Double check 2? - Electronic Circuits Projects Diagrams Free

hjl4 · 23rd August 2005, 02:13 AM

Ok, I know, my first post was sort of incomplete.

So I revised it a bit to see if anyone, as to get another opinion, can go over the schematic, and see if anything is wrong with it.

I build my own electronic circuits ect.. and program microchips, but this is my first
time trying to isolate the parallel port of a PC, with opto electronics.

I just need someone to confirm that everything is OK, before I purchase the parts for this.

The inputs are low voltage and only require resistors to isolate.
The outputs, are to control relays ect... and need to be isolated.

In this schematic, you'll quickly see which is which.
Thanks in advance. My first post had no replies, which leads me to beleive, no one is interested.

Roff · 23rd August 2005, 02:52 AM

You thought no one was interested. You need to consider another possibility. Maybe everyone was waiting for someone else to answer. That's what I was doing. I am no parallel port expert. I can tell you what I can deduce from what you have presented.
You gave no resistor values, so I'm assuming you know what the current transfer ratio of the TIL193 is, and how to calculate the input current - including what the current drive capability of the parallel port is.
The outputs will rise to about 11.3 volts when you put a logic high on a port pin, assuming you don't have the emitter loaded too heavily. You will generally need some sort of pulldown resistor on each emitter if you want to guarantee that the emitter will return to 0V in a timely fashion. The emitters will probably not drive relays directly. Most relays require more current than the emitters can provide.
I can't comment on your inputs.

hjl4 · 23rd August 2005, 03:30 AM

Thanks Ron H,

for at least replying to this post. For a moment there, I thought this was too much to ask. I'm on a dead line, and this is but a small fraction of the total project.

I am aware of the necessary resistors required, and mostly needed confirmation on the general principal of opto isolation.

As for the three relays, the optos will trigger, amplifing NPN transistors, which in turn will energize the relays ect...

Again thanks for stepping out.

Now I can move on.

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23rd August 2005, 02:52 AM	(permalink)
Roff	You thought no one was interested. You need to consider another possibility. Maybe everyone was waiting for someone else to answer. That's what I was doing. I am no parallel port expert. I can tell you what I can deduce from what you have presented. You gave no resistor values, so I'm assuming you know what the current transfer ratio of the TIL193 is, and how to calculate the input current - including what the current drive capability of the parallel port is. The outputs will rise to about 11.3 volts when you put a logic high on a port pin, assuming you don't have the emitter loaded too heavily. You will generally need some sort of pulldown resistor on each emitter if you want to guarantee that the emitter will return to 0V in a timely fashion. The emitters will probably not drive relays directly. Most relays require more current than the emitters can provide. I can't comment on your inputs. __________________ Ron (aka Rube)

23rd August 2005, 03:30 AM	(permalink)
hjl4	Thanks Ron H, for at least replying to this post. For a moment there, I thought this was too much to ask. I'm on a dead line, and this is but a small fraction of the total project. I am aware of the necessary resistors required, and mostly needed confirmation on the general principal of opto isolation. As for the three relays, the optos will trigger, amplifing NPN transistors, which in turn will energize the relays ect... Again thanks for stepping out. Now I can move on.