I'm trying to figure out how to use this simple isocoupler in a circuit, to protect my pc board, through my parallel port and I can't get the led side to have any effect on the transistor side.

the led suppose to satureate the base, and feed current through the transistor, completing the circuit. I'm building a motion control device, with a stepper motor, and I cant seem to get past the simplest part. Any help is greatly appreciated. the part is [link].
I'm using a 12v power supply I rigged up from an old pc.

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=41013&productId=41013&keyCode=PDF[/link]

Thanks to anyone!

7/27/2009 8:27:17 PM

I don't understand a single word in this thread. Hopefully someone else will.

Welcome to tdub

7/27/2009 8:44:18 PM

hmmmm, lets try this. Does any one know what a transistor is, and how its works. take it slow....

7/27/2009 9:05:38 PM

English, holmes... we are not all computer wizzes.

7/27/2009 9:08:46 PM

How do you have things wired and how are you checking that it isn't working?

That is, do you have it hooked up to your parallel port now? Do you at least have a multimeter, preferably an o-scope?

[Edited on July 27, 2009 at 9:10 PM. Reason : .]

7/27/2009 9:09:12 PM

Are you sure you're biasing the diode properly? With enough current?

7/27/2009 9:40:19 PM

oh god

7/27/2009 9:44:16 PM

What ^^ & ^^^ said, plus

1) Jameco is a sleazy fucking company. Have you verified the part you have is the correct part and that it actually works?

2) Have you thought out and drawn your circuit on a piece of paper (as opposed to just soldering a bunch of wires together)?

3) Have you breadboarded the opto-coupler in a simple circuit (i.e. simple drive circuit--not the parallel port, simple driven circuit) to verify things work like you think they do?

4) Are you sure the parallel port is capable of driving the optoisolator?

5) Watch frequency response of the optoisolator. It may be worth your effort to use a test circuit to see how the optoisolator behaves over a range of frequencies.

7/27/2009 9:48:07 PM

You can look in the data sheet for the last one, it has a ton/toff time of 4 and 3 microseconds. Anything faster than that and the transistor won't fully switch. I don't know a ton about stepper circuits but I don't imagine anyone using a 250khz signal to do the work.

7/27/2009 9:55:59 PM

I have portable test equipment and can help you next Tuesday if you can't get it to work by then.

7/28/2009 7:19:01 AM

fail boat... hilarious.
So i don't have an o scope but I have everything else. it is on a bread board, and I can make the transistor side function,....properly? the led seems to function, let current only one way...

I know it can be driven by a parallel port, this particular opto was used in a similar situation.
I'm just using the 3.xV on the led side of my getto ass pc PS to turn on the LED, while I am experimenting with the B E C on the transistor side, with a load. It's not even on the Port yet. I want to protect my computer, ya' know? I just need to know WHERE to hook up my circuit to.
Ground to load, to emitter, then 12V to Base? i'm obviously doing something wrong.

Jameco Sucks? is there anyplace on the Ecoast that you can have a good selection, and not by in multipules of 1000?

7/28/2009 7:29:42 PM

Buying from Jameco is like buying from the flea market. It's not the worst thing in the world, but you have to be careful. They're not afraid to substitute.

Quote :

"I just need to know WHERE to hook up my circuit to. Ground to load, to emitter, then 12V to Base?"

Based on this, I question whether you really know how transistors or opto-isolators work.

Leave the base floating. Connect the load either

12V -> load -> collector; emitter -> ground

or

12V -> collector; emitter -> load -> ground

I'd recommend you experiment some to learn how opto-isolators and transistors work. Use a resistor for the load and vary current through the diode using a potentiometer.

Pay attention to CE current and voltage, and see how they vary with diode current. Transistors and opto-isolators are current controllerd devices; you can see how CE current varies with diode current.

You can also do similar things with a transistor to see how CE current varies with base current.

[Edited on July 28, 2009 at 10:05 PM. Reason : ]

7/28/2009 10:03:43 PM

draw the circuit. ill fix it.

7/28/2009 10:26:47 PM

there's nothing wrong with Jameco. company i used ot work for sourced a lot of parts from them... we didnt have any more supplier failures with them than with anyone else.

7/29/2009 2:44:28 AM

anyhow, it's very likely you've fried your part, hooking it up all Willy Nilly to a "rigged" computer 12V DC supply.

so the first thing you need to do is breadboard this part to make sure it works.

use a 100 ohm resistor in series with the diode and trigger a 5V pulse using a function generator through the diode.

use a 2K resistor on the transistor source, connect emitter to ground, leave base NC. apply a 5V regulated power supply to teh resistor feeding the transistor source. measure the emitter-follower pulse with a scope at the source pin referenced to ground.

verify the part still works before continuing.

then verify that you actually get a signal that toggles from the parallel port pin, like you think it does.

use the parallel port to transmit to your diode side of the optocoupler, just like the breadboard example, including a 50 or 100 ohm resistor.

if you're going to use a 12V DC supply youll need a relatively higher resistance for the source, depending on how much current the transistor can sink.





[Edited on July 29, 2009 at 3:03 AM. Reason : ]

7/29/2009 3:01:51 AM

I had no idea he was working with a hybrid bjt/fet. That's kinda cool.

7/29/2009 8:08:20 AM

Must be fixed! Too lazy to draw in paint for 10 minutes. A++++

7/29/2009 12:28:10 PM