Not clear on the series clipper ... to be clear, you're suggesting the=20
zeners to drop the +/-10V RS232 signals to the 5-ish volt range then=20
feed that to the MAX3232, correct?... sort of like Dolby.

Cheers,
-Neil.


On 12/2/2014 12:39 PM, Dwayne Reid wrote:
> I'm coming to this thread late in the game, but I concur that
> translating to RS-232 levels may be your best bet.  Run as high a
> voltage as you can, then attenuate the signal at the receiving end so
> as to increase your noise immunity.
>
> MAX232 tops out at about plus minus 10V.  The original 1488 - 1489
> family can run at plus minus 25V.  But it's important to attenuate
> the signal coming into the receiver so that low-level noise is
> ignored.  Even better, use a pair of back-to-back zener diodes as a
> series clipper.  a pair of 5.6V zeners in series ought to do it - you
> are still well above the minimum input voltage at the receiver yet
> you can safely ignore noise impulses exceeding 5 or 6 volts.
>
> The advantage of using the MAX family or equivalent is, of course,
> that the bipolar power supply is generated right on the chip.
>
> dwayne
>
>
> At 08:36 AM 12/2/2014, Neil wrote:
>> I want to amplify some TTL-level signals for better noise immunity
>> through about 10'-15' of wire through a vehicle, and trying to figure
>> out what good options there are.  The data being transmitted is a custom
>> signal (not exactly async serial, and not exactly PWM) of approx
>> 50-100khz, at 5V.  Only one data-line out and one data-line back in.  It
>> works now, but noise issues we've experienced in other areas has me
>> worried, and the board is being revised currently, so I want to add this
>> also.  The wiring/harness is pretty much set in stone so I can't really
>> twist, shield or add wires for differential signaling, etc.  The
>> electronics at both sides of the line is pretty much all I can change.
>>
>> First thought is 74xx245's etc, but have the impression they're really
>> for strengthening signals for driving higher loads over short distances
>> (ie: still chip-to-chip comms).  The last time I used these was  a few
>> decades ago with a Z80 processor.  Not sure I should use it for long
>> wires across devices.  Another option is to use discrete transistor
>> push-pull drivers.  Also, I'm sure I can use a MAX3232 or similar for
>> this.  But are there any other better options?  Looking at digikey gives
>> me 10k+ options, and filtering by package, supply-voltage, cost, etc
>> still nets me a couple thousand options.  Favourite devices?
>>
>> Cheers,
>> -Neil
>

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