View Full Version : Help using IR circuit

02-06-2005, 12:36 AM
Hi friends,
I got an IR detector and IR led from a electronic shop. Both looked like a LED exactly identical. How can i make out which one is the sensor and which one is the emitter. Also do any one of u have any circuits using those components. I am planning to build a Line following robot so i need a IR sensing circuit where can i find one. kindly help me. Thank u,

With warm Regds,

02-06-2005, 12:59 AM
When I got mine, the detector had a dark colour and emitter was transparent.

Here's a simple line follower




02-06-2005, 06:44 AM
mine was sometimes the opposite...
u can try this method..
Take one f the diodes,connect it to your multimeter and keep the meter on max ohms
Take the diode to a high "light" area..like sunlight...if the resistance on the meter drops,thats your detector...if it doesnt thats your emitter

02-06-2005, 03:44 PM
hi pal best way out to see which is a sensor &which is a led foward bias both the diode at about 3V and bring them opposite to a web cam or a digital cam u will get ur answer.

02-06-2005, 05:05 PM
Hey guys,
Thanks a lot for the suggestions. I will try this one out.
With Warm Regds,

02-08-2005, 12:30 AM
Hey ice,
You are really cool. Ur idea to find IR detector worked well. Thanks a lot for that.
As i said early that i am working on a line following robot (LFbot). First for a start i got the LM324N IC along with the resistors and pot. I connected the IR led and the detector only a single one for testing. When i switch on the circuit the ordinary led connected to pin 1 of the IC was glowing. I changed the value in the pot. At some particular value the led switched off. when i closed the detector nothing happened. No reaction on the circuit even when i pulled the IR detector or the led from the circuit. what should be the problem. Is there something like i should connect the whole circuit then only it will work. Or what else can i try with the IR detector so that make sure that a simple IR detector circuit is working. I am fed up with this. Kindly help me. If u could chat with me here itself it would be great. One more problem. What should we do for giviing input for a PIC. Can we connect the positive voltage directly to the ip pin after setting it as input in the program.

With warm Regds,

02-08-2005, 06:29 AM
ur welcome.
Actually the webcam idea by asimov_1 is also one of the easiest.i usually use my webcam to debug diodes if they are working when soldered to the circuit.

i assume this is ur circuit setup which happy_99 mentioned ,with one of the 324's comparator being used

Check this:
1> THE basic theory of the circuit>>the output of the 324 is inverted because the detector is connected to the inverting pin of the 324.when theres no ir falling on the detector..the inverting pin gets a high ,giving a low on the output(provided voltage at pin 2 is higher than pin 3 set by the pot).
This allows the LED to glow ,because the comparator sinks current.

When light does fall on the detector,the volage at pin 2 falls .If it falls below the voltage at pin 3 ,the output goes high.This causes the LED to shut off.

2>try this out,
a)set the pot to one end so tht the LED glows
b)as u vary the pot,short the receiving diode.The point where the LED shuts off shows tht ur ckt works..

You may have to read this twice or thrice to understnd whts written..but u'll get it eventually


02-09-2005, 01:05 AM
Hi Ice,
I understood what u said. When i tried to short the IR detector the IC is getting heated. So i stopped it. Later after thinking for a while i connected a 15K resitor in parallel to the IR detector. Thats it, the circuit is working well. I was very happy to see the circuit working. Thanks a lot for ur help.

With warm Regds,

03-15-2005, 10:51 PM
hi pal best way out to see which is a sensor &which is a led foward bias both the diode at about 3V and bring them opposite to a web cam or a digital cam u will get ur answer.

Hi there,

I am a newbie into this forum, but I am curious to know how to use a web cam or digicam to find out which is sensor and which is emitter?

Being from Bangalore, India originally; presently I am in the UK and here I use a SHARP IR Ranger which is easily available for this purpose - but I am curious to know how to use a webcam/digicam to find which is sensor etc?

Thanks in advance

03-28-2005, 07:31 PM
we bought an IR LED pair(emitter and detector) and carried out the same tests all of u guyz mentioned...i.e..digi cam for emitter...multimeter test for detector...and we concluded that one was an emitter and the other detector...but...in the circuit of Line following robot..if we replace 10k resistance with 270 ..even the detector is starting to glow..can a detector(??) work as a emitter when the resistor connected is of lowresistance and as a detector ??...i need to mention that both of them are looking like LEDs only...one (emitter) was of transparent olive color and the other (detector) was of transparent violet color on which i conducted both tests ...but on the first one i conducted only digi cam test..
or shud we buy a detector given in this link..its costly..
i seriously need some help...i am constructing the same line following robot but i am struck at this point with the electronics shop guy giving some arbit stuff instead of the ones i need... :-(

03-29-2005, 10:24 AM
even the detector is starting to glow..
..never experienced anything like this..and no it shouldn't glow.Detectors don't glow.Try another piece.Also remember when buying IR emitters/detectors,buy around 5 to 6 pairs...allows for testing.

The link which you mentioned uses the TSOP1738 infrared detector..note that this sensor receives /detects only around 38 to 40Khz frequencies ,which means you need to generate such a frequency[using a 555 or a micro]..it costs aroun 30 to 40 bucks

03-30-2005, 12:33 AM
yaa...ur info was useful..and finally no one was giving us IR detectors..so we removed IR pair from a ball mouse and wow...its working...ofcourse...junta r discarding ball mouses...and..i need a small info..i.e..data sheets or somestuff...coz..there were no numbers on that small IR pair...and i dont know this...the IR detector has 3 terminals..and i want to know which terminal shud be connected to wat..any help wud be gratefull... :-)