Serial communication and optocoupler
Faizal Rezi
I'm looking for optocoupler to protect my circuit from high voltage and
noise tha come from serial communication. I'm using MAX232 for transeiver
chip. Any recomendation what type of optocoupler I can use for?
Best regards,
Faizal Rezi
Jan Panteltje
<fai...@nettaxi.com> wrote in <ZyTL5.9788$K6.68008@news>:
In principle it is possible to put an optocoupler in the RS232.
However if your cables are any length, you can only use a low baudrate (say
300).
This because if the opto conducts, the cable is shorted (fast), but if it
opens, the cable capacitance is only charged by the rs232 current (slow).
Given this current and the cable capacitance you can calculate the rise time,
and from that the maximum baudrate you can use.
Regards
jan
Steven Ames
http://www.apisindustries.com/ai-232-a.html
Have a look at the family of logic-to-logic isolators from QT
Optoelectronics,
you can shove 10Mbits/sec through these little 6-pin devices.
http://www.qtopto.com/oi/o0501.htm
--Steven Ames
Jack Klein
wrote in comp.arch.embedded:
Agilent (still a division of Hewlett Packard?) makes optically
isolated 20mA current loop driver and receiver chips that I had a lot
of luck with in the past in some very nasty electrical environments
and to isolate some very high voltage differences. You use these
instead of, not along with, RS232 drivers and receivers.
Go to http://www.agilent.com/Top/English/index.html and type HCPL4100
in the quick search box if you are interested.
Jack Klein
--
Home: http://jackklein.home.att.net
Bruce
"Faizal Rezi" <fai...@nettaxi.com> wrote in message
news:ZyTL5.9788$K6.68008@news...
Hello Faizal,
Agilent Technologies has an excellent Design Guide to isolation
Circuits. Here is the URL for the guide:
http://www.semiconductor.agilent.com/isolator/design_guide.html
We have used several of the circuits in this guide with great
success, and they are very inexpensive to implement.
Regards,
Paul Keinanen
>Dear all,
>
>I'm looking for optocoupler to protect my circuit from high voltage and
>noise tha come from serial communication.
The most common problems with RS-232 links are ground loop currents
and thus, there is a difference in the signal ground potentials and
thus a reduced noise margin.
>I'm using MAX232 for transeiver
>chip. Any recomendation what type of optocoupler I can use for?
You should put the optocoupler between your logic and the RS-232
receivers/transmitters. Of course, you must use a separate floating
power supplies for the RS-232 receivers/drivers. In this way you can
avoid the ground loop currents and hence the noise problems associated
with it.
RS-232 connections should be avoided with long lines. A floating 20 mA
current loop is easy to implement with two optocouplers, especially if
you can configure your end as the passive side.
For very long distances and high speeds use optocouplers to run
floating RS-422 receivers/transmitters.
Paul
Faizal Rezi
I can use for. Because not all optocoupler can be used for this design.
Best regards,
Faizal Rezi
Ole Saether
We use the HCPL-501 (SO8 package) and 6N136 (8 pin DIP) for this.
Best Regards,
Ole Saether
"Faizal Rezi" <fai...@nettaxi.com> wrote in message
news:yqdM5.9852$K6.68883@news...