rs232 to rs232 isolator

[Electro nS]

i need to isolate rs232 signals coming from pc and going to a high power device rs232 serial port

I DONOT WANT LEVEL SHIFTERS (max232)

hopefully it will be compact and doesnot need external power source ?!! maybe ??
something like this : https://cnc-specialty-store.com/rs232-cables/rs232-optical-isolation-transceiver-protect-pc-isolator

find attached a diagram for better clarification


thanks in advance

 

[FvM]

For $11 I would give it a try.

 

[Electro nS]

its not the money , i donot want to order and wait for **INTERNATIONAL** shipping and such staff

do u think it is that hard ???

 

[schmitt trigger]

Use fast optocouplers like the FODM8061.
I've used them successfully all the way to 115Kbps

 

[Electro nS]

how should i connect the tx rx signals to the optocoupler , do you have the circuit u used ?

note : i am not using the rts cts pins , i am only using tx rx and gnd

 

[FvM]

You can't connect logic-level optocouplers directly to RS232 level, you need to use some kind of level translators, either IC or discrete circuits. O.K. there's an option of driving TxD with 0/5V level and hope the receiver will accept it. But that's not what I would do in the said industrial enviroment if noise immunity is an objective.

You also need to design a parasitic power supply utilizing TxD and possibly additional signals. If you buy the nice Chinese (or whatsoever) RS232 isolator, you get everything ready-made.

By the way, why do you say you don't use RTS/CTS pins? Using additional RS232 lines as auxilary power supply can considerably ease the isolator operation by providing a permanent positive voltage.

 

[hobbyckts]

You could use ACSL-6300 or ACSL-6400 from avago. I have tried using it in my design its working fine. You don't need any level shifters for it.

 

[FvM]

You don't need any level shifters for it.

So you are suggesting to drive RS232 with 0/5V logic level? Although this works with standard interfaces, e.g. of a PC, it's not guaranteed by RS232 spec.

The other point is, how are you supplying the optocouplers?

 

[Electro nS]

You can't connect logic-level optocouplers directly to RS232 level, you need to use some kind of level translators, either IC or discrete circuits. O.K. there's an option of driving TxD with 0/5V level and hope the receiver will accept it. But that's not what I would do in the said industrial enviroment if noise immunity is an objective.

You also need to design a parasitic power supply utilizing TxD and possibly additional signals. If you buy the nice Chinese (or whatsoever) RS232 isolator, you get everything ready-made.

By the way, why do you say you don't use RTS/CTS pins? Using additional RS232 lines as auxilary power supply can considerably ease the isolator operation by providing a permanent positive voltage.

wowwoo , i didnot know that i have to worry about all these details !! its easier if i incorporate in my original board an isolated rs232 transciver it would have been easier (but for new versions of the board) . i am thinking of buying 2 MAX250/1 pair and connect the logic side of these together , but i would be a huge circuit and a pain in the ass !

the reason for not using rts and cts pins is that i have never found anyone suggesting them over software handshaking
the micro controller interrupt on TX is enough right now although i am at 115200 rate . i wish i know the difference or advantage of hardware flow control (RTS and CTS) vs the software methods
could u explain the advantages or disadvantages mainly at high speed and large data transfer

thank u very much