That sounds like a great solution, but what chips should i use to count
the clock? I could use PICs or are there cheaper ones?

bye

On Tue, 29 May 2001, Gennette, Bruce wrote:

> How about a 3 pin solution?
>
> It'll cost you a few external chips, but its expandable (and cheap).
>
> Ok - all detector inputs come through a bunch of OR gates (small signal
> diodes) to ONE input.
> One output pin clocks through cascaded decade counters, each output of which
> fires up an LED in your light barriers one-at-a-time.  The third output
> resets the counters for guaranteed synchronisation at the start of each
> cycle.
>
> Your software resets the external counter chips and an internal counter is
> set to 0. You wait a small settling time then read in the value of light
> barrier #0.  Next you pulse the counter clock, increment the internal
> counter and wait for light barrier #1 to settle.  Read #1 and move on to the
> next . . .
>
> Rise time for LEDs is pretty fast, so this would probaly be Ok for around 20
> light barriers.  For more just parallel the clock and reset to each decade
> counter and dedicate an input to each set of 10 light barriers connected to
> each decade counter.  Pin count is 2 + (light barriers / 10).  You read each
> input after the settle time then clock all the paralleled counters together.
>
> Bye.
>
>
>
> -----Original Message-----
> From: Thomas Graf [mailto:piclist@JPYNET.DYNDNS.ORG]
> Sent: 29 May 2001 08:19
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: To few pins
>
>
> Hi!
> I have the problem that i need about 60 i/o-pins, but i just have a 16c67
> and so i just have 33...
> I have to check a lot of light barriers, so is there something with
> multiplexing or something?
> What is a usual way to manage this?
> ciao
>
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