IR receiver continuous signal

Hello!

I am new to this forum and I have signed in since I didn't find a satisfying answer to my problem.

In my project all I need to do is check if something is blocking the path between an emitter and receiver. They are about 1 or 2 meters apart. I used an IR LED and IR receiver TSOP34836. The problem is that the signal needs to be modulated, so the receiver filters out the continuous signal at 36kHz. This is fine if using a IRremote control, but for my project it is not since I want a continuous signal to constantly check if the path is blocked or not.

I found that TSOP58038 and TSOP4038 can use a continuous signal at 36kHz. But before I order them I would like to know if you guys maybe have a better or easier solution to this problem. Remember that they are at least 1meter apart, better 2meters.

Thank you in advance!

You could modulate the current in the LED at 36khz using an a stable oscillator or Arduino output pin.

Weedpharma

Yes, of course, I have done that and I checked that I am sending out 36kHz ir signal. But I still have problems. My signal is quite strong and even if I cover the receiver it still detects something and of course I don’t want that ( I suppose the reflection plays a role here…). I used this code :

for(int i=0;i<70;i++){ // pulsing signal at 36kHz
digitalWrite(pin, HIGH);
delayMicroseconds(1); //duty cycle is therefore lower than 50% because I want to make my signal weaker
digitalWrite(pin, LOW);
delayMicroseconds(13);
}
for(int i=0;i<100;i++){ //pause between the 36kHz signal
digitalWrite(pin, LOW);
delayMicroseconds(7);
digitalWrite(pin, LOW);
delayMicroseconds(7);
}

What if I use a basic raw black LED IR receiver (without the integrated demodulator etc…) and use a continuous DC signal at emitter? I know that can work but how apart can they be to still work, any experience on that?

even if I cover the receiver it still detects something

This does not make sense. If you are still getting a signal, you are not covering the sensor. Cover the Tx and check again.

Without modulation, you will pick up IR from anywhere.

Weedpharma

The last two digits of those 3-pin receivers is the frequency. Range is very small if you send a 38kHz signal to a 36kHz receiver.

This sketch generates a continuous 36kHz transmitter signal in void setup() Receiver code (if used) is in void loop() Leo..

const byte IR_LED = 11; // IR transmitter LED with 100ohm (minimum) CL resistor
const byte IR_Receiver = 8; // from receiver output
const byte onboard_LED = 13; // onboard indicator LED
boolean receiverState;

void setup() {
  pinMode (onboard_LED, OUTPUT);
  pinMode (IR_LED, OUTPUT);
  pinMode (IR_Receiver, INPUT);
  // from Nick Gammon
  TCCR2A = _BV (COM2A0) | _BV(WGM21);
  TCCR2B = _BV (CS20);
  OCR2A =  219; // ~209 = ~38kHz | ~219 = ~36kHz
}

void loop() {
  receiverState = digitalRead (IR_Receiver);
  if (receiverState == HIGH) { // beam interrupted
    digitalWrite(onboard_LED, LOW); // green onboard LED off
    delay(1000);
  }
  else { // beam detected
    digitalWrite(onboard_LED, HIGH); // green LED on
  }
}

I think people are looking at apples and oranges. It sounds like the 36khz carrier is being generated, however some sensors require additional modulation of the carrier to generate an output while there are other sensors out there that will give an output as long as the 36khz carrier is present (I got bitten by this one a while back and ended up modulating the 38khz carrier with a 1khz square wave which then was able to be detected by the receiver. I think this is the modulation that is being discussed not the 36 or 38khz carrier. For example, the TS?P4038 comes in several different configurations where the "?" is - according to the

Data Sheet

O = for IR receiver applications M = for repeater/learning applications S = for sensor applications

Yes, knew about that, but I didn’t dig too deep into the datasheets. Thanks for adding that.
I think receivers that need an interrupted carrier are not really suitable for a beam break sensor.
I always use the PNA4602M and SFH400.
This gives me 5+ meters in daylight with only ~25mA peak LED current. And a <=1msec reaction time.
Leo…

Wawa:
Yes, knew about that, but I didn’t dig too deep into the datasheets. Thanks for adding that.
I think receivers that need an interrupted carrier are not really suitable for a beam break sensor.
I always use the PNA4602M and SFH400.
This gives me 5+ meters in daylight with only ~25mA peak LED current. And a <=1msec reaction time.
Leo…

In general, you are correct. I was not aware of the modulated carrier either until it didn’t work with a plain carrier and I went back and looked at the data sheets for a while (different part, but same issue). I was looking to grab some pictures of whomever was climbing over the fence and doing things in the back yard. Their dad was NOT happy when I handed him the pictures (I used it to trigger a 35mm camera). heh heh :slight_smile:

Nothing that exciting here. Just sports timers.
Picture of a Curling Timer project for practising sliding speed of the stones.
Gate width up to 5 meters, and distance between two gates (start/stop) ~20 meters.
Leo…
Curling.png

Curling stones - like a bowling ball except flat on two sides :)