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transistorboy32
06-08-2005, 12:27 PM
Hey everyone -
I'm trying to design a fireworks display for the 4th of July with
the BS2p24 and a program on the computer which will be written in
Visual Basic. The idea is to have 100 or so fireworks shoot off to
the beat of music playing from the computer. The program would have
3 "modes": Learn, Edit, and Play. The Learn mode would be used for
calculating exactly how much time it takes between the time the
computer sends out the data to the Stamp and the time the firework
explosion sound gets to the microphone (for each type of firework).
The Edit mode is used for working with the music and placing each
firework burst with the beat of the music. The Play mode puts both
previous modes together and actually shoots off the fireworks while
playing the music.

I've been looking for a cheap but effective way to control ~100
individual outputs that will be used to trigger the fireworks. I was
thinking about using small coils of Nichrome wire that would fit
around the fuse of each firework to ignite it, and a pair of 8
digit, 7-segment LED driver chips (such as the MAX7219CNG)
interfaced to the BS2p24 and finally to the computer to control it
all. I realize that the Nichrome wire would take more current than
the LED driver would supply, but I'm not sure what to use to go in-
between the drivers and the Nichrome. Would a Darlington transistor
array (like the ULN2003) work? The MAX7219CNG has a matrix-style
output with "rows"(ie digit 1-8) supplying the negative
and "columns"(ie segment 1-7) supplying the positive to activate a
certain LED, and I'm not quite sure how to address this.

This is an idea I had last 4th of July and it would be great if
anyone has any insight as to how to make it work for this year!
Thanks!

-Seth

Jon Williams
06-08-2005, 07:10 PM
If I were doing this, I would not use any kind of multiplexer; I'd use a device with direct DC outputs and run them through a high-current driver like the ULN2803.

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Jon Williams
Applications Engineer, Parallax

transistorboy32
06-09-2005, 10:47 AM
What kind of device would you suggest? All I can think of is a set (14 or so) of 8-output serial-to-parallel shift registers. If I used the same data & clock signals for all chips and used the chip select, I'd still need more outputs on the Stamp. I could use yet another pair of shift registers to use on the chip select lines, but that seems like a lot of extra wiring. That's one reason I considered using two 64-output LED drivers. Is there a device out there that has more than the standard 8-outputs to reduce the chip count? Again, thanks for the help!

Paul Baker
06-09-2005, 11:10 AM
Jon is refering to a (de)multiplexer, given a N bit number switch one of 2N outputs, an example part is the 74HC154 (http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/CD74HC(T)154.pdf)·which takes a 4 bit number and switches the corresponding output (of 16 possible). You can get more out by cascading them, a simple example of using 3 1:2 decoders to form a 2:4 decoder:


___ ___| |-- 0
___ / |1:2|
| |---/ |___|-- 1
---|1:2| ___
|___|---\ | |-- 2
\___|1:2|
^ |___|-- 3
|
MSB ^
|
LSB


Post Edited (Paul Baker) : 6/9/2005 4:18:59 AM GMT

Jon Williams
06-09-2005, 11:38 AM
I was refering to a simple shift register like the 74HC595 which can be daisy-chained. This would let you fire multiple output simultaneously and in perfect sync since the internal registers are not transfered to the outputs until the Latch line is pulsed.

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Jon Williams
Applications Engineer, Parallax

Paul Baker
06-09-2005, 06:55 PM
Argh, sorry Jon, thats what happens when you miss a single word like "not", please disregard my previous post.

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