Well, Mike, maybe we can adjust some
of those operational parameters.

>  1. Wider input gap.

How wide? 0 - 50V

How about using a simple resistive divider in
conjunction with the input interal resistance
of the line receiver?

Or - how about a resistive divider in front of
a CMOS 74C14 Schmitt Trigger hex inverter?

You could set your 'trigger' range AND have static
protection plus direct interface to 5V logic on
the output ...

>  2. Higher bottom threshold.

A divider network would give you this ...

>  3. Lower input impedance.

EASY to do - add external R's as req'd to lower
the Z (the 'impedance') ...

>  4. Ability to work from open collector source.

In any case - you would need a "pull-up" to some
voltage here ...

>  5. Some flexibility to cope with other requirements.

Like? (I didn't follow previous follow-ups to this
topic so I might be going over some questions that
have been asked already.)

Some of the airborne mil gear that I have worked on
in the past used actual "voltage comparators" as
the active interface device between the outside
world (where transients and RF can abound) and
the internal world of "protected" 5V TTL logic
around the bit-slice processor.

This was on the Panavia Tornado Nose-mounted RADAR
aboard the tri-country produced all-weather
bomb-delivery aircraft known as the Panavia
"Tornado" bomber designed originally for use
in the European theater as an "all weather
bomber RADAR-guided weapons delivery platform"
for use against the perceived 'Red Threat' (or
'Red Menace' <grin>) in previous decades ...

Switch inputs from the cockpit to the LRU 1 (Line
Replaceable Unit #1), the 'processor/computer'
were 'buffered' via these circuits using voltage
comparators (like the uA711, bascially op-amps
but with no particular emphasis on linearity and
logic-driving outputs) and protective capacitor
and resistor networks ...

RF Jim

----- Original Message -----
From: "Mike Singer" <mike@POLUOSTROV.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, October 18, 2002 10:31 PM
Subject: Re: [EE]: Foolproof input line


> Thank you, Jim.
>
> I'll keep them in my mind. But from the first glance:
>  I need:
>  1. Wider input gap.
>  2. Higher bottom threshold.
>  3. Lower input impedance.
>  4. Ability to work from open collector source.
>  5. Some flexibility to cope with other requirements.
>
>  Mike.
>
> Jim wrote:
> > Mike, have you considered simply using something
> > from the MC1489, MC14C89, SN75189, SN75C189,
> > DS1489, and DS14C89 family RS232 line receiver
> > family?
> >
> > This chip series is basically billed as a:
> >
> >   "ESD-Protected, Quad, Low-Power RS-232
> >    Line Receiver"
> >
> > but will work to 'detect' TTL  and CMOS logic
> > levels *and* is protected for electro-static
> > discharge ...
> >
> > Brief specs:
> >
> >  Input low:     approx. 1 V
> >  Input high:    approx. 2 V
> >  Working range: +- 25V
> >  Approx Rin:    5 KOhms
>
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