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Topic: REVERSE VALUES IN ELECTRET MICROPHONE (Read 6038 times) previous topic - next topic


So you need to put a 10K resistor between the BASE of the TIP122 and the output pin of the arduino.

Please tell me if you understand this and have done it, also checked the pin outs of the TIP122.

Also for the response you need you need to connect the motor wire to the Normally Open terminal of the relay and the motor supply  wire to the Common terminal of the relay.

Did you look at the link I put in my previous Post?

Tom..  :)

Yes thanks Tom I figured out how the pins work and I put a resistor before plugging it in the arduino. However, the values I get are still pretty random.

That is quite simply impossible unless you have screwed up with your code. That is why we ask you to post the code you are using not a link to the code you think you are using.
Normally the reading you will get with silence is around 512, so setting a threshold at this point is useless.
It sounds like you are using the raw output of your sound sensor not the correct one.

First code I used was the one from Arduino Cookbook. Without using a transistor between output and arduino the values I get from the MIC output are between 3,000 and 6,000 in silence and over 10,000 in noise. From the SPL output 50,000 to 85,000 in silence and they get low as 9,000 in noise. Using a 10K resistor between arduino analog and SPL output I get 50,000 and 100,000 in silence and they get as low as 6000 when there is noise. If I connect to the mic output it is between 3,000 to 6,000 in silence and over 10,000 when there's noise again. This is the code without tinkering anything.The light remains on the whole time.

Code: [Select]
microphone sketch

SparkFun breakout board for Electret Microphone is connected to analog pin 0

const int ledPin = 13;            //the code will flash the LED in pin 13
const int middleValue = 512;      //the middle of the range of analog values
const int numberOfSamples = 128;  //how many readings will be taken each time

int sample;                       //the value read from microphone each time
long signal;                      //the reading once you have removed DC offset
long averageReading;              //the average of that loop of readings

long runningAverage=0;          //the running average of calculated values
const int averagedOver= 16;     //how quickly new values affect running average
                                //bigger numbers mean slower

const int threshold=400;        //at what level the light turns on

void setup() {
  pinMode(ledPin, OUTPUT);

void loop() {
  long sumOfSquares = 0;
  for (int i=0; i<numberOfSamples; i++) { //take many readings and average them
    sample = analogRead(0);               //take a reading
    signal = (sample - middleValue);      //work out its offset from the center
    signal *= signal;                     //square it to make all values positive
    sumOfSquares += signal;               //add to the total
  averageReading = sumOfSquares/numberOfSamples;     //calculate running average

  if (runningAverage>threshold){         //is average more than the threshold ?
    digitalWrite(ledPin, HIGH);          //if it is turn on the LED
    digitalWrite(ledPin, LOW);           //if it isn't turn the LED off
  Serial.println(runningAverage);        //print the value so you can check it

If now using the mic output without the resistor I change the mid value to 5,000 and 6,000 for the threshold I get results below zero (-133,333,569) and the light does not flash. If I change to the SPL output put 50,000 for mid value and 60,000 for threshold and reverse LOW and HIGH I do get the light to turn on with the sound of my voice although it randomly blinks the whole time afterwards even in silence.

I do have the same issue when I use the code I posted in the first place. I can make the relay turn ON/OFF my issue was that the normal state should be either on or off but the microphone's values were turning the relay on/off continuously and they kept on for longer when there was noise.


Problem seems to be solved somehow. I changed my relay with a solid state one,used a BD139 transistor and also I plugged in the microphone VCC into the 3.3 V instead of the 5V. Probably the problem is still there but the voltage is now too low to make the lights blink uncontrollably. It seems that the microphone was getting too much voltage from the arduino although when it was independent from it even with a 6 V battery it was working perfectly.

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