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 Forum index » DIY Hardware and Software » Developers' Corner
Some advice for lighting a random sequence of LEDs
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krabbacitor



Joined: Aug 13, 2009
Posts: 12
Location: Hamburg

PostPosted: Wed Nov 17, 2010 3:57 pm    Post subject: Some advice for lighting a random sequence of LEDs
Subject description: Voltage to coordinates...kind of
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Hi there!

OK, this is not really music related, but somehow this idea got stuck in my head and I don't really know how to do this...

I'd like to build a grid of LEDs, 5 by 5, which get randomly lit, one at a time, with a frequency of about 1 or 2 Hz, slowly fading, then another randomly chosen one.

I would like to do this without a microcontroller, so I thought of basing this on a noise source (zener or reverse biased transistor), some kind of sample (and hold) and a 555-clock. The timer triggers the sample and hold for a random voltage from the noise source.

Now I'm looking for an easy way to connect this random voltage with the grid of LEDs. So the basic question is (besides the question why I don't want to use a microcontroller): What would be some clever way to turn a random voltage level into a coordinate?

I thought about using 4066-switches or multiplexers, two timers and two noise sources, logics, etc...

Another idea is to actually use a timer to both cycle through the LEDs and sample the voltage continually at a higher frequency, lighting the actual LED if the sampled voltage crosses a specific threshold - so this would be based on chance but that's not what I want.

I'd be glad to hear some ideas from you!

Regards
Christian
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ian-s



Joined: Apr 01, 2004
Posts: 2669
Location: Auckland, New Zealand
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PostPosted: Wed Nov 17, 2010 5:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

maybe use a couple of bargraph drivers for row / column.

Not sure how you would get the columns working though.
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krabbacitor



Joined: Aug 13, 2009
Posts: 12
Location: Hamburg

PostPosted: Tue Nov 23, 2010 12:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

i just noticed that what i'd like to build is a kind of 16-channel-color-organ... still the main problem is how to "translate" random voltage levels into coordinates.

but maybe this is a way to go: timed sampling of a random voltage level, with a second timer acting as some kind of vco, followed by 16 (!!) bandpass filters, each one connected to an led-driver...

is this stupid or just overly complicated? this thingy will be a one shot, so it's not of the essence to make it elegant. i still don't want to use a microcontroller...


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DrJustice



Joined: Sep 13, 2004
Posts: 2114
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PostPosted: Fri Nov 26, 2010 11:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

krabbacitor wrote:
...i still don't want to use a microcontroller...

Why don't you want to use a microcontroller?

The solution you outlined requires a _lot_ of components - yes, it seems overly complicated to me.

A small and cheap uC (e.g. an 8 pin PIC or AVR) is the most natural and elegant solution for this job, driving a few daisy chained shift registers to power the LEDs. Alternatively, a similar uC in a larger package (typically 40 pin) would give you a cheap single chip solution.

DJ
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Tim Servo



Joined: Jul 16, 2006
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PostPosted: Sat Nov 27, 2010 1:13 am    Post subject: Some advice for lighting a random sequence of LEDs Reply with quote  Mark this post and the followings unread

I think using two LM3914 bar graph drivers (as suggested earlier) would be the way to go. I'd use the noise source and two sample/holds, one for the row, and one for the column. I'd alternate samples between the row and column drivers, and there you go. Might also be fun to feed two different LFOs into the row and column drivers.

Tim (Random is my middle name) Servo
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sneakthief



Joined: Jul 24, 2006
Posts: 569
Location: Berlin

PostPosted: Sat Nov 27, 2010 2:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

http://www.eleccircuit.com/led-oscilloscope-by-lm39144017/

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