[time-nuts] RS 232
EWKehren at aol.com
EWKehren at aol.com
Thu Jul 25 23:05:12 UTC 2013
on some of my projects some prefer to use RS 232 and I am not arrogant
enough to say that RS 232 is not an option but try to help them and that was
why I asked the original question to make it for them as simple as possible.
I combine opto with USB but if you want to run 10 devices at the same time
as one time nut asked me about no one I asked had an answer.
Bert Kehren
In a message dated 7/25/2013 5:48:16 P.M. Eastern Daylight Time,
john at miles.io writes:
Agreed, nobody should be using RS232 for anything nowadays. USB doesn't
seem to cause noise problems in equipment that works at the -170 dBc/Hz
and
below level (ahem) so it will be good enough for most other sensitive
applications, assuming good design/layout practices are followed.
USB support chip manufacturers have a lot of experience supporting
customers
who need their USB devices to pass FCC, CE, and other worldwide EMI
standards. There are a lot of good app notes and other literature out
there. As far as what components to use, I'd suggest checking out
www.ftdichip.com if you're looking for the proverbial "path of least
resistance." You can't get much simpler than an FTD232B.
-- john, KE5FX
Miles Design LLC
> -----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, July 25, 2013 12:32 PM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] RS 232
>
> 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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