Hi Bert,
My attitude is if you are going to provide an RS-232 port then do it
properly (min of +/- 3 volts & max of +/- 25 volts). RS-232 is still a
popular item in the hobby controller world, although USB is gaining
ground. In so far as stability goes, RS-232 is much cleaner and easier
to handle in the micro coding compared to USB. With that said, there is
nothing wrong with providing both, it just makes the coding a bit
harder. If you need long lines and want common mode suppression then
utilize RS-485, a derivative of RS-232.
You could also use TOSLINK, the fiber optic lines used in the audio
field. The components are fairly cheap compared to other forms of
plastic or glass (more expensive) fiber products. Most products will
handle up to 5 MHz at reasonable distances. If you are careful in
selecting the TX and RX port parts it can go up to 15 MHz at the top
end, especially at short distances.
Irrespective of all that, the power source has no relationship to the
RS-232 or USB for that matter.
73....Bill....WB6BNQ
ewkeh...@aol.com wrote:
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,
ma...@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-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of ewkeh...@aol.com
Sent: Thursday, 25 July 2013 11:39 PM
To: time-nuts@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
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
