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Topic: Multiple IR LED modulation (Read 1 time) previous topic - next topic

cromato

Hallo.
I want to make a sensor with 16 IR LEDs.
The 16 receivers have only to switch on-off.
My problem is that the receivers work with 38 kHz.
Is there any way to modulate these Led at once with 38 kHz continous?
1 Led 1,5V, 100mA. I have thought on 2 parallel series of 10 Leds.

Paul__B

"a sensor with 16 IR LEDs" eh?

Since LEDs are light emitters, how would they sense something?

Perhaps you need to explain what you actually want to do?

Is this somehow related to your other post?

septillion

If you what to make a IR remote, just Google it. There are multiple libraries available which do so.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Paul__B

No, he has another post which appears to describe the same project.

I gather he wishes to use IR beams for timing purposes, but unless he chooses to provide adequate detail of his project, it simply is not worth further speculation.

cromato

Yes, its the same project.
I want to make a sensor, somthing like a barrier of 16 ir leds and parallel to it 16 ir receivers.
I need to read every single receiver like a bit.
So i have 16 bits and look for fast changes to detect cracks on the edge of paper on a machine.

I thought on 16 IR receivers that works on 38 kHz, but now i need to modulate the IR Leds.
I dont need to send any data trough it, only the state of 0 and 1.

cromato

The IR Led i´ve found with angle of only 5°, 1.5V, 100 mA - Osram SFH4545
and the IR Receiver: Vishaj TSOP4038

Thanks for the answers!!

septillion

Yes, its the same project.
I want to make a sensor, somthing like a barrier of 16 ir leds and parallel to it 16 ir receivers.
I need to read every single receiver like a bit.
Okay, clear, uhu

So i have 16 bits and look for fast changes to detect cracks on the edge of paper on a machine.
Wait, whaaaaat  :o Cracks? Edge of what? Paper? Machine? How?

Dammit, I should have fixed my crystal ball this weekend.

And how fast is fast? 38kHz IR receivers for remotes are not extremely fast or anything. Have a look at the datasheet, see if it's fast enough.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

cromato

It is a paper machine. The paper web speed 10-15 mt/sec.
The cracks on the edge of the paper are small, so the IR receiver has to switch the signal faster
than 5 msec.

septillion

Then I would say, open up some datasheets and think about what the response time is you need. Especially for the whole system. Because what has to happen when a crack is spotted etc.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Paul__B

Right, now ...

Well, the TSOP4038 has a response time of under a millisecond, so it appears it will suit your application.  The modulated signal has the advantage of being substantially unaffected by ambient light, and you probably want that.

While an Arduino could generate the 38 kHz, it will probably be just as practical to use a 555 timer (CMOS version preferable).  You will need a transistor or FET to switch the LEDs, if you start with a 12 V supply, you could drive four parallel chains of four or with a 15 V supply, two parallel chains of 8 (a TS555 will operate at this voltage).

Chagrin

http://www.righto.com/2010/03/detecting-ir-beam-break-with-arduino-ir.html has the information you need. The TSOP4038 is the right choice for this application.

If you're dealing with distances under a meter you won't need anywhere near 100ma going through those IR emitters. Even 1ma should be plenty, and you should be able to parallel all 16 emitters (with a current limiting resistor on each) from a single Arduino pin (limit 20ma max). These IR receivers are very sensitive.

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