Programmable IR LED Flasher Circuit -- How to Build?

I'm trying to build an LED flasher (as small as possible -- operating on a 9V battery) like this...

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Here's how it works...

You attach it to the battery then program the flash sequence by shorting the terminals on top. Once you first short the terminals, the time starts counting and you have a specified amount of time (about 5-6 seconds) to program a sequence. As you short the terminals, you see a visible green LED that indicates on. You tap out your sequence and when the time is up, it stops accepting programming.

If you view it through night-vision scopes, you can see the pattern you input flashing in IR.

From the look of the commercial device, there are only 2 ICs, both of

which I'm assuming are simple off-the-shelf logic (could be a bad assumption). I had originally thought 555 timer and shift register.

My idea for the design was that a timer clocks in your input to a shift register. The longer you short the terminals, the more 1s are clocked in. This results in a pattern of varying pulse widths that can then keep cycling through the shift register and illuminate the LEDs.

I was unable to find similar circuits on the web, so I'm not sure that's the right approach. I had although thought of individual one-shots somehow keeping the outputs high/low with something clocking them to change it based on what you input.

I can't figure out the "memory" of it, but I'd assume it's not something complex -- that's why I keep thinking "shift register". For it to work though, it would have to be many bits wide. I found some

8-pin ICs that have 16-bit serial registers in them, so if the duration of the one-shots output is 1/3 second, then the shift register would support a 5-second programming duration.

Any ideas?

Thanks.

Reply to
kpkilburn
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Microchip.com

Reply to
Homer J Simpson

Reply to
kpkilburn

That's why they pay us the big bucks!

Reply to
Homer J Simpson

What?

Homer J Simps>

Reply to
kpkilburn

--
Yup, that\'s why they pay us the big bucks.

You might get someone to work up a design for you, complete with
 Click to see the full signature
Reply to
John Fields

First of all, death to the 9V battery. Design with AA cells.

Second, by sequence, you do mean the lights flash sequentially? Or is there a cadence to the flashing? I doubt you could see an individual LED from any distance, so a pattern of flashing would be dumb. Cadence is another story. That you could detect over distance.

While a shift register would work, all you are really building is a state machine. This can be done with D flip flops and an EPROM. Some of the address lines would be used in making the state machine, and others would be used in selecting the cadence pattern. One bit in the memory needs to be reserved for LED on or off. Just write out the K-amp by hand, then program the memory (assuming you can find a burner).

I'd suggest designing a current source to feed the leds. This will keep the light output uniform as the battery is drained. You could use two AA cells and a boost converter instead of the 9V battery. Your choice, but two AA cells are the same size as a 9V battery, but have much more juice.

I built a cheesy IR flasher by taking a made in China red led flasher and replacing the visible leds with IR leds. The Chinese design was so bad that they paralleled the LEDs. I guess they don't know about current hogging in China.

Hint: This isn't a big bucks design. High school kids in the valley can do this.

Reply to
miso

I have a better idea. Take your big bucks and shove them up your arrogant ass. BTW Johnny, please don't be a f****ng smart ass. Have a nice day.

John Fields wrote:

Reply to
kpkilburn

There is no "rest of the circuit", it is all written basically as a text file ( source code), and translated so the pic (bletch) can understand it

You can download the stuff from microchip, and read through it, and learn to do it yourself, it take time and patience they you will be able to say, maybe

"That's why they pay us the big bucks!"

Thats why source code is not available on isohunt

martin

Reply to
martin griffith

Doesn't really matter. I was just going off of the design of the one I've used.

It's a programmable blinking pattern. I guess sequence was the wrong word. Whatever you tap out on the leads is repeated (about a 5-second period that repeats). You can actually see it from quite a ways off. The one that I've used (Phoenix Beacon) has 3 LEDs in it. When you're looking through night vision devices, you can see it.

It's for assembling on a drop zone at night. When you have multiple units in the area and it's dark, a pattern of flashing is very useful. OK, cadence too. For example, it's long-long-short for one unit. Short-short-short for another. So by pattern, I mean long and short bursts.

Isn't a shift register just flip flops strung together? Or would it be better to use them individually? I was just assuming shift register. It's been years since I've done anything like this.

Some of

The device has to be "field programmable". You short the two leads and it starts a 5-second time period. Whatever you tap goes into "memory" and then that pattern repeats indefinitely (or until the battery dies).

AAs would be ok. What's a boost converter?

:-)

I figured as much. That's why I don't want to spend $70-80 on something like this if I can build it. Plus, I just want to see how it works.

Thanks for the helpful reply.

Reply to
kpkilburn

But how would you program it? The device I have used (Phoenix Beacon) has two leads on it. You tap out your sequence by shorting the leads. You have about 5 seconds from the first time you touch them. Whatever you tap out then repeats indefinitely.

I've never worked with PICs before. Does it have an "input" (something you can apply voltage to/ground that would put pulses into the PICs memory and then output the pattern to an LED)?

Reply to
kpkilburn

I'm not familiar with pics, its just a microprocessor,

1) you have to create/write a program for the appropiate micro, see the microchip site. You define when you write the program what the pins on the micro do, input or output, maybe both. 2) you then burn the program into the micro 3) then you have fun

martin

Reply to
martin griffith

I thought it was called a PIC, but I went back and looked and see that PIC is the trademarked name for the microcontroller.

I guess I have some reading to do. I never really thought to do something like this. I had assumed that the beacon was simply built with "simple" logic parts (gates, counters, shift registers).

Thanks for the replies.

Reply to
kpkilburn

Its changed, these days it is easier to program a pic than work out a

555 circuit,because you immense flexibility. For a little project like this, (when you get a cheap 99$ development kit) the most simple program will take 5 minutes, but it can be a steep learning curve.

google piclist

martin

Reply to
martin griffith

For $25, you would be hard pressed to make your own for less. For $85, you would still need a good reason to build just a few.

Like many here, I have parts on hand to build such a device. But, do I have the time it would take, or do I want to spend the time making such a thing. ( even if I did know what it would be used for )

If this is an learning project in building such devices, you have everything you would need in the following posts.

So what are your goal ?

Are you looking to build a bunch of these, or just one or two ?

Good Luck

donald

Reply to
Donald

--
Well, now that you\'ve had a little taste of reality and you realize
that you don\'t know squat, I guess you\'ll unruffle your feathers,
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Reply to
John Fields

A taste of reality? Ha! I live in a much more real world than you johnny boy. I don't have to be an arrogant prick just to boost my self esteem. Come with that type of attitude to my side of the fence and see if you don't just get bitch slapped into the middle of next week. (And before you go crying and say that I threatened you, I didn't. I somehow picture you as that type of guy -- sit behind your computer terminal and brag about yourself, but wither like a pansy when the real world smacks you down).

Anyway Johnny, run along and play with your toys. I've grown tired of this juvenile little game and probably shouldn't have entertained you this long. You probably have some sort of weird fetish and get off when people exchange things like this. I want no part of your perverse little world.

Reply to
kpkilburn

Mainly just learning. I was looking for some ideas on how to implement it relatively easy. Yeah, I could spend days and weeks studying, but beyond this project, I'm not sure I'd do much more.

One or two. I have a big budget, so I could just buy them, but it would be a nice to make a few for the learning experience and as a nice conversation piece.

Reply to
kpkilburn

He does have a point. If you don't want to be helpful, why not just ignore him?

Reply to
Don Foreman

Hey, you asked the question! You must expect some of that in an open newsgroup. Best not to get yer knickers in a knot when it happens, because it *will* happen. Ignore the chaff, there really are a few helpful contributors here.

While having a beer with some buds at the lake this weekend, one of them observed that engineers are a bunch of arrogant assholes. I broke out laughing -- because I couldn't disagree with him. Stereotypes like that don't exist without a reason. I worked with plenty of them when I did it for a living. Some of the good ones were arrogant, but most of the best ones were not. They didn't need to be. Engineers work hard, long and constantly to learn their profession and keep current, and it can be very competitive at times -- so arrogance sometimes becomes a defense mechanism. I worked with dozens of PhD's every day. All save two or three were arrogant to some degree. The two or three that were not are world-class in their fields. An arrogant or vague response is often a way to avoid saying "I don't know", or "I don't want you to know how simple it really is". You do not want an engineer watching your six in most engrng orgs.

Your flasher dingus is very likely based on a simple low-end microcontroller. There are several ways in which it might work. One way might be to divide up the 5-second "programming time" into a number of windows, say 64 or 128 depending on how much memory the microcontroller has. It then checks periodically to see if the user is telling it to turn the LED "on" or "off" during the next short time period. It stores this information in its RAM (random access memory). In use, it just plays back the sequence it learned.

These devices are quite easy to use once one has learned how to use them. It is not difficult to learn in the sense of requiring a lot of technical background, but it isn't trivial either. A high school kid can do it if he or she is motivated enough to do so. Having a mentor or taking a course or seminar can help a great deal. Most young engineers today are quite adept at writing software for these gadgets, even though their grasp of basic engineering principles often seems to be quite sketchy.

Reply to
Don Foreman

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