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'[PIC:] Controlling 8 bi-color LED'
2004\06\24@183846 by Anthony Van Herrewege

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Hi,

I'm in the process of drawing up the schematics of my next project, a preamp. I'd like to be able to see the selected input on the front panel and decided to use Multimec switches (http://www.mec.dk/billeder/8_619.jpg).

Because the preamp will have a tape loop output, I need to be able to see that as well on the front panel. I think bi-color leds (the ones with 2 pins, not those with 3, since they won't fit the switches) are the best for that.

The problem is that I can't figure out how to connect those 8 bi-color leds to a shift register. Is it possible to connect 8 bi-color leds to an 8-bit shift register and control all of them? I need to be able to turn them all on independently, but there never won't be more than 1 green & 1 red lighted (in case I use red/green bi-color ones of course). Is there any kind of matrix-style connection possible for this or do I have to resort to a 16-bit shift register? Note the fact that I need to light 1 green & 1 red led at the same time, so usual matrix arangements won't work.

Regards, Anthony Van Herrewege


Website: http://members.lycos.nl/anthonyvh


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2004\06\24@184713 by Spehro Pefhany

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At 03:39 PM 6/24/2004 -0700, you wrote:
>Hi,
>
>I'm in the process of drawing up the schematics of my next project, a
>preamp. I'd like to be able to see the selected input on the front panel
>and decided to use Multimec switches (http://www.mec.dk/billeder/8_619.jpg).
>
>Because the preamp will have a tape loop output, I need to be able to see
>that as well on the front panel. I think bi-color leds (the ones with 2
>pins, not those with 3, since they won't fit the switches) are the best
>for that.
>
>The problem is that I can't figure out how to connect those 8 bi-color
>leds to a shift register. Is it possible to connect 8 bi-color leds to an
>8-bit shift register and control all of them? I need to be able to turn
>them all on independently, but there never won't be more than 1 green & 1
>red lighted (in case I use red/green bi-color ones of course). Is there
>any kind of matrix-style connection possible for this or do I have to
>resort to a 16-bit shift register? Note the fact that I need to light 1
>green & 1 red led at the same time, so usual matrix arangements won't work.

Why don't you just use 5 PIC port pins?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
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2004\06\24@185958 by Jinx

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> or do I have to resort to a 16-bit shift register? Note the fact that I
> need to light 1 green & 1 red led at the same time, so usual matrix
> arangements won't work.

I *think* you would need 16 pins to control 8 * 2-pin LEDs. If so, you
could either connect 2 * 8-bit SRs serially and have each LED to an
adjacent pair of SR o/ps or use the SRs in parallel with the LEDs
between them (ie SR1d0 - LED+R - SR2d0), which amounts to the
same thing except 1 * 16-bit is a little simpler to i/f to

OTOH Maxim et al are always putting out new LED controller ICs

http://www.maxim-ic.com

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2004\06\24@214932 by Harry Pfeifer

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The two wire bi-colour LED's  usually require the supply voltage polarity to
be reversed to change the colour. To control them from a PIC would require
an H-pack (or bridge) configuration. One wire of the LED's to connect to a
voltage divider giving half supply voltage and the other wire to a pipolar
PIC  I/O pin so that when the PIC output goes high it gives polarity for red
and when low it gives polarity for green. You still have to work out how to
control the LED's when you want them both off.
An easier method might be to regonfigure your design so that tou can use 3
wire bi-colour led"s

   Regards     Harry
{Original Message removed}

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