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Programmable IR LED Flasher Circuit -- How to Build?

Discussion in 'Electronic Design' started by [email protected], Sep 10, 2006.

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  1. Guest

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

    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.
    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?

  3. Guest

    So it's a PIC microcontroller? Which one? What's the rest of the
  4. That's why they pay us the big bucks!
  5. Guest

  6. John Fields

    John Fields Guest

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

    You might get someone to work up a design for you, complete with
    schematic, bill of materials, and working source code, all for free,
    but I doubt it, since that what we get paid the big bucks to do.

    If you need some of the devices, why don't you just buy them?

    BTW, please bottom-post.
  7. Guest

    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

    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.
  8. Guest

    I have a better idea. Take your big bucks and shove them up your
    arrogant ass. BTW Johnny, please don't be a fucking smart ass. Have a
    nice day.
  9. On 10 Sep 2006 10:23:24 -0700, in
    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

  10. Guest

    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

    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

    Thanks for the helpful reply.
  11. Guest

    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)?
  12. On 10 Sep 2006 13:55:15 -0700, in
    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

  13. Guest

    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.
  14. On 10 Sep 2006 14:12:48 -0700, in
    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

  15. Donald

    Donald Guest

    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

  16. John Fields

    John Fields Guest

    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,
    hit the books, and start the process we've all had to go through in
    order to be able to help newbies like you on their way. Good luck,
    and have a nice day yourself, dumbass.
  17. Guest

    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.
  18. Guest

    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.
  19. Don Foreman

    Don Foreman Guest

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

    Don Foreman Guest

    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.
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