proximity sensor : low range

[ikalogic]

hi everybody,
i build this ir based proximity sensor...
all the components are on the same plane, so the IR receiver will only receive IR that is reflected on an object in front or the board..

But the results are not exactly what i expect, the range is really low: only 4 to 5 cm in best conditions!!!
it is strange because i am using 8 IR leds... i dont know weather i have an error in the following circuit or it is impossible to do..?

here is the circuit..

 

[Nigel Goodwin]

hi everybody,
i build this ir based proximity sensor...
all the components are on the same plane, so the IR receiver will only receive IR that is reflected on an object in front or the board..

But the results are not exactly what i expect, the range is really low: only 4 to 5 cm in best conditions!!!
it is strange because i am using 8 IR leds... i dont know weather i have an error in the following circuit or it is impossible to do..?

here is the circuit..

You need to amplify the signal from the IR diode, feeding it directly to a comparator is really going to restrict your range.

You also have a huge problem with external interference, the photo-diode will pick up ambient light and IR as well as the required signal. It's usual to modulate the IR transmissions, and use a receiver sensitive to the modulation frequency - you can get specially designed IR receiver IC's for just this purpose, used in TV's etc.

 

[ikalogic]

hi everybody,
i build this ir based proximity sensor...
all the components are on the same plane, so the IR receiver will only receive IR that is reflected on an object in front or the board..

But the results are not exactly what i expect, the range is really low: only 4 to 5 cm in best conditions!!!
it is strange because i am using 8 IR leds... i dont know weather i have an error in the following circuit or it is impossible to do..?

here is the circuit..

You need to amplify the signal from the IR diode, feeding it directly to a comparator is really going to restrict your range.

You also have a huge problem with external interference, the photo-diode will pick up ambient light and IR as well as the required signal. It's usual to modulate the IR transmissions, and use a receiver sensitive to the modulation frequency - you can get specially designed IR receiver IC's for just this purpose, used in TV's etc.

what to u suggest for amplification (simple transistor?)

 

[gerty]

The iondustrial photosensors we use all have a lens to capture the ir and focus it on the sensor..

 

[Jerran]

Ive had pretty good success using op amps to amplify IR detectors voltage.

 

[Nigel Goodwin]

what to u suggest for amplification (simple transistor?)

I would suggest opamps, it gives you easy control over gain and offset, but it's not likely to work very well unless you use modulation - unmodulated IR is too liable to interference.

 

[ikalogic]

it seems i have a big big mistake...

first i thought the component ir sensor i bought was a dual photo diode (3 pins & i use only 2) , like the ones found in computer mouses, but , after some searches on the net... i found this :
http://www.factorydirect.co.uk/factorydirectproducts/irproducts/irdetector.html#irreceivermodule
it is verry similar to the one bought, this componenent has a built in 38khz filter, maybe i need to modulate the ir comming from the leds...?? or in the other case i would have never had ANY signal from the sensor cause ther is no mudulation...??

IN OTHER WORDS:
is it possible that my sensor would be like the one found on this like, even thought i could get litle signal using only 2 pins ???

thx a lot

 

[Nigel Goodwin]

Re: it seems i have a big big mistake...

IN OTHER WORDS:
is it possible that my sensor would be like the one found on this like, even thought i could get litle signal using only 2 pins ???

If it looks like the one in the URL you gave, it's almost certainly an IR receiver IC and only receives a modulated signal. You will also need to connect all three pins, the output is a simple digital level - high for no signal, low for signal.