phototransistor and motor with time reset

Development Boards Arduino
1

As the subject states i want to use a phototransistor to start a motor and when the motor starts it’s supposed to stay on for 7 seconds. And if the phototransistor is affected during the 7 seconds it should ignore that. the whole project is basically when the phototransistor reaches a certain value in my room the motor is suppose to go on for 7 seconds and then shut itself of. Hope you understand what i mean. Would be happy if anyone can point me in the right direction.

the code below is what i got so far

int sensePin =0;
int motorPin = 12;

void setup (){
 analogReference(DEFAULT); 
 
 pinMode(motorPin, OUTPUT);
 
}

void loop () {
  int val = analogRead(sensePin);
  
  if(val < 100) digitalWrite(motorPin,LOW);

  else digitalWrite(motorPin, HIGH);
}
2

If you really are doing nothing more than turning on the motor and then turning it off after 7 secs, why not ;

- read the analog voltage
- decide if it's over the threshold (I would add    and over for long enough)
- if over threshold
      * turn on the motor
      * delay 7 secs (  delay(7000); )
      * turn the motor off
- go back to top of loop

There are other ways but the above is the simplest and good enough if that’s all you’re doing.

http://arduino.cc/en/Reference/Delay

3

The problem is if i use delay it will turn it of for only 7 seconds and then turn the motor back on. Its only supposed to start one time once the value on the phototransistor has been reached.

4

OK so it’s a one time only deal … presumably until the Arduino is reset or power removed ?

Use a variable, motorRun, and initialize it to 0. When the motor runs, set it = 1. The motor has run. Now add an additional statement as in :

- if over the threshold and if motorRun = 0
   * then run the motor for 7 secs
   * motorRun = 1
   * etc, etc

That way the motor will run only when it hasn’t run before.

5

“presumably until the Arduino is reset or power removed ?” Yes

I still don’t get it.

I made changed my code now and this is the result.

int sensePin =0;
int motorPin = 12;

void setup (){
 analogReference(DEFAULT); 
 
 pinMode(motorPin, OUTPUT);
 
}

void loop () {
  int val = analogRead(sensePin);
  
  if(val < 100) digitalWrite(motorPin,LOW);

  else digitalWrite(motorPin, HIGH);
  
  int motorRun = digitalRead(motorPin);
  if(motorRun == HIGH) digitalWrite(motorPin,LOW);
  else delay(7000); digitalWrite(motorPin,HIGH);
}

So now when i hold my hand over the phototransistor it starts the motor for 7 seconds before turning of. But if i keep my hand over the phototransistor it wont turn of after 7 seconds. I tried doing what you wrote but my arduino programming skills aint that good yet :slight_smile:

6

I"ll assume 100 is your threshold and a HIGH turns the motor on. If that’s backwards, well you can figure it out from here.

//declare the constants 
const int sensePin = 0;
const int motorPin = 12;

//declare the global variables
int motorRun = 0;
int val = 0;

void setup () {
  Serial.begin(9600);                 //initialize serial port to 9600 baud
  analogReference(DEFAULT);           //not really need but OK
  pinMode(motorPin, OUTPUT);          //set pin to output
  digitalWrite(motorPin,LOW);         //make sure motor is off
}

void loop () {
  val = analogRead(sensePin);
  Serial.print("Sensor reads ");
  Serial.println(val);
  if( (val >= 100) && (motorRun == 0) ) {
    //both above threshold and motor has not run yet
    Serial.println("Turning motor on");
    digitalWrite(motorPin, HIGH);           //turn motor on
    motorRun = 1;                           //memorize that motor has run
    delay(7000);                            //wait 7 secs
    Serial.println("Turning motor off");  
    digitalWrite(motorPin,LOW);             //turn motor off
  }
}

The above will turn on the motor for 7 secs on the VERY FIRST instance of val >= the threshold. Noise may trigger the motor.

http://arduino.cc/en/Reference/Boolean

ps - what do you have for a motor and how do you have it driven ?

7

Can’t you use delay?

8

Got some random DC motor(9v) which is connected to my relay.

When i use your code and I check the serial Monitor it says starting motor and it randomly starts and stops. i tried changing the value of the " if( (val <= 100) && (motorRun == 0) " to 300 but did not make any difference.

9

What do the printout say ? Is the reading from the sensor flucuating ? Does the motor turn off after 7 secs ? Do you see only 1 message to turn the motor on … and off ? Where’s the power for the motor coming from ? Hopefully not from the Arduino. What’s the coil for the relay rated at ? How much current does it draw ? Do you have a suppression diode in place ?

IOW are you seeing a software problem or a hardware problem ?

10

I think i got it working now. I changed all the HIGH values to LOW and the LOW to HIGH. I think somehow i inverted it when i hooked things up. Big thanks to you Mee_n_Mac. :smiley: