From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Fri, 5 Jun 2020 03:53:58 -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?
Thread-Index: AdY7KLq//V5IqEoxTAe9qwhbMYRgJQ==
Message-ID:
 <CAOFvGD5gxDb-hjBfjva93yMGN=D42gAxsG4p5Zbz+sfzgvUfOw@mail.gmail.com>
References:
 <CAOFvGD5GusjBoy3p5dOWb_EHiVUC7VURMsyLi+UQX3pc8Tc0=Q@mail.gmail.com>
	<CAKsZx=0kOhnTsOois3ZzgWDt_v1Py0-=qtLe45tugPrv4zWUqw@mail.gmail.com>
In-Reply-To:
 <CAKsZx=0kOhnTsOois3ZzgWDt_v1Py0-=qtLe45tugPrv4zWUqw@mail.gmail.com>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: Pass
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: Pass (protection.outlook.com: domain of gmail.com designates
	209.85.218.54 as permitted sender) receiver=protection.outlook.com;
	client-ip=209.85.218.54; helo=mail-ej1-f54.google.com;
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com;
 s=20161025;
	h=mime-version:in-reply-to:references:from:date:message-id:subject:to;
 	bh=HPCJ5lNwhqCZBzD0IVVkX3IprErznWCWvn2KGc6IUk8=;
	b=dKre70qzgltqYnToRslZDHrcoK5O++m2U+/xD5X3wbkpxu9082STRpYSBvEEKuvMrQ
	K1jMwsIhTz1tUBLt+kvyc3PYrxQpTbRnVq0wFR5gkxcmD9T5mjbaailEC03vnpsLLTfS
	G0LpgomfyUGCf9PTF0GUW1G9paAO8uyFy2CST1zzG7laMq7kKgKX2BlcVhPimafhVlg/
	vD9pnNRAvoHyNHXe7l7f7BEUdJOBExO2uP6VHB8EWt3TbuPPKAreqhfs1GQwvHk9C7F0
	4wBnP/ze4eA5K5nzJDswPcUncRcYJhqHmbM3ll5v3+cyqJR5pubN58AluC1cwAILw6Qs	eXXw==
authentication-results: spf=pass (sender IP is 209.85.218.54)
	smtp.mailfrom=gmail.com; mit.edu; dkim=pass (signature was verified)
	header.d=gmail.com;mit.edu; dmarc=pass action=none
	header.from=gmail.com;compauth=pass reason=100
errors-to: piclist-bounces@mit.edu
list-id: "Microcontroller discussion list - Public." <piclist.mit.edu>
list-post: <mailto:piclist@mit.edu>
x-beenthere: piclist@mit.edu
x-mailman-version: 2.1.6
x-received: by 2002:a17:906:470c:: with SMTP id
	y12mr8325989ejq.336.1591354439181; 	Fri, 05 Jun 2020 03:53:59 -0700 (PDT)
x-topics: [EE]
x-content-filtered-by: Mailman/MimeDel 2.1.6
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

Hello Forrest,

I agree with you about the microcontrollers. Though, I can't change the
requirements.

Assuming that I can't find a smaller implementation (such as the analog
one) the XOR gates do look attractive.

On Friday, June 5, 2020, Forrest Christian (List Account) <
lists@packetflux.com> wrote:

> It's too bad that programmable devices are not permitted...   This is
> perfect for an edge trigger on a microcontroller, or a tiny programmable
> logic device.   I would argue that using the functions available on a
> modern programmable device is going to be at least as reliable as any
> discrete logic/component solution.
>
> But...
>
> Take four xor gates (1 single 74hc86) each wired as a 'edge to glitch'
> converter - that is, wire each line directly to one input pin and through=
 a
> rc filter to the other input pin.  This has the effect of slightly delayi=
ng
> the input to the second input pin, creating a situation where you get a
> brief pulse on the output on each edge as it catches up with the
> non-delayed first pin.
>
> You can then insert a diode into the output line, creating a 'wired or' f=
or
> the output, so if *any* of the units have an edge, you get a pulse.
>  Direction of diode and whether you need a pullup/pulldown resistor is le=
ft
> as an exercise to the reader.
>
> Once you have that pulse, feel free to use an HC123 or a 555 to stretch i=
t
> out.
>
> Or you could just try to convince whoever made the 'no programmable
> devices' policy that something like a PIC16F15313 which can be factory
> programmed by microchip is smaller, cheaper, and is just as reliable.
> Plus, it is highly likely that the entire function you describe can be do=
ne
> in one of the inbuilt "core independent peripherals" which wouldn't even
> require the core to be running, and the latency if done right wouldn't be
> any more than the discrete solution.  Or you can save a few cents if you
> can tolerate a bit of interrupt latency.  Of course, I can understand tha=
t
> sometimes in an application the 'black box' nature of a programmable devi=
ce
> isn't really possible to use.  But those applications are typically the
> type where you're going to have to qualify everything.
>
> On Thu, Jun 4, 2020 at 2:47 PM 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
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> - Forrest
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--=20
Jason White
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.