🚀 go-pugleaf

In article <MZb4w2600WB88M=4wv@andrew.cmu.edu> kg19+@andrew.cmu.edu (Kurt A. Geisel) writes:
>I am trying to convert a TTL signal into an RS-232 signal.
...
>When the TTL input is at 0 V, the RS-232 output is at 3.25 V.  When
>the TTL input is at +5 V, the RS-232 output is at 3.94 V.  Needless to
>say, this is useless.

I would recommend supplying the 1488 with +/- 10 Volts minimum, +/- 12 is
better.  RS-232 with output swings less than +/- 7 Volts will have problems
driving all manufacturer's receiver chips at high baud rates over
longish lines.  The spec says the length should be < 50 feet, I'm not sure
what kind of wire and max baud rates are within spec.

I am guessing that your system only has 5V supplies, and putting in a +/-
12 V supply is kind of expensive for just a little RS-232 driver.
Maxim and Intersil (and others?) make some really great RS-232 driver/receiver
chips that have built in charge pumps so that you can get +/- 10V signals
using only a 5V supply.  The original chips from Maxim had some problems,
but I have had no problems with recent batches.

 ^   ^  Forrest Cook - Beware of programmers who carry screwdrivers - LB
/|\ /|\ cook@stout.ucar.edu (The preceeding was all my OPINION)
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