Re: Semi OT: Using an optocoupler in a switch matrix

On Feb 10, 11:42 am, kenny_ii <kenny_...@xxxxxxxxx> wrote:
4N25 is very similar to 4N35, the 4N3x family has different CTR's
depending on the circuit.   What is interesting is they both have a
very low reverse voltage breakdown threshold, 7 volts or lower.  If
you have is connected backwards to a source more than that, it may
break down.  Also, are you leaving pin 6 floating?  That acts as an
input to the base of the opto transistor.

I've done quite a bit with slow signal opto isolators for my job, let
me know if I can help out.

You may also find this page on opto isolators useful:http://homepages.which.net/~paul.hills/SpeedControl/Optos.html

K2

On Feb 10, 11:52 am, lruper...@xxxxxxxxx wrote:



Thanks for the reply. I thought it was very odd myself. I considered
that I might have the polarity reversed but even then I would have
expected no switch closure at all rather than an what appears as a
dead short through the transistor.

The system that I'm interfacing with is Bally 6803.

I took a look at the schematic for the mod you made and that's
basically exactly what I'm trying to accomplish. I think I'll try a
4N25 tonight and see how that works out.

Thanks again.

On Feb 10, 10:45 am, beaver <e...@xxxxxxxxxxxx> wrote:

Very odd.  You do not mention what generation electronics is being
used, but I was successful in interfacing one of those optos to a
System 7 CPU on my Hyperball (the auto-fire mod).

http://www.edcheung.com/album/album07/Pinball/hyperball.htm

Off hand, I cannot imagine why this would not work.  Perhaps you have
the wrong polarity somehow.  Perhaps you should check the voltage on
the lamp matrix with a scope.

I also know Martin Phillips has done a fair bit of research with
this.   I hope he will reply.

Edward Cheung CARGPB26

On Feb 10, 12:38 pm, lruper...@xxxxxxxxx wrote:

First let me clarify that I'm talking about this kind of optocoupler:

http://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Optocoupler.....

Not the kind found on the flipper buttons of WPC games. I've seen
those called optocouplers as well.

Here's my problem... I came up with an idea a while back to build a
replacement for the 6803 keypad that has a USB interface so you can
run marcos of button presses from a computer. My original plan was to
use optocouplers to replace the switches. That way I can have a
microcontroller drive the LED in the optocoupler and "turn on" the
transistor.

This was a great plan until I actually tested it. When I put the
transistor of the optocoupler into the circuit the MPU sees a switch
closure instantly. I expected that it would see the switch closure
when the LED inside the optocoupler was lit but shouldn't be able to
pass current through the transistor otherwise. I've abused the
optocoupler on a bread board in all configurations that I can think of
but I can't seem to figure out how the MPU is passing current through
the thing with the internal LED off.

I'm using 4n33 optocouplers but I'm not opposed to using any other
optocoupler that will work. I don't want to use relays.

Any thoughts?

Thanks in advance!- Hide quoted text -

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1) You will need a diode in series with the output transistor whatever
you do. Optotransistors work both ways.
2) If you connect a resistor from the base of the output transistior
to the emitter - say, 200 ohms - you will suppress counduction due to
noise.

But my suspicion is that you are dealing with a capacitative switch
pad. Got pictures?

.

Relevant Pages

  • Re: Semi OT: Using an optocoupler in a switch matrix
    ... Here is an example of the keypad. ... I will try putting a diode in series with the transistor. ... closure of one switch. ... transistor of the optocoupler into the circuit the MPU sees a switch ...
    (rec.games.pinball)
  • Re: Semi OT: Using an optocoupler in a switch matrix
    ... Here is an example of the keypad. ... I will try putting a diode in series with the transistor. ... closure of one switch. ... transistor of the optocoupler into the circuit the MPU sees a switch ...
    (rec.games.pinball)
  • Re: Semi OT: Using an optocoupler in a switch matrix
    ... input to the base of the opto transistor. ... I've done quite a bit with slow signal opto isolators for my job, ... transistor of the optocoupler into the circuit the MPU sees a switch ... I expected that it would see the switch closure ...
    (rec.games.pinball)
  • Re: Semi OT: Using an optocoupler in a switch matrix
    ... Do you see an open across the transistor with a DVM? ... voltage is probably in the 2V region. ... That is why I asked about the switch matrix voltage. ... transistor of the optocoupler into the circuit the MPU sees a switch ...
    (rec.games.pinball)
  • Re: Semi OT: Using an optocoupler in a switch matrix
    ... I don't see continuity through the transistor, ... I'll take a look at the switch matrix voltage with a scope and apply ... That is why I asked about the switch matrix voltage. ... transistor of the optocoupler into the circuit the MPU sees a switch ...
    (rec.games.pinball)