Isolation for RS232 signals (RXD, TXD, GND) ?

Thread Starter

Kumaraguru

Joined Jul 15, 2020
5
Is this to use RS232 levels in and out, or logic levels to RS232 levels?
Hi AlbertHall, Thank you for quick response. We have two equipment's which are connected by RS-232 ports for communication. The ports on eqipment's contain three signals (TXD,RXD,GND). For this we require isolation (5kVrms). The interface device designed shall be plugged between the equipments. The RS232 device is bus powered. no external supply to be used.
 

andrewmm

Joined Feb 25, 2011
532
Interesting,
I wonder where you get the power from to drive an isolator, if you have no power ?
do you rely upon pull ups at the receiver to supply sufficient current for an opto isolator to work ?
 

Thread Starter

Kumaraguru

Joined Jul 15, 2020
5
Interesting,
I wonder where you get the power from to drive an isolator, if you have no power ?
do you rely upon pull ups at the receiver to supply sufficient current for an opto isolator to work ?
No external power option is available. Since both E2E equipment only have three wire. The Commfront RS232 is just a three wire isolator. I am searching for similar design to be implemented.
 

andrewmm

Joined Feb 25, 2011
532
As was mentioned by @AlbetHal in https://www.epanorama.net/circuits/rspower.html

You "can" get "some" power of the DTr / DTS lines , but you dont have them.

Also mentioned is that you "can" get power off the signal lines,
I've been involved in such a long time ago,

But we ran into the problem mentioned in the link, "modern" computers don't drive +- 12 v as per the original RS232 spec.
"modern" , if you can call a computer with a D connector modern, is RS232 D or E I think , which tends to be 5v if your lucky, more like 3v3 if your not luck, and 0v.

Not enough power to use .
Our application , we we lucky , in that we could depend upon there being a long pause between bursts of signals, enough to charge up the PSU to drive the uP when needed.

It depends upon your system, you might be able to get away with simple passive opto isolator and a transistor and rely upon pull up at the receiver and sender ends.
 
Top