Re: Programmable IR LED Flasher Circuit -- How to Build?


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

http://www.ownthenight.com/html/Products/Illuminators/illphoenix.html

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.

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.

.

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