Pinball machine - switch closure timing problem

Was hoping to do it by modifying the way it is done now with the cap. This switch closure only has to be extended in time by a fraction of a second to be able to be picked up reliably by the cpu. My thought was maybe since it can currently be extended with a small cap, maybe a larger cap could be used in conjuction with a certain value resistor so that it would still perform the same function, but 'bleed off' slower and extend the time. A last resort would be to hook up some kind of timed relay. Maybe a simple circuit that did the same thing with only a few parts like a simple transistor etc. would not be too bad, but have no idea on what it would need to perform the function of a 'timed switch closure'. thanks...

i don't understand how there can be ghosting in this case....a bigger cap would be like the switch was held closed for a longer time.... if a bigger cap can cause ghosting, then holding the switch closed for too long would also cause ghosting it seems... i would try a bigger cap and see what happens

Mark

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was hoping was possibly a simpler way of just extending using the cap method they already use (cap across the switch). Like bumping size of cap up and adding a resistor to 'bleed off' the cap slower (and longer.) Any other solution is welcome, something with solid state parts like maye a transistor and cap and resistor, preferably that would not need additional power supplly and could just be connected to the switch itself. thanks

I'd think that the problem is the switch doesn't close very well, and doesn't discharge the capacitor. Maybe there is some resistance in the switch/cap path, maybe the old cap is broken, but most likely the switch doesn't make too good a contact.

Thomas

--
Post a schematic of what you've got to
alt.binaries.schematics.electronic or to a web page somewhere so we
can see what we're dealing with.

You should crosspost - that way, when one person answers, everybody benefits.

...

I used to work on pinball machines. Have you burnished the contacts?

If that doesn't fix it outright, then just try stuff until it works. :-)

Good Luck! Rich

Take a look at such circuits as car dome-light extenders - basically you need to use the existing switch contact to trigger another relay (or MOSFET, whatever) via an appropriate timing circuit. It's "trivial" but the easiest thing to do would be to get a kit from a local hobby store (or on-line). I doubt that I'm in your area so maybe a suggestion from the gallery......?

Cheers.

Ken

There are two separate switch systems used in most pinball machines, the switches that are attached to the switch matrix and what is usually referred to as "continuous" switches. A switch matrix allows a relatively small number of wires to read a large number of switches by stepping or strobing through a certain number of rows of switches. What they do is in effect move the ground from one bank of switches to another. In fact, since they all used 8 bit port on their systems the standard switch matrix was an 8 by 8 matrix, which allows the reading of

64 switches with 16 control lines. These switches are by default debounced to what ever strobe rate the matrix works at. Adding a capacitor here can help, but only to a very small extent. Putting a large capacitor might actually cause the switch to get worse. It all depends on how good the strobe driver is. It is just a bipolar transistor and is no where near a great ground for the cap. If the switch you are having problems with is on the matrix then I wouldn't play with adding caps, I would look at things like contact resistance, contact gap, mechanical problems with actuation, or even the 1N914 blocking diode that is on the switch. On the other hand the "continuous" switchess were just directly read input ports that were used for switches that were attached to devices that operated way too fast for the strobe rate of the matrix. Things like sling shots and, primarily, the thumper bumpers. The addition of capacitors there could make a difference, but the value would need to be selected to make sure that the response time to successive events isn't dampened to the point it ruins game play.

Jim

no this is a brand new machine and good switch, it is a common problem on this model (this particular switch is the only target on the game that can really get slammed quickly and commonly has trouble scoring). This manufacturer doesn't even put caps on their switches anymore. I am experimenting with caps to try to eliminate the problem (for me and other owners)...Frenchy

This is the type I am dealing with here. And in the old days (80s) they would put caps on these, .05 uf, if the switch was particularly prone to hard fast hits. This is where I am hoping to stretch the time out with maybe bumping the cap and adding a resistor.

Yeah this is like one company used in the 80's also for 'special' solenoids where they went with a 22uf cap and a 100 ohm resistor to stretch out the switch closure time read by the solenoid driver so it would pulse a kicker or bumper longer for more power. So I am wondering if I can have something in this set up and the one above....maybe a smaller capacitor than this, + a resistor of some value.

In my experience the real problem has to do with the switch itself, no matter whether it is new or not. The contact tension should be increased for a start but since I don't know the switch construction this may not be possible. Contact bounce is a common problem with relays using long contact spring arrangement as used in older telephone exchanges and the spring tension is adjusted by 'stroking'. The suppression capacitor simply 'irons out' any remaining bounce artefacts and putting a larger cap in will not improve the situation.

The real solution is to incorporate 'bounce elimination' using simple logic so that a '1-and-1-only' switch closure is produced.

This page describes the problem and how to overcome it (2nd cct applies to single make switch)

A paper on debouncing goes into more detail

And to do six switches at once use the MC14490

no matter whether it is new or not. The contact tension should be increased for a start but since I don't know the switch construction this may not be possible. Contact bounce is a common problem with relays using long contact spring arrangement as used in older telephone exchanges and the spring tension is adjusted by 'stroking'. The suppression capacitor simply 'irons out' any remaining bounce artefacts and putting a larger cap in will not improve the situation.>>

These are brand new gold-contact switches. No relays, this is solid state stuff on a new machine. Pretty sure they already have put debouncing circuitry or software in pinballs for a long time to prevent false excess scoring etc. Again the basic problem is just sometimes certain pinball switches don't quite close long enough for the matrix to pick it up, even if the switch itself is perfect, was done by the factories for years on certain switches they knew would have this problem due to a ball really zipping over a rollover switch extremely fast or a target getting hit hard. In fact the switches in question work better when softly hit since then the contacts are closed longer. Hard hits where the contacts are really making even better contact and with longer stroke due to more movement of the switch, but the total time of switch closure is shorter due to the speed and rebound off the switch. Particular swtich in question is same thing, works fine on glancing hits since then it is closed longer than hard slams...Frenchy

Ok I will keep this in mind, there is nothing that will piss a pinball player off more than something that is supposed to score when you hit it, and it doesn't. Bugs in the software can be tolerated to a point, but when it comes down to a target acting like you never even hit it in the first place, that's another story. (Electromechanical games did this routinely since they could only do one thing at a time but that was expected by players...not so with electronic games.) Right now I have a 4.7 uf cap and a 150 ohm in series across the switch and seems to be working flawlessly (so far anyway). If this ends up not being foolproof I may get back to you on how complicated this opto thing would be. thanks!....Frenchy

Nope, multiple balls on modern games. I don't see a problem in simply extending the switch closure on one switch, the games routinely have mulltiple balls going at once, have some switches that are closed for long periods or all the time, etc. As for ghosting, not sure what is meant by that but was told this can happen if the cap is made too large. AS if it could cause false reads on other switches when the problem switch was not even closed, due to the cap doing something unintended. Maybe would make a difference if cap was polarized or non polarized? Maybe that could make a difference. But if the worst thing a cap can do is make the switch read as closed all the time, I don't see that as ghosting either - just a stuck switch.

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Even if it is martixed, I think a cap directly across the switch in question may help. Note I'm saying the cap should be across the switch, not from the switch to ground.

Did you try it?

If the switch closure is short and the scanninbg is slow, I can see how it could miss, but the cap should help because when the switch closes even breifly, it will discharge the cap and the cap will "remember" that the switch was closed until the scan comes around to read it.

Mark

All solid state pinball switches are of the type where if held closed, will not cause a 'multiple scoring', they will simple score once. Some might keep telling the machine to keep trying to kick a ball out of a hole etc. but this one I'm dealing with is just a one-shot target so not an issue. I understand the concept of the cap and the resistor being across the switch, it's the values desired I am totally in the dark about. Maybe just comes down to experimentation. But I also don't want to risk damaging anything by using too big a cap or too small a resistor etc. All I have to go by is the manufacturers using a .05 cap by itself on certain switches...Frenchy

It seems that by 'ghosting', it is meant for example that if a diode on one switch in a switch matrix fails, it can cause false closures on other switches in the same row and/or column. But this is due to a shorted part. Not sure why using a cap over a switch could or would cause this to occur also. Might depend on using too big of a cap, too small of a cap, if cap was polarized or not etc. Ohhhh I don't know, I fix pinballs, all I know about electronics is how to put batteries in a flashlight, that's why I'm buggin you guys! ; )

Frenchy

Once upon a time I had to deal with a prototype Williams Dracula that had a problem recognizing a matrixed switch even if it were engaged very positively, so I know it does happen. I ended up making a little circuit with an opto as the interface to the matrix and an Op Amp set up as a comparitor to stretch the length of time it appeared to have a closed switch. I know it worked for the duration of the trade show. Williams had +12VDC available under the playfield for use with their opto boards and so on, so it was a snap to steal a little power. I don't know what resources you have available on your particular pinball machine, but it is something to think about.

Jim