From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Fri, 5 Jun 2020 03:45:20 -0700
Subject: Re: [EE] Detecting a change of level on four lines with digital
	logic/analog circuitry?
Thread-Topic: [EE] Detecting a change of level on four lines with digital
	logic/analog circuitry?
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Hi David,

I'm not permitted to use programmable electronic devices. I agree that it
would be a perfect application if they were allowed.

Latency of up to 20ms permissible.

On Friday, June 5, 2020, David C Brown <dcb.home@gmail.com> wrote:

> How much latency is acceptable.  And is the output pulse retriggerable.
>
> Would using an 8 pin PIC to sample and digitally compare the inputs be to=
o
> slow?
> With a 32MHz part you would be able  to keep the latency under a micro
> second.
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: dcb.home@gmail.com
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
>
> On Thu, 4 Jun 2020 at 21:38, Jason White <whitewaterssoftwareinfo@
> gmail.com>
> wrote:
>
> > Hi everyone,
> >
> > I have an application where I need to generate at pulse least 1
> microsecond
> > long any time a rising or falling edge is detected on four digital line=
s.
> > The four signals can change at any time to any direction. The pulse is
> used
> > to trigger a timer providing a reset signal to the rest of the system.
> > Microcontrollers and programmable logic devices aren't allowed.
> >
> > Four 74HC123s will do it, but are too big.
> > Four window comparators monitoring the signal through an RC will do it,
> but
> > also seems too big.
> >
> > Is four schmitt trigger XOR gates with four RC's the smallest
> > implementation?
> >
> > I was thinking some sort of analog implementation might be able to do i=
t
> > smaller. But AC coupling the four signals together would allow them to
> > cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> > better?
> >
> > Regards,
> > Jason White
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
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> >
> --
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--=20
Jason White
--=20
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