Circuit for opto isolated rs232

PaulF

Hi all,
can anyone point me to a suitable circuit for implementing optically isolated rs232 via max 3232 and the propeller. I have searched the web and found bits of a circuit here and there, but I'm sure some 'prophead' has done this before. I have also read somewhere (I believe on this forum) that opto isolators are not fast enough for comms (I hope to run at speeds of upto 115,200 bps), is this true.

Paul

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"There are 10 types of people in the world. Those who understand binary and those who don't."

Post Edited (PaulF) : 6/29/2009 9:58:03 PM GMT

pjv

Paul;

Use the ADuM 5400 series (think that's the number) series chip. Gives isolation, high speed data and some small amount of power accross the barrier to boot.

I use them and they work great... slightly costly, but manageable.

Cheers,

Peter (pjv)

Nick Mueller

Attached a cutout of a schematic that actually runs at 115kBaud.
Note the DC/DC-covnerter in the upper left.

There are alternatives for the OCs, MAX and DC/DC-converter! Have a look at Analog for their ADM3251E. It absolutely is an alternative. Less footprint, less overall cost. But maybe hard to get. ) Haven't tried it yet, but next time for sure (and Analog makes no BS).


Edit:
Oh! And I got the numbers wrong for the D-sub9.

Edit 2:
Not so sure wether I corrected it in the schematics. R3.1 and R3.2 might have to be 3k9.


Nick
Note to myself: Nick, finally get the chips out of your keyboard! So many missing characters. Will do that right now ...

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YADRO

Post Edited (Nick Mueller) : 6/29/2009 10:43:33 PM GMT

PaulF

@Nick - Thanks , the 3251E certainly seems to be the business regarding component count. I'll try to get my hands on some of these.
@Peter - Can't find anything on the ADuM 5400 series, perhaps you meant the same as Nick?

Anyway, its late here and time for me to hit the sack. Will research further tomorrw. Thanks again.
Paul

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"There are 10 types of people in the world. Those who understand binary and those who don't."

waldillo

Hi friends:
I´m trying to develop a circuit RS232 opto isolated.I´m trying to atached some RS232 device to the pc and i want not to destroy the PC serial port.
Anyone has the complete circuit? I would be so glad of get it. Thks

Could i get the power from the PC?

Phil Pilgrim (PhiPi)

Here's a post/thread that may help:

http://forums.parallax.com/showthread.php?p=677116

-Phil

kwinn

rs232 to optoisolator to rs232 is a bit redundant. The 3.3V (or 5V) data signals could go to/from the optoisolators directly as current loop.

Peter Jakacki

I use the ADUM5402 in a commercial design although there are quite a few digital isolators available these days. The main advantage over optos is that they are:

1) High Speed 1M...25Mbps typical
2) On-chip generation of isolated supply - selectable as 3.3 or 5
3) All in one package, no coils or transformers required, just the caps.

BTW, you can use optos for high-speed but they can't be your garden variety types. For RS232 I would have used something like a HCPL2531. But that would require two optos and a DC-DC converter. Definitely go the digital isolator route.