Optical Sensor (different from the 2-d sensor)

Hi again. I am looking for an optical sensor, probably LED based, maybe laser diode, that can be mounted on a thin PCB. It needs to be fairly small. I am designing a small retroreflective system from inside a slot machined into a molding with a piece of reflective tape approx 3 ft away.

Any takers on this one?

Reply to
Howhurley
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LEDs and lasers both emit light.

Do you mean you want a sensor designed specifically for use with a retroreflector?

You're probably stuck with using a PIN photodiode and LED, and doing your own optics.

But your request is so vague it's impossible to tell.

How bright are the other lights in the room? How many of these devices will be in the room working together? Does it have to work while looking at it's brother right next to the reflective tape? How wide is the slot? How much accuracy can you pay for? Etc.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Usually, with that kind of distance, one uses a modulated light source and tuned detector: 40 kHz infrared diodes and integrated circuit receivers for this purpose are the mainstays of TV remote controls...

Reply to
whit3rd

Do you have any links to schematics? I'm mulling over making my own around-the-house repeater system. Though I have a number of ideas, starting point could be helpful.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

flective system from

If you can mask the light path so only the reflective tape is significantly illuminated, it's relatively easy. For this distance, a modulated IR LED source and tuned receiver (just like your TV remote control) are the easy solution.

Integrated remote control receiver chips tune for something like 40 kHz, and ignore stray light. PNA4602 is typical...

Reply to
whit3rd

What about a laser pointer? You can get one at a dollar store.

shortT

Reply to
shortT

How about a laser pointer. One you can buy at a dollar store.

shorT

Reply to
shortT

.

I want to project an LED or laser beam perpendicularly out of a .33 inch aluminum slot. I want to "see" the reflection from reflective tape. up to 3 ft away and tell when the beam is broken. I was thinking that I could modulate the frequency of the transmitter and use a uP with the capability to have a fairly small window so I can eliminate extraneous "noise."

I probably could put the detector on the opposite side instead of the tape.

I was also thinking, if I did that, I could use a couple line collimated lasers, frequency modulated, so an individual reciever would be able to tell if the source was interrupted.

Thanks again for your response.

Reply to
Howhurley

Sorta like the ones you can buy from Radio Shack, only smaller?

Should work.

I would try first with an LED or laser + a PIN photodiode. If you _really_ want to distinguish your signal from others you'll use a pseudo-noise sequence to turn the thing on and off; if you're sane you'll just use a fixed tone and hope that there's nothing else in the room on frequency.

You may have more of a challenge minimizing the coupling between the transmitter and receiver with no reflection than you do with anything else.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

flective system from

So, unless the light is focused and beamed, little will be sensed.

Your TV remote control easily handles this kind of problem: just modulate (about 40 kHz) the IR source, and use a tuned detector. The detectors are simple three-pin ICs with onboard signal conditioning, like Panasonic PNA4602.

Keeping the stray light under control, so the reflective target is the only item sensed, is a small matter of design...

(something is wonky in my newsreader, I've tried this reply twice before with no result - apologies if this is a duplicate).

Reply to
whit3rd

The first time I saw this, it was with an LM567/NE567 tone decoder used as the tuned detector:

is a similar application.

The linux remote control folk

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have a good selection of software and other tools for these tasks...

Reply to
whit3rd

I'd probably use a delta modulator to send audio.

But I'm only interested in remotes being usable all around the house.

My experiments with the IR-to-RF and RF-to-IR units available off-the-shelf have shown very poor to bad performance

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I had considered buying such several times. Due to poor reports that i read i always insisted on trying it in store. The sales critters were always surprised when it did not work.

Reply to
JosephKK

All of the current production stuff will have receiver overloads (bury the PIN photodiode) or will ignore a CW signal. Did stuff like that

15 years ago.
Reply to
JosephKK

I ordered from various web sites, but they all took them back.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Using the NE567 as a tuned detector only uses the 'lock' signal output (on pin #8); the example also piggybacked an FM signal and used the loop filter as a demodulator, which (while useful in its own right) is extraneous to the tuned-detector function.

Reply to
whit3rd

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