Pinball machine - switch closure timing problem

[frenchy]

I'm posting this to a few electronics newsgroups poking around for a
possible answer...

For years the pinball companies used a small .047 uf capacitor across
some switch terminals for switches that could be closed and reopened
very quickly like a target getting slammed particularly hard. The
capacitor would increase the 'closure time' that the CPU would read the
switch as closed, long enough to help it pick up the switch closure.
These switches are just simple two blades and contacts, with one wire
to the cpu, the other wire thru a diode to isolate it within the matrix
of switches in the game, and the capacitor may or may not be across the
terminals also.


I'm having a problem with a particular swtich that the cap fix is
working, but not completely. Some hardhits will still not register.
Tried putting bigger cap on it with improved results but I've read that
too big of a cap can cause 'ghosting' where it might start causing
false closure reading on other switches in the matrix. So my question
is....


Is there a simple formula where one could increase the size of the .047
cap or .1 cap or whatever is being used, but put in in series with a
resistor, to lengthen the time that it is doing it's thing of
lengthening of the closure to the cpu? I.e if I wanted to use a cap
10x bigger, what resistor could I put in series with it to be sort of
like the smaller cap without the resistor, but length of discharge
would be stretched out? Or is this possible? Maybe a diferent more
complicated approach is necessary to get this one switch to be sensed
as 'closed' longer. I am pretty good at fixing pinballs, but
electronics theory is not my calling. thanks for any assistance
anybody can give me. Thanks!

 

[Ken Taylor]

"frenchy" <mf101723@msn.com> wrote in message
news:1111454517.017086.226600@l41g2000cwc.googlegroups.com...

I'm posting this to a few electronics newsgroups poking around for a
possible answer...

For years the pinball companies used a small .047 uf capacitor across
some switch terminals for switches that could be closed and reopened
very quickly like a target getting slammed particularly hard. The
capacitor would increase the 'closure time' that the CPU would read the
switch as closed, long enough to help it pick up the switch closure.
These switches are just simple two blades and contacts, with one wire
to the cpu, the other wire thru a diode to isolate it within the matrix
of switches in the game, and the capacitor may or may not be across the
terminals also.


I'm having a problem with a particular swtich that the cap fix is
working, but not completely. Some hardhits will still not register.
Tried putting bigger cap on it with improved results but I've read that
too big of a cap can cause 'ghosting' where it might start causing
false closure reading on other switches in the matrix. So my question
is....


Is there a simple formula where one could increase the size of the .047
cap or .1 cap or whatever is being used, but put in in series with a
resistor, to lengthen the time that it is doing it's thing of
lengthening of the closure to the cpu? I.e if I wanted to use a cap
10x bigger, what resistor could I put in series with it to be sort of
like the smaller cap without the resistor, but length of discharge
would be stretched out? Or is this possible? Maybe a diferent more
complicated approach is necessary to get this one switch to be sensed
as 'closed' longer. I am pretty good at fixing pinballs, but
electronics theory is not my calling. thanks for any assistance
anybody can give me. Thanks!

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

 

[Zak]

frenchy wrote:

For years the pinball companies used a small .047 uf capacitor across
some switch terminals for switches that could be closed and reopened
very quickly like a target getting slammed particularly hard. The
capacitor would increase the 'closure time' that the CPU would read the
switch as closed, long enough to help it pick up the switch closure.
These switches are just simple two blades and contacts, with one wire
to the cpu, the other wire thru a diode to isolate it within the matrix
of switches in the game, and the capacitor may or may not be across the
terminals also.


I'm having a problem with a particular swtich that the cap fix is
working, but not completely. Some hardhits will still not register.
Tried putting bigger cap on it with improved results but I've read that
too big of a cap can cause 'ghosting' where it might start causing
false closure reading on other switches in the matrix.

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

 

[Mark]

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

 

[frenchy]

Ken Taylor wrote:

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......?

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

 

[John Fields]

On 22 Mar 2005 06:46:56 -0800, "frenchy" <mf101723@msn.com> wrote:

Ken Taylor wrote:
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......?

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

---
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.

--
John Fields

 

[James Beck]

In article <1111501934.892521.294900@f14g2000cwb.googlegroups.com>,
makolber@yahoo.com says...

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


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

 

[Rich Grise]

On Mon, 21 Mar 2005 17:21:57 -0800, frenchy wrote:

I'm posting this to a few electronics newsgroups poking around for a
possible answer...

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

For years the pinball companies used a small .047 uf capacitor across
some switch terminals for switches that could be closed and reopened
very quickly like a target getting slammed particularly hard. The
capacitor would increase the 'closure time' that the CPU would read the
switch as closed, long enough to help it pick up the switch closure.
....
Is there a simple formula where one could increase the size of the .047
cap or .1 cap or whatever is being used, but put in in series with a
resistor, to lengthen the time that it is doing it's thing of
lengthening of the closure to the cpu? I.e if I wanted to use a cap
10x bigger, what resistor could I put in series with it to be sort of
like the smaller cap without the resistor, but length of discharge
would be stretched out? Or is this possible? Maybe a diferent more
complicated approach is necessary to get this one switch to be sensed
as 'closed' longer. I am pretty good at fixing pinballs, but
electronics theory is not my calling. thanks for any assistance
anybody can give me. Thanks!

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

 

[frenchy]

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

 

[frenchy]

<< 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 switchesThese
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.>>>

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.

<<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. >>

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.

 

[frenchy]

<<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. >>

This switch is on a brand new machine, of which other owners invariably
have the same problem with this switch.
So this is not a problem of faulty parts from reading rec.games.pinball
and other owners reports. It's just a switch
in the game that is really whacked, the only stand-up target in the
game that is really whacked like this. All other switches in the game
are microswitches, or softly hit targets, or infrared led sensor types,
and don't have this problem. Targets are all gold-plated points.
Again it is just a similar case of what pin makers dealt with in the
80s of having to put caps on certain switches from the outset knowing
they get fast hits, and this company does not use caps at
all....Frenchy

 

[Ken Taylor]

"frenchy" <mf101723@msn.com> wrote in message
news:1111502816.528008.35480@l41g2000cwc.googlegroups.com...

Ken Taylor wrote:
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......?

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 note the comments of others more familiar with pinballs in particular, and
your comment that it appears to be a design fault in the machine.

Given all that, it would seem to me that it's relatively easy to make up a
small circuit which will run a MOSFET or relay using the existing switch as
the trigger, and vary the amount of time you keep the output closed. This
way you can do some controlled experiments in whether the technique of
stretching the closure time is even valid in the first place. Once you know
it works you can then decide how to do it on a more permanent basis.

Cheers.

Ken

 

[Ross Herbert]

On Tue, 22 Mar 2005 16:00:24 GMT, James Beck
<jim@reallykillersystems.com> wrote:

In article <1111501934.892521.294900@f14g2000cwb.googlegroups.com>,
makolber@yahoo.com says...
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


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

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)
http://www.play-hookey.com/digital/experiments/manual_pulser.html

A paper on debouncing goes into more detail
http://www.ganssle.com/debouncing.pdf

And to do six switches at once use the MC14490
http://thayer.dartmouth.edu/~engs031/databook/mc14490.pdf

 

[frenchy]

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.>>

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

 

[James Beck]

In article <1111559533.599800.164580@o13g2000cwo.googlegroups.com>,
mf101723@msn.com says...

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.

This switch is on a brand new machine, of which other owners invariably
have the same problem with this switch.
So this is not a problem of faulty parts from reading rec.games.pinball
and other owners reports. It's just a switch
in the game that is really whacked, the only stand-up target in the
game that is really whacked like this. All other switches in the game
are microswitches, or softly hit targets, or infrared led sensor types,
and don't have this problem. Targets are all gold-plated points.
Again it is just a similar case of what pin makers dealt with in the
80s of having to put caps on certain switches from the outset knowing
they get fast hits, and this company does not use caps at
all....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

 

[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

 

[Zak]

Mark wrote:

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

Well,

It sounds like it is a matrix. There is only one ball: thus only one
switch is engaged.

The capacitors extend the time that a single switch seems engaged. A
rapid succession of two switches could make it appear that two other
switches are also engaged...


Thomas

 

[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.

 

[Mark]

Rich Grise wrote:

On Mon, 21 Mar 2005 17:21:57 -0800, frenchy wrote:

I'm posting this to a few electronics newsgroups poking around for
a
possible answer...

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

For years the pinball companies used a small .047 uf capacitor
across
some switch terminals for switches that could be closed and
reopened
very quickly like a target getting slammed particularly hard. The
capacitor would increase the 'closure time' that the CPU would read
the
switch as closed, long enough to help it pick up the switch
closure.
...
Is there a simple formula where one could increase the size of the
..047
cap or .1 cap or whatever is being used, but put in in series with
a
resistor, to lengthen the time that it is doing it's thing of
lengthening of the closure to the cpu? I.e if I wanted to use a
cap
10x bigger, what resistor could I put in series with it to be sort
of
like the smaller cap without the resistor, but length of discharge
would be stretched out? Or is this possible? Maybe a diferent
more
complicated approach is necessary to get this one switch to be
sensed
as 'closed' longer. I am pretty good at fixing pinballs, but
electronics theory is not my calling. thanks for any assistance
anybody can give me. Thanks!

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

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

 

[Terry Given]

frenchy wrote:

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

Hi Frenchy,

I think you are on the right track. Its been 15 years since I had to
repair a pinball.....

The switch matrix gets scanned frequently - guess every 64ms (numbers to
make maths easy). If there are 64 switches, then each switch gets
scanned every 1ms. Just like ADC sampling, the worst-case is a switch
gets hit the instant after the micro looks at it. If such a switch
closure lasts less than the entire scan duration (ie how long it takes
to have another look) it will be missed.

Conversely if a switch closure lasts longer than the scan duration it
will be read twice - if it is an intermittent contact, this may register
as two hits, perhaps this is what is meant by "ghosted" - hard to say
really, without knowing exactly what the software does.

If you place a cap across the switch, then switch closure will discharge
it with a time constant (Rswitch + Rseries + ESR)*Ccap. The peak current
flowing through the switch is Vopen/(Rswitch + Rseries + ESR). Rswitch
ought to be extremely low, but increases as the switch craps out. ESR
may be low, depending on cap type, but it may also be many tens of Ohms.

The switch then opens, and the cap starts to charge up through the
matrix pullup transistors/resistors. These are usually current limited
in some way, giving a not-too-high charging current to the cap.

You want a nice, fast discharge and a slow charge. For fastest
discharge, set Rseries = 0. Beware the peak current through the switch
though, especially for large C. Many electrolytics have high enough ESR
that this alone will protect the switch. Note that smps electrolytics
are (or bloody well ought to be selected for extremely low ESR....

To ensure a slow charge, put a series R between the switch/cap assembly
and the matrix, thusly:

Original:
|
----------|-----+-- [switch to V+]
| |
| |
| |
| o
| /
+---o
|
|
[switch to 0V]


Modified:
|
----------|-----+-- [switch to V+]
| |
| [Rcharge]
| |
| o--[+Cap]--+
| / |
+---o----[Rdis]--+
|
|
[switch to 0V]


Choose Rdis to protect the switch, and Rcharge > Rdis to stretch the pulse

Cheers
Terry