For short cable and non-critical use, CMOS levels (0-5V) work fine.
RS-232 receiver thresholds are actually similar to TTL levels
(0.8-2.7V), though the spec is for +/-3V minimum drive for noise
immunity. Phantom power can be gotten from the control lines - this is
how serial mice are powered.
David
On 7/25/13 10:21 AM, paul swed wrote:
Debating the band belive ideal for older is +-3V. But I would need to
check. And how old is old? Not to sure many of the old 1488 1489 devices
are around anymore.
I think more compatibility would be supported by the +-1.4 you mention.
Regards
Paul
WB8TSL
On Thu, Jul 25, 2013 at 9:39 AM, <[email protected]> wrote:
Since joining time nuts over four years ago I have not used a single MAX
232 chip. Two reasons MAX do not give me isolation and do generate noise
in
critical applications. I prefer the use of two H11 opto couplers which
work
perfect. On the receiving end the diode along with a current limiter and
blocking diode for the negative level works perfect. On the output side a
power source is needed. If one uses an USB adapter it does have the + 5
volt
which again works perfect. How ever many prefer to use RS 232 direct and
that is why I hope to get some comments and suggestions from the list.
Corby
used on our counter circuit that he described a separate power source.
Present MAX circuits use a + 1.4 volt threshold but considering legacy the
question is what should the voltage swing be to make it compatible for
most PC's and what options exist to get the necessary voltage. In the past
other pins on the RS 232 port where an ideal power source. Still an
option?
Bert Kehren
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