IR LED direction accuracy

I plotted a TSAL6100 today and posted the patterns at the end of <

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Second pattern is LED rotated 90-degrees.

Actually a pretty good pattern for a LED, I've seen some really ugly ones. I've used these LEDs before - lot of power and narrow beamwidth in a small package. Steve Noll | The Used Hi Tech Equipment Dealer Directory: |

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And you know that because?

Rather than brute force this design with power, have you considered modulating the led rather than just a pulse, and then improve the detection by using a filter on the received signal. The essence of any communications scheme is apriori knowledge of the signal. Say the goal was a 10uS pulse. Suppose the beam was modulated with a CW (plus DC offset to keep the led on) at 1MHz. On the receiving end, set up a detector with some basic AGC and then a filter at 1Mhz. Do an energy detection on the filtered signal, which could be as simple as rectification and DC filtering.

I wouldn't go pointing lasers into the aether unless you know it is safe. [The military targets with a class IV laser, which sounds kind of dangerous to me, until you consider what is coming next.]

spend a few bucks for a "keyring" laser pointer. visible's light's much easier to aim than IR.

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?? 100% natural

My intention, if I do decide to use IR, is to use a standard remote control receiver module. I have some experience with this and it already has all the features you mentioned - amplification, AGC, frequency tuning, noise suppression. What needs to be tackled is the problem of making the system work at long distance.

There's that to consider, of course.

In a way, yes. But hitting the target at 400m with a beam some inches across won't be easy, and a mild bump could easily make it go out of alignment again. OTOH, an IR LED, even the narrow-angle type I have in mind throws a much wider beam, the 90% intensity circle being more than 50m across at 400m.

No chance of getting those where I live.

Ah, but I need a much faster response than that - of the order of

1msec.

Thanks. Somehow it hadn't yet occurred to me to look it up on Wiki or other sources on the net. I've saved the image for future reference.

I'll report my progress here. But it will be some time before I have a chance to try it out. Thanks for your continued interest.

Thanks. That's a big help. It answers my original question very nicely. Your measured patterns correspond quite well with the idealized pattern in the datasheet.

I've already considered that aspect. The transmitter and receiver will be placed atop 12-ft towers. The TSAL6100 has a much reduced radiation at 15 degrees off axis, and practically none at 20 deg. By the time the off-axis radiation has angled down enough to reach eye level, it will be at some distance from the transmitter tower and the radiation will be much less intense. Placing the emitters in a tube will further increase the minimum distance from which bystanders can look directly at the IR source.

Correct me if I'm wrong, but I think that's for lasers. An IR LED radiates to a much wider angle and the intensity per unit area dissipates much more quickly with distance.

Maybe. I'm still weighing the pros and cons of each against the other.

I'm exploring that too. But while I'm no expert on such systems, it seems that they are rather slow for the 1msec response time I need.

"Pimpom" wrote in news:igflq2$tn4$1 @news.albasani.net:

If your using an off the shelf IR detector like the PNA4602M it's a

38kHz carrier modulated at about 1.25kHz. Most IR detectors are around 38 kHz to 40 kHz modulated.

For a pulsed square waveform you can just use fig2 to ensure you don't exceed the rated maximum permissible average current for your worst case ambient. I know you won't get the 1000 mW/sr at the pulse widths but it will still be stronger. Anyways that's what I did a couple of years ago using the TSAL6100 and the PNA4602M and it easily went across my front yard about 70ft. I didn't test the maximum range but I've read of people getting very long ranges using similar primitive setups.

For best results if you're using a detector use a precision clock source I used a PIC clocked with a crystal. Not so critical for short range but if you want to get maximum range you want it to be bang on 38kHz or whatever your detectors carrier is. Match your LED to your detectors wavelength.

If you're not doing continuous transmission you could increase the duration of the 1A pulses increasing the mW/sr unfortunately they don't show a graph of mW/sr of current vs PW.

If you Google TSAL6100 you should find a few projects done with it, it's a pretty popular IR led.I think they are used in laser tag at pretty long ranges; with a lense though.

Off the shelf detectors have built in lenses that also filter the ambient lighting if I Remember correctly. Thats the black lense material over the IR RCVR on your TV for example.

Yeah a 1mW laser, but 1 mW into the eye in any form of 'light' will damage it. The eye pupil is (about 1mm^2 ?). Then sunlight 1kW/m^2 gives about 1mW into the eye. If you didn't blink when looking at the sun you would damage your eyes... If your IR has a similar intensity then there is the potential for damage... It doesn't have to be a laser... ever look at some of those new white LED's.... ouch!

It was years ago that I played around with RC stuff. And yeah no speed was needed, but 1ms sounds pretty easy in principle.

George H.

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Yes, I'll use off the shelf receivers _if_ I use an IR system, and I have some experience with them. This is a one-off (but important) project and I don't want to have to design the receiver unit from scratch. The PNA4602M seems to be a popular model and I already have a datasheet from a few years ago. The problem is that I don't know of a source for it here in India.

I've been comparing the 4602M with some Vishay products, but they use different speccing methods for sensitivity. Converting one to the other is a bit of a PITA. Vishay use their TSAL6200 emitter at a specified drive level as a standard source. Panasonic use a photodiode of known sensitivity to calibrate the output of an IR emitter at 20 cm., and then specify how far their receivers can detect that emitter.

Unless I made a mistake somewhere in the conversion process, the Vishay receiver modules appear to be considerably more sensitive than the 4602M.

In earlier, less demanding designs, I used RC oscillators, with the basic carrier chopped at integral sub-multiples of the carrier frequency. For this project, I was thinking of using a

455 kHz resonator with a 1/12 counter.

That's one of my reasons for using a readymade module. The built-in lens-filter blocks much (though not all) of unwanted radiation.

Pimpom Inscribed thus:

Maybe silly idea but if you only need a single event, a flash tube would give a far more intense optical signal but would the detector be able to respond quickly enough.

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Best Regards:
                     Baron.

Define frequency tuning and noise suppression in your mind. I doubt you have created a system like I describe, since it has noise immunity.

If you are just feeding pulses rather than trying to get clever, your only choice is brighter pulses. That is go for brute force rather than elegance.

The off-the-shelf receivers I have used have these features: Defined carrier frequencies, AGC, optical filter, lens Minimum & maximum number of pulses in a burst as well as minimum gap length between bursts - they reject signals that do not conform to this.

I found the required signal format by trial and error as I have no datasheet for the Chinese-made ones I bought from the local market. I contacted the manufacturers but they told me that they have no datasheet in English. I expect to get better performance, mainly longer range, using parts with known characteristics.

If you mean sending coded data with error correction and recovering missing pulses, etc., I guess you're right.

No, the problem is just amount of power intercepted by the eye, that it doesn't know to respond to. A single IR LED may not provide that much danger, but when you mass them, the total power radiated becomes very dangerous. I worked with IR illuminators back in the early 90's that had very strict warnings to maintain distance when activated. Think about the power differences available now as compared with 15 years ago, and you see the danger!

Charlie

It's mainly the power density on the retina that matters. Lasers get focused down to a very small spot, but LEDs don't, so the damage thresholds are quite different and depend on the spatial coherence of the source. If you want the OP to be safe, you should direct him to sources of reliable info rather than making stuff up.

Besides, IR LEDs haven't improved like visible ones--I have some from about 1991 that have more than 30% quantum efficiency.

Cheers

Phil Hobbs

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