why is there a capacitor in my player 1 coin mech micro switch?

[BC_Jeffro]

hi i was going to trade coin doors on my Bosconian mini with my super pac and noticed this on my super pac coin door mirco switch
 why is there a cap there?

[matsadona]

Not sure... but maybe to eliminate contact bounce? Or is it the opposite - i.e. that the coin signal will last longer so that the game has a better change noticing it maybe?

[Gray_Area]

I recommend titling your thread "why is there a capacitor in my coin mech?".  Or, shortly, "Capacitor in my coin mech?"

[BC_Jeffro]

ok

[paigeoliver]

That is actually the switch, the mech is the the tan plastic jobby above that.

Game probably wasn't triggering coin drops every time for some reason and that somehow fixed it.

[BC_Jeffro]

ya i know its not on mech but on micro-switch (will change post title)

so its not a huge mystery there are reasons for doing this
thanks

[WindDrake]

Contact debounce & contact noise filtering.

[BC_Jeffro]

 
thanks

[rCadeGaming]

That's interesting.  How many microfarads (uF, should say on the side)?

[brad808]

For some reason this isn't sinking into my head. Can someone explain the dumb dumb version as to how this is doing something useful?

[PL1]

For some reason this isn't sinking into my head. Can someone explain the dumb dumb version as to how this is doing something useful?

The Ikalogic website de-bounce page explains that pressing and releasing a button can cause spring-loaded contacts to bounce (picture dropped silverware) resulting in voltage spikes like this at the encoder input:


The discharge and re-charge of the capacitor during the press and release smooths the voltage like this:


By choosing a capacitor that charges and discharges at the right rate, you allow the encoder to record legitimate credits and block false ones.

Software or firmware filters out any remaining ripples -- "Source of error" in second pic.


Scott

[brad808]

Awesome, that makes good sense. Thank you.

Sent from my Galaxy Nexus

[rCadeGaming]

By choosing a capacitor that charges and discharges at the right rate

What's the math in choosing the right capacitor?

[WindDrake]

Picking the right cap is part voodoo, part conventional wisdom for debouncing via noise suppression.

Voltage isn't important. Just pick a cap rated to (typically) 25-33% higher then your operating voltage. This is just headroom over-speccing.

Value is handled by our friend the RC Time Constant.

"But WD!" you'll say. "That takes a pullup resistor!"

Then I remind you that the input is either internally pulled up (90's and onwards) or has a pullup at the board.

http://www.ganssle.com/debouncing-pt2.htm

Math is there. Here's the short of it: Most switch bounce lasts less then 10-20msec. Most debounce caps you'll ever see are 0.1 or 1uF.

Larger caps put a big honking delay on the line, which can cause the board to ignore a coin drop that's quick behind the last one.

My guess is that's why that cap is there. That, or that cab's original board had some serious gremlins.