RS232 Optical Isolation

Thread Starter

mohammad2050

Joined Nov 14, 2014
56
hi
i have a device that use RS232 Optical Isolation Transceiver for connect to pc . Now my question is : do it will work without Transceiver ?
 

cmartinez

Joined Jan 17, 2007
7,313
hi
i have a device that use RS232 Optical Isolation Transceiver for connect to pc . Now my question is : do it will work without Transceiver ?
I don't understand your question. There ARE optically isolated RS232 transceivers out there, and their intention is to protect the equipment. But you need TWO transceivers to make an information transaction on RS232, whether they're optically isolated or not...
 

Papabravo

Joined Feb 24, 2006
15,794
because this Transceiver is for protect between pc and device , Both sides is RS232
Then I don't understand what you are asking. Do you want to remove the isolation and replace it with wires?
If so you may get quite a surprise when you connect signals with different voltage levels together. The isolation is there for a reason, unless you think it isn't. You might as well give us a schematic so we can tell what you are talking about.
 

Papabravo

Joined Feb 24, 2006
15,794
RS-232 is often implemented with different voltage levels. The spec says a MARK is any voltage in the range [-3V..-25V] with respect to GND, and a SPACE is in the range [3V..25V] with respect to GND. A voltage in the range [-3V..3V] represents an undefined signal. It is neither a MARK or a SPACE. The purpose of the isolation is that you have signals generated from different power supplies that do not share a common ground. In fact the grounds might have several hundred volts difference between them. Do you really want to connect the two devices together if this is the case? Only someone who didn't know what they were doing would try to do this.
 

Thread Starter

mohammad2050

Joined Nov 14, 2014
56
OK , thank you Papabravo for well information
Now I have another question :
still can not be done , If be close together two power supply?
for example : power supply is 10 volt in devise side and other side is my laptop (use usb to RS232 converter) . Is it still can not be done ؟
 

Papabravo

Joined Feb 24, 2006
15,794
OK , thank you Papabravo for well information
Now I have another question :
still can not be done , If be close together two power supply?
for example : power supply is 10 volt in devise side and other side is my laptop (use usb to RS232 converter) . Is it still can not be done ؟
It depends. Do you know what levels the PC is using from the USB to RS232 converter.
 

MikeML

Joined Oct 2, 2009
5,444
The optical isolation for a RS232 link is not because there are different voltage levels in the signals; it is because there is likely a potential difference between the ground potential on the remote equipment chassis and the ground potential on the PC chassis. If you connect the RS232 cable without optical isolation, you create a "ground loop" between the two devices, which will screw up the signals...

It can also be done for safety. If the remote equipment is for swimming pools, spas, medical devices, etc., then there could be a shock hazard that comes from the PC power supply along the common wire in a non-opto-isolated RS232 cable. The opto-isolation effectively lets the remote equipment operate at a different ground potential than the PC.

If the maker of the remote equipment wants opto-isolation, it is for a reason, and you would be a fool to eliminate it...
 

Papabravo

Joined Feb 24, 2006
15,794
The optical isolation for a RS232 link is not because there are different voltage levels in the signals; it is because there is likely a potential difference between the ground potential on the remote equipment chassis and the ground potential on the PC chassis. If you connect the RS232 cable without optical isolation, you create a "ground loop" between the two devices, which will screw up the signals...

It can also be done for safety. If the remote equipment is for swimming pools, spas, medical devices, etc., then there could be a shock hazard that comes from the PC power supply along the common wire in a non-opto-isolated RS232 cable. The opto-isolation effectively lets the remote equipment operate at a different ground potential than the PC.

If the maker of the remote equipment wants opto-isolation, it is for a reason, and you would be a fool to eliminate it...
I did make the ground potential argument in post #7. That said if we are talking about a laptop and another device that sits on the desktop there may not be much potential difference between the grounds. It would be helpful to know more about the TS/OPs device.
 
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