Schematic for using an optoisolator

Hey Everybody

I am looking for a ac input optoisolator circuit. I am using this for an input to a 12vdc operated PLC. I need to be able to detect the presents of a ac input. This will then allow the Plc to perform
the logic depending the presents of the voltage. I am using a NTE3089
and really have no idea how to configure the output. I have a 27k resistor to the input of the device to drop the voltage from 120vac to about 60vac. Can anyone help?

Thanks
Lionel

Sinking or sourcing input?...

A more inportant question that I have...

How do you plan to mount this????? Sorry, but I'm not a big fan of the "home brew" method. Using an IC might be good for learning, but not good in an industrial environment.

Have a look at something like THIS. A G4IAC15 in a socket will be simple to wire, with many less headaches in the future.

Hey, wait a minute... Is there a reason why you can't just use a 120VAC relay?...

Cheap and easy... Can't get much simpler than that...

beerchug

-Eric

Optoisolator

Eric

This device will be in a good inviroment (motorhome).I would rather use electronic devices instead of relays. Once I get it designed then I will worry about it looking home made. Different monitoring devices use this theory. I just can't find any schematics on this type circuit.

Lionel

If you are really into kludging, then a resistor and diode may be all that's required.

Most PLC 12VDC input circuits already employ an opto coupler, and if this is the case then you may get away with simply adding an external resistor to ensure current is limited to the original spec, plus add a diode to prevent reversal of polarity. Obviously it's going to be easier if you have a schematic of the PLC's input circuit, but 10k resistor and IN4004 would likely be in the ballpark. The resultant signal will now be 1/2 wave and would require some filtering, but often this is already dealt with on the 5V side of the coupler. Worst case just add 10 mf or so to filter things out.

Don't recommend trying this unless you clearly understand the existing circuit and the effects these additions will have. A floating DC supply won't do here as you'll need a reference to the AC side.

I'd just buy a relay myself.........

Hey Lionel,
How about a compromise and just use a solid state relay. Crydom sells
a PhotoMOS which looks to be a "OPTO relay" in a IC package you might want to have a look. Here is the link to it "Crydom PhotoMOS"