[time-nuts] RS 232
EWKehren at aol.com
EWKehren at aol.com
Thu Jul 25 20:52:54 UTC 2013
Thank you Paul. This is exactly what I wanted to know, as I said I already
use the opto couplers the only thing is where to get the power from for the
transmitting side and you answered that. I will not use it but some others
may. I will stay with opto USB..
In a message dated 7/25/2013 4:40:24 P.M. Eastern Daylight Time,
paulswedb at gmail.com writes:
Bert
I will add back in here. The max232 has the internal switching oscillator
and that makes the noise. But you know that. So an external +/-supply
linear is cheap and simple. Full wave bridge and 2 caps. No regulation
needed. Using your opto isolator provides complete noise and electrical
isolation. Computers are nasty beasts especially when you grab +/- power
from the rs232 port. Some one re-confirmed my thinking that the rs 232 spec
was +/-3V for noise margin. I think thats about all there is.
Sorry if I am misunderstanding your need.
Regards
Paul
WB8TSL
On Thu, Jul 25, 2013 at 4:34 PM, <EWKehren at aol.com> wrote:
> 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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