I am trying to make a IR sensor but somehow its not working.Below is my circuit diagram

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when i bring my hand near the sensor, the led connected to pin1 of lm358N does not glow. I also checked the voltage at pin2 of LM358N ,it is reading 5v whereas pin3 reads 3.2 v. when i bring my hand near the IR sensor, the voltage remains same.

I actually tested my circuit using tv remote and found that my IR recevier is working fine so may be transmitter have the problem .so i took my cell phone any saw the transmitter using my cell phone camera but couldn't see anything .I have changed my transmitter but still i cant see radiation in my camera .whereas my tv remote transmitter radiation was visible.what could be the problem?

  • \$\begingroup\$ Are you using an all-in-one sensor with both the transmitter (A) & receiver (B) in one package, or 2 separate components? \$\endgroup\$ – brhans Mar 26 '15 at 13:09
  • \$\begingroup\$ i am using 2 separate components \$\endgroup\$ – dcmotor Mar 26 '15 at 13:10
  • \$\begingroup\$ What happens to the voltage at pin 2 if you point A directly at B? \$\endgroup\$ – brhans Mar 26 '15 at 13:10
  • \$\begingroup\$ pin2 voltag reading is 5v \$\endgroup\$ – dcmotor Mar 26 '15 at 13:14
  • \$\begingroup\$ Then either A or B is broken or you've made a wiring error ... \$\endgroup\$ – brhans Mar 26 '15 at 13:17

Measuring 5V at pin 2 indicates that the IR receiver is not conducting any current, which would suggest that: a) it is not connected (try re-wiring that portion of the breadboard), b) it is not being illuminated with enough IR to conduct (maybe the IR transmitter is backwards--try reversing it), or c) it is broken (try another receiver).

Digital cameras, including ones on cell phones are sensitive to IR. Try using a digital camera to see if the IR transmitter is working. You might have to point the IR LED directly at the camera and possibly turn off the lights in the room. You can test it with a TV remote control that you know works.

  • R1 1K is too much. I'd go with 330ohm or 270ohm to drive the IR led at full 20mA current.
  • watch out of the polarity of the IR leds. I have had surprises with certain types, anode and cathode were marked differently.
  • if you can not see the IR led transmission with a camera (while you can see other IR transmitters with your camera) then the IR trasmitter is not working :)

Note that the normal IR transmitters use a high frequency modulation on the IR led, allowing it to drive with peak currents of over 1A to get a better range. Since the led is modulated, it has enough time to cool down, this way the 1A peaks will not make the led burn out. The modulation also helps to separate IR communication from steadly lights, such as direct sunlight - which would be detected as a valid infrared signal by your direct receiver. (Note that sunlight contains a lot of infrared, as well as many incadescent light sources.)

Instead of a comparator, you may wish to use an inexpensive off the shelf modulated IR receiver, such as http://www.vishay.com/docs/82491/tsop382.pdf which contains an AGC and offers you exceptional transmission range. The transmission side needs the led being flashing at 38kHz - you can do that with a microcontroller, or a simple 555 chip.


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