[time-nuts] RS 232
EWKehren at aol.com
EWKehren at aol.com
Thu Jul 25 20:34:23 UTC 2013
Bill
Thank you I am only looking for a solution that is simple in Corby's case
we used a separate power source, but the question is, is it necessary. That
is why I brought it up to the list. Shopping for ideas.
Bert
In a message dated 7/25/2013 4:06:03 P.M. Eastern Daylight Time,
wb6bnq at cox.net writes:
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
EWKehren at 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,
>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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