Re: Controlling hundreds of LEDs

From: CFoley1064 (cfoley1064_at_aol.com)
Date: 12/22/04 

Date: 22 Dec 2004 14:17:04 GMT

>Subject: Re: Controlling hundreds of LEDs
>From: Danny T danny@nospam.oops
>Date: 12/22/2004 4:54 AM Central Standard Time
>Message-id: <41c9527a$0$46667$ed2619ec@ptn-nntp-reader01.plus.net>
>

>Right, I think I understand - except for what you've labelled as SQ8 on
>your diagram. Does this hold the "last" bit that's about to be dropped?
>(and does this work based on the clock pin, and not the latch?) So if I
>sent 16 bits (clocking active in between each), and *then* latch, would
>I get 16 unique outputs, which I can then redraw before the next latch?
>
>Think this will be the easiest way, though I don't know how fast I can
>shift the data (300 LEDs is more than 600 outputs)!
>
>Thanks,
>
>Danny
>
>

If you've got an 8-bit shift register, what happens when you shift in the 9th
bit? The joke is, "It falls into the Bit Bucket, of course", meaning it
disappears out the end. Seriously, if you've got a line of serial data, you
can chain 8-bit shift registers so the first bit is shifted into the second IC
when the 9th bit is shifted in. It's a simple shift register concept, and the
SQ8 pin on the '595 is where you either put the bit bucket (;-) or you put
another shift register IC.

If you're doing 5X7 matrix displays, you don't have access to all 70 LED pins
anyway. You have to address them as row/column. If you do it that way, you
will minimize the shift register outputs. But, like the professional displays,
you then have to be concerned about a multiplexing setup where you use
persistence of vision to go across the columns fast enough that they don't
appear to flicker.

I've been following the flurry of posts here, and it seems like you've got a
ways to go on your understanding of the hardware end of things. If you want to
do a project over the holidays, possibly you might want to consider a smaller
concept (like one alphanumeric character display) until your hardware
capabilities catch up to your software skills.

Good luck
Chris

Relevant Pages

  • Re: Looking for simple way to interface BCD to serial (RS232)
    ... that's 900 characters a second through a 30 character/second pipe. ... Wait for leading edge of address pin 1 ... Load digit 1 in shift register and shift it out ...
    (sci.electronics.design)
  • Re: Just one pin to control a shift register
    ... My design might not be brilliant, but I hope it will work in the end. ... Jumper a pin from the PIC to the SR so that you clock it properly. ... The first pin would go to the actual shift register ...
    (comp.arch.embedded)
  • Re: Loss of synchronisation: Are the chips reliable?
    ... My college project this year was to make a Connect4 game consisting of ... Reset the shift register to all zeroes ... The method of using one pin would be implemented by feeding the ...
    (comp.arch.embedded)
  • Single pin to control a shift register
    ... I have an 8-Bit shift register chip, and at any time there will only ... Each shift-register pin will go to a single LED, ... micrcontroller boots up, I would put a HIGH onto the input, clock it, ... On the input to the shift register, I put an OR gate. ...
    (comp.arch.embedded)
  • Just one pin to control a shift register
    ... I have an 8-Bit shift register chip, and at any time there will only ... Each shift-register pin will go to a single LED, ... micrcontroller boots up, I would put a HIGH onto the input, clock it, ... On the input to the shift register, I put an OR gate. ...
    (comp.arch.embedded)