Is optical isolation required for parallel port applications ??

[arunb]

Hi,

Is optical isolation required for parallel port applications, the application will be powered externally from a 230 V ac source..

thanks
ar

 

[Papabravo]

Required? - No
Adviseable? - maybe
You need to give more details on what you have in mind.

 

[mneary]

Sorry, you need to tell more about the 230 Vac device.

You definitely need to separate the PC common from any mains. If the device contains its own transformer and earth connection, then it's probably permissible to connect directly from one system's logic to the other.

If the device does not have its own isolation from the mains then optical coupling is necessary but possibly not sufficient.

 

[Gayan Soyza]

When dealing with computer PORTS I always use OPTO ISOLATORS.
Even for small LED bulbs to turn ON and OFF.

To drive RELAYS for large handling current application’s I take the OPTO COUPLER OUTPUT through a TRANSISTOR to a RELAY.

 

[arunb]

The device will contain a 230V/18 V AC step down transformer. The voltage will be rectifed and regulated to 5 V DC using a 7805 regulator IC.

thanks
ar

 

[ericgibbs]

The device will contain a 230V/18 V AC step down transformer. The voltage will be rectifed and regulated to 5 V DC using a 7805 regulator IC.

thanks
ar

IF all the signals in and out of the Port at TTL logic levels, that is, 0V to +5V, as you are using an isolation transformer with a regulator, no opto-isolators are required.

IF the logic/devices that you have connected are switching mains or high voltage devices then opto-isolators should be used.

What are you planning to control with the port???

 

[philba]

this issue isn't completely about what is being controlled. There are many sources of ESD (or worse). The farther the device is from the computer, the more likely something nasty will find it's way down the wire. Just walking around on a low humidity day can build up a huge static charge. use isolation as a mater of good, defensive design.

 

[ericgibbs]

this issue isn't completely about what is being controlled. There are many sources of ESD (or worse). The farther the device is from the computer, the more likely something nasty will find it's way down the wire. Just walking around on a low humidity day can build up a huge static charge. use isolation as a mater of good, defensive design.

hi,
I am more concerned about the OP's personal safety, regarding operating mains powered devices from the port.

Good engineering practice requires adequate ESD protection as matter of basic design.

Regards

 

[philba]

hi,
I am more concerned about the OP's personal safety, regarding operating mains powered devices from the port.
...
Regards

I can't disagree but thought the discussion was about the need for isolation. While isolation may provide some protection to a user, it's main purpose is to prevent damage to electronic devices. GFIs, fuses, breakers and proper wiring are more important for life safety.

 

[ericgibbs]

I can't disagree but thought the discussion was about the need for isolation. While isolation may provide some protection to a user, it's main purpose is to prevent damage to electronic devices. GFIs, fuses, breakers and proper wiring are more important for life safety.

Extract from an OP's post.
The device will contain a 230V/18 V AC step down transformer. The voltage will be rectifed and regulated to 5 V DC using a 7805 regulator IC.

I see that we agree in principle, but as the OP's posts are not clear in how these devices will be connected,
I would prefer to err on the side of caution with my replies.

IMO the use of isolation is to protect users, GFI's and proper wiring are essential, but fuses or breakers will not protect a user,
they will protect the equipment.

 

[philba]

Then, we disagree. I won't take the argument farther, though.

 

[ikalogic]

sometimes a simple buffer can do the job