OH137 Hall Effect Switch

[Lesthegringo]

Hi All

I have used OH137 hall effect switches successfully in the past using Leo Bodnar boards, making things like non-contact 'gearboxes' for Race sims

I want to know how to use them with Arduinos. I have no specific project in mind, this is simply trying to learn. I have connected one OH137 and an LED in the following way

and have looked on the web for some code and found this

int hallSensorPin = 6;     
int ledPin =  2;    
int state = 0;          
void setup() {
  pinMode(ledPin, OUTPUT);      
  pinMode(hallSensorPin, INPUT);     
}
void loop(){
  
  state = digitalRead(hallSensorPin);
  if (state == LOW) {        
    digitalWrite(ledPin, HIGH);  
  } 
  else {
    digitalWrite(ledPin, LOW); 
  }

  
Serial.begin(9600);
Serial.println(state);
}

The LED is working fine, but clearly something is up with either the sketch, circuit or both! Even using neodymium magnets I can't get any response from the hall effect sensor

Can anyone advise of how to get the sensor to work with an Arduino?

Cheers

Les

[PaulRB]

pinMode(hallSensorPin, INPUT_PULLUP);

[PaulRB]

@Lesthegringo

Serial.begin(9600);

Why is this in loop(), Les? Think: when have you ever seen this function in loop()?

[Lesthegringo]

Thanks, that resolved it

As for the Serial.begin (9600), as you point out never - I have put it in it's rightful location

Cheers

Les

[PaulRB]

Great, but do you understand why INPUT_PULLUP was needed?

[Lesthegringo]

As I understand it it it forces the default state to be high or low to make the input easier for the Arduino to read

[TomGeorge]

It is because the sensor has an open collector output.

You need to provide a path for the collector current to flow to get a HIGH or LOW voltage response from the sensor.

In fact if you still have some switching instability you could add a 10K or lower pullup resistor.

Tom..

[Lesthegringo]

Thanks, nice explanation!

I tested out the sketch with the hardware yesterday, and it was totally stable, so it looks like the resistors aren't essential, however I may try it again today with the resistor to see if there is any difference. Would the resistor also potentially improve reliability?

Les