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Topic: Red laser and IR Receivers Yes/No? (Read 789 times) previous topic - next topic

Rustie0125

Nov 12, 2013, 12:32 pm Last Edit: Nov 12, 2013, 12:38 pm by Rustie0125 Reason: 1
Guys simple question.

If i shine a red laser beam into a normal 2 leg IR receiver will i be able to detect n HIGH or n LOW? i know about all the wave lenghts and and and but i don not want to modulate or transmit data just 1/0 detection

any idea?
He who does not try ,does not fail ,does not learn not to fail again http://powerduino.blogspot.com/

cjdelphi

yeah why not, you it depends largely on distance.. if it's a weak signal you could use a transistor to switch a logic high for you.


Rustie0125

I want to use a 5mw laser and max distance will maybe be 20 meters
He who does not try ,does not fail ,does not learn not to fail again http://powerduino.blogspot.com/

jremington

#3
Nov 12, 2013, 05:07 pm Last Edit: Nov 12, 2013, 05:09 pm by jremington Reason: 1
You will have to test it and see. IR LEDs and photodiodes are rather wavelength sensitive and some don't react to visible light at all. They are also usually covered with plastic that absorbs visible light. Photodiodes designed for the purpose are sensitive to a much wider range of wavelengths.

You can use a red LED to detect red laser light but they respond to light that is somewhat "bluer" than their emission. The following graph shows what I mean (taken from a publication by Forrest Mims):

Edit: on this graph, a red laser (around 630-650 nm emission) will be far to the left
"It seems to run on some form of electricity"

polymorph

What is a "2 leg IR receiver"? Do you mean a photodiode? Even from IR, that will be a very weak signal.

Didn't we just discuss exactly this question a few weeks ago?
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

tylernt

What is a "2 leg IR receiver"? Do you mean a photodiode? Even from IR, that will be a very weak signal.


I use this circuit:

http://www.fiz-ix.com/2013/04/ir-photodiode-circuit-schematic/

With analogRead(), it can detect IR from an LED reflected off my hand at ~8 inches. It does receive a bit of spurious noise though (1M pullup is pretty weak, and using a stronger pullup drastically reduces sensitivity), which I filter in software (wait for 10 unbroken 'hits') to get a synthesized HIGH or LOW.

If you aimed a 5mw laser right at a photodiode, that should be some pretty intense light even at 20m so even if red is a bit outside the IR range, I'd imagine the photodiode would probably pick it up. You'll have to tweak the analogRead() threshold of course and possibly even the pullup resistor value a little.

polymorph

Only way to know for sure, is to try it.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

tylernt


Only way to know for sure, is to try it.
Definitely. I think it has a chance but make no promises. ;)

polymorph

Wouldn't this be simpler with an IR LED focused down, with the red LASER as a visible indication of where it is aimed? Or use a visible photodiode or phototransistor, with a deep red plastic cover over it?
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

123Splat

Use a DPSS green LASER module instaed.  Green is more visible and Green DPSS uses an I.R. pump diode with A LOT of bleed through of the I.R.

Really, Polymorph's I.R. LED suggestion is a better idea.  Forget the red LASER.

Chagrin



Only way to know for sure, is to try it.
Definitely. I think it has a chance but make no promises. ;)

I'll make a promise it'll work (with red).

The intensity of a laser is much greater than any IR LED so when you're looking at the spectral sensitivity graph even the slightest bit of sensitivity will be enough.

MarkT

If the IR photodiode has a clear lens it will see red photons and response to them as they
are of a higher energy.  In general the shorter the wavelength the higher the energy so
blue photons trigger green or red LEDs as photodiodes, but red photos may do nothing
at all to a blue LED used as a photodiode.  All to do with quantum mechanics and
semiconductor band-gaps.

With a blackened lens most of the visible is filtered out so it all depends how much gets
through (which depends on the dye used and the emission spectrum of the laser).  IR
photodiodes for consumer equipment tend to have black filters so they are not blinded
by sunlight or nearby lamps.
[ I won't respond to messages, use the forum please ]

zoomkat

In an almost identical discussion I suggested one might carefully sand down the lens/filter to let more visible light in.
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

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