Re: Programmable IR LED Flasher Circuit -- How to Build?
- From: kpkilburn@xxxxxxxxx
- Date: 10 Sep 2006 13:50:38 -0700
First of all, death to the 9V battery. Design with AA cells.
Doesn't really matter. I was just going off of the design of the one
I've used.
Second, by sequence, you do mean the lights flash sequentially? Or is
there a cadence to the flashing?
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.
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.
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.
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.
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 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).
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).
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.
AAs would be ok. What's a boost converter?
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.
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.
.
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