Decades ago, I resolve this with current drive, 20mA for logical one, at=20
56kbauds (very fast for the epoch) in a line 100m, or more, long.

Vinicius



On 02-12-2014 16:07, Neil wrote:
> I have not, but I did coincidentally spend the last 15 minutes looking
> up termination resistors.  Everything points to RS232 and RS485 though,
> so I want to find a good intro to how to calculate the ideal termination
> resistor value for my individual-conductors system.
>
> Cheers,
> -Neil.
>
>
>
> On 12/2/2014 12:44 PM, Bob Blick wrote:
>> Hi Neil,
>>
>> Have you tried adding a load resistor to the receiving end? If you are
>> driving the line with a PIC you can use 220 ohms and that will scare
>> away most noise.
>>
>> Cheerful regards, Bob
>>
>> On Tue, Dec 2, 2014, at 07:36 AM, 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 custo=
m
>>> 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.  I=
t
>>> 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 thi=
s
>>> 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 give=
s
>>> me 10k+ options, and filtering by package, supply-voltage, cost, etc
>>> still nets me a couple thousand options.  Favourite devices?
>>>
>>> Cheers,
>>> -Neil

--=20
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