via the forum - please do not contact me for private consultancy.

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