[time-nuts] RS 232
EWKehren at aol.com
EWKehren at aol.com
Thu Jul 25 19:32:20 UTC 2013
I do not understand your question, I am referring to low noise applications
like counters for dual mixers or other AV measurements, but also Shera and
even Tbolt where external noise should be kept to a minimum. When you
chase 1 E-14, isolation is key and I always like to err on the cautious side
and as I stated we use blue tooth or USB but in the case of USB there are
always H11 in the circuit. Some still like to use RS 232 and the subject came
up and I have on my boards H11's like on the counter Corby uses but he
ended up using an external power source and I like to eliminate that
requirement. David had the right answer using the power that the RS 232 mouse uses
out of a DB 9, started looking but I do not have one any more and I can not
find any data.
Bert
In a message dated 7/25/2013 2:48:43 P.M. Eastern Daylight Time,
marks at non-stop.com.au writes:
Hi Bert,
I am sure your circuit is clear in your head, but would you mind attaching
detail?
You have perked my interest with the "low-noise" keyword ;)
-marki
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of EWKehren at aol.com
Sent: Thursday, 25 July 2013 11:39 PM
To: time-nuts at febo.com
Subject: [time-nuts] RS 232
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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