[Answered] Reversed Infrared LED as IR sensor: poor idea?

[Redcap]

Greetings all

This year I found a fair amount of IR LED's in my X-mas stocking and am keen to start work on a very basic IR proximity sensor.

I've read that a reverse polarity LED can be used as a crude receiver, but gives rather poor feedback (current/voltage wise) and as such, to use one, you'd need to include an Op-Amp into the circuit to boost it to a usable level.


I have more than enough IR LED's, but no receivers.
I have some LM324N Op-Amp's to assist with the amplification.


What I'm wanting to know is:
Is it worth waiting/buying/harvesting proper receivers for the job
OR
Would it be efficient to try and do this with the reversed IR LED & LM324N [as I already have these on hand]

It's my 1st attempt at making such a sensor, so was wanting some feedback/opinions before proceeding.


Thanks in advance,
Redcap

P.S: Sorry if this is long winded :-/

[Fr0stAngel]

well it will work 'BUT' they will have very poor sensitivity, which in any case would hinder whatever you plan to do with them...the voltage drop will be noticeable only at real close range, which is normally useless for most apps.

[Redcap]

Much thanks for the feedback, Fr0st

the voltage drop will be noticeable only at real close range

If "real close range" is within 1-5 inches, it should be ok.
I have a feeling you mean < 1 inch, though...
I'm hoping to use it as a proximity sensor to make a robot turn when it nears an object.
Going to try and have the turning very tight, and the robot not so big  

well it will work 'BUT' they will have very poor sensitivity

Edit: Ok, I've actually built a crude sensor now with the IR LED and Op-Amp, it works the way I want, but yes, it's -very- poor, < 1/2 inch when an IR LED is pointed directly at it...

I'm going to try & improve on this circuit to see if I can manage a better range.
If anyone has suggestions or experience on how to do this, (or if it'd even possible without swapping out the IR LED for something else) I'd be very thankful.

[Soeren]

Hi,

What I'm wanting to know is:
Is it worth waiting/buying/harvesting proper receivers for the job
OR
Would it be efficient to try and do this with the reversed IR LED & LM324N [as I already have these on hand]

It's my 1st attempt at making such a sensor, so was wanting some feedback/opinions before proceeding.

Yes, it's definitely worth getting some photo transistors (for greatest sensitivity) or photo diodes (for max. speed, although I guess you won't need that).

Using an op-amp and an IR-emitter is possible but... Only a really viable solution if you have ample experience and using more components (i.e. higher parts count and lower reliability), needs a modulated signal for a usable result etc.

If you are impatient and have some metal encapsulated transistors (like BC107, BC108 or whatever may be available to you), remove the top (and nothing but) with a cutting disk on a "Dremel" and you have a photo transistor.

LM324 is a dinosaur and it's only marginally better than a 741, for your purpose. If you really wanna go with the op-amp, use a CMOS input op-amp. You need high gain, high impedance, low noise and high CMRR.

[Redcap]

Thank you very much Soeren for your clear answer and explanations

I'd say I -don't- have ample experience, so I think it best if I did hold off until I get the receptors XD

Thanks again,
Red