Hi Rafael
        We do it all the time depends on the currente and voltage required.
as the voltage used is the same you just have to watch the max currente
allowed in the opto-isolator.
hope it helps
        best regards
                        Luis

-----Original Message-----
From: Rafael Vidal Aroca [mailto:rva@GRAD.ICMC.USP.BR]
Sent: 09 January 2004 23:44
To: PICLIST@mitvma.mit.edu
Subject: [EE]: Relay & Opto Coupler & Transistor


        Hi guys, there is a question i'm always in doubt. Let see if anyone
can
make it clearer.

        I always followed the traditional rules as the diagram below taken
from
http://www.hut.fi/Misc/Electronics/circuits/parallel_output.html

                                                   V+  (12V)
                                                  |
                                     +------------+
                                     |            +------+
Parallel                            |            |      |
Port                                |    D1     ---     |
                                     |   1N4001  / \    Relay coil
           R1    1  ----------- 5    |          /---\    |
  D(x) ----1k------| Opto-     |-----+            |      |
                   | Isolator  |                  +------+
  GND -------------|           |-+                |
                 2  ----------- 4|                |
                    CNY 17 or    |   R2        | /
                    4N25         |   4.7K    B |/  C   T1
                                 +--\/\/\/\/---|      BC547A or 2N2222A
                                               |\  E
                                               | V
                                                 |
                                           external circuit ground

        But i already saw, and assembled myself a circuit without the
transistor, with the 4N25 being connected directly to the relay and the
diode. Is it right or wrong? What are the implications as both seem to
work well.

        Thanks.

[]s Rafael.

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