Exactly. The idea is to eliminate noise spikes by subtracting from=20 the input signal. dwayne At 11:05 AM 12/2/2014, Neil wrote: >Not clear on the series clipper ... to be clear, you're suggesting the >zeners to drop the +/-10V RS232 signals to the 5-ish volt range then >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 cust= om > >> 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 th= is > >> also. The wiring/harness is pretty much set in stone so I can't reall= y > >> 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 distance= s > >> (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 giv= es > >> me 10k+ options, and filtering by package, supply-voltage, cost, etc > >> still nets me a couple thousand options. Favourite devices? > >> > >> Cheers, > >> -Neil > > > >-- >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 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=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 .