Random LED's

B

Bill

Guest
Does anyone know a good and simple way to have 4 LEDs blink in a random
pattern
 
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My preference for a simple way would be to use a PIC microcontroller
(pick your own preferred type here), and put something like a linear
congruential generator on it (see Wikipedia - generating a number
requires just a multiply and an add, if you let M be a power of 2).
Once you generate an 8-bit output, use the upper 4 bits for your LEDs
and throw away the lower 4 bits (the lower bits of a linear
congruential generator have awful randomness). With an appropriate
PIC, you can do this with literally nothing but the chip, a power
supply, the LEDs, and the current-limiting resistors. Something like
the 16F627A/16F628A/16F648A have a built-in oscillator and can run
from 3 to 5.5 volts, so 3 AA batteries would power the whole system.
You can also get the 16LF variant (instead of 16F) which can run down
to 2V, so you could use only 2 batteries. I'm not familiar with the
10F series, but you can probably find a 10F series PIC that'll do the
job just as well, and the 10F series have only 8 pins where the
16F648A has 18, so you'd use a lot less space.

On the other hand, if you've never done any microcontroller work, it's
a big job to get started.

Chris

Bill wrote:
Does anyone know a good and simple way to have 4 LEDs blink in a random
pattern
Click to expand...
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On Fri, 30 Jun 2006 17:24:36 +0000, Chris Head wrote:

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My preference for a simple way would be to use a PIC microcontroller
(pick your own preferred type here), and put something like a linear
congruential generator on it (see Wikipedia - generating a number
requires just a multiply and an add, if you let M be a power of 2).
Once you generate an 8-bit output, use the upper 4 bits for your LEDs
and throw away the lower 4 bits (the lower bits of a linear
congruential generator have awful randomness). With an appropriate
PIC, you can do this with literally nothing but the chip, a power
supply, the LEDs, and the current-limiting resistors. Something like
the 16F627A/16F628A/16F648A have a built-in oscillator and can run
from 3 to 5.5 volts, so 3 AA batteries would power the whole system.
You can also get the 16LF variant (instead of 16F) which can run down
to 2V, so you could use only 2 batteries. I'm not familiar with the
10F series, but you can probably find a 10F series PIC that'll do the
job just as well, and the 10F series have only 8 pins where the
16F648A has 18, so you'd use a lot less space.

On the other hand, if you've never done any microcontroller work, it's
a big job to get started.

Chris

Bill wrote:
Does anyone know a good and simple way to have 4 LEDs blink in a random
pattern

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Click to expand...
I have never used a PIC, do you have a Schematic?
 
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Unfortunately a schematic won't help. A PIC is a type of
microcontroller, so you have to write code and then burn it into the
chip. Writing the code requires a computer and programming knowledge,
and burning it into the chip requires specialized hardware (a
programmer). If you HAD these resources already available, a PIC would
be both easy and cheap. If you have to acquire any of the above, it
will be either difficult, expensive, or both, and I would suggest a
different approach (at this point I stop being able to help you, since
I don't know off-hand another way to solve your problem).

Chris

Bill wrote:
[snip]
I have never used a PIC, do you have a Schematic?


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On Fri, 30 Jun 2006 10:11:57 -0700, Bill <bill@glacierwa.com> wrote:

Does anyone know a good and simple way to have 4 LEDs blink in a random
pattern
Click to expand...
---
Learning to cross-post might be a good start.



--
John Fields
Professional Circuit Designer
 
"Chris Head" <chris2k01@hotmail.com> wrote in message
news:eek:7dpg.85747$I61.65769@clgrps13...
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My preference for a simple way would be to use a PIC microcontroller
(pick your own preferred type here), and put something like a linear
Click to expand...
cripes, why have the guys spend hundreds of dollars in development tools for
a single application.

simple solution, get 4 blinking LEDs, wire them in parallel. after an hour
they'll be random enough.
 
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Heh... because if you already HAVE the tools, because you do OTHER
things with microcontrollers, then it's only a few dollars, and the
solution is very small in terms of space taken up. I did say that if
you don't already have the tools and knowledge this probably isn't a
good idea.

Chris

Tater Schuld wrote:
"Chris Head" <chris2k01@hotmail.com> wrote in message
news:eek:7dpg.85747$I61.65769@clgrps13...
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My preference for a simple way would be to use a PIC microcontroller
(pick your own preferred type here), and put something like a linear

cripes, why have the guys spend hundreds of dollars in development
tools for
a single application.

simple solution, get 4 blinking LEDs, wire them in parallel. after an hour
they'll be random enough.
Click to expand...
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Bill wrote:
Does anyone know a good and simple way to have 4 LEDs blink in a random
pattern
I need some parameters. How random? Is the frequency of LED flashing to
Click to expand...
be low enough that it doesn't look like a blur to the eye?

Probably the best simple method, if you don't have a uP development
setup, is to have a 4-bit counter feeding the 4 LEDs (via current
buffers probably), and a high frequency (1MHz?) clock feeding it via a
gate so that it gets clocked for roughly 1mS and then sits with the
4-bit output reached for roughly 50mS, then counts again. So long as
the counting time is varying slightly (a 555 timer might be variable
enough by itself, but I'd suggest adding some simple radio output into
the timing - ask me if you need a circuit).

Mark.
 
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