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Maker Pro

Pinball switch closure timing problem



Jan 1, 1970
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 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? I am pretty good at
fixing pinballs, but electronics theory is not my calling. thanks for
any assistance anybody can give me. Thanks!