I'm trying to rewire an arcade game, and I need one button (a simple microswitch hooked up to the coin acceptor) to have a longer press than a coin passing by provides. I'm not sure exactly how long a press the software is looking for, but what would I need to wire in to lengthen the pulse? A capacitor, or maybe a retriggerable multivibrator? I'm a total novice, as you can see.

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    \$\begingroup\$ A multivibrator will give a chain of pulses. You want a monostable or one-shot. Millions of 555 timer examples on the web. \$\endgroup\$
    – Transistor
    Jun 5, 2016 at 9:40
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    \$\begingroup\$ Is there a reason why you cannot just keep the button pressed? If that is possible it is certainly the simplest solution electronically. \$\endgroup\$
    – caconyrn
    Jun 5, 2016 at 9:41
  • \$\begingroup\$ What voltage comes out of the coin acceptor when a coin is inserted? \$\endgroup\$
    – EM Fields
    Jun 5, 2016 at 11:02
  • \$\begingroup\$ @transistor: An astable multivibrator will output a chain of pulses, while a monostable multivibrator will output a single pulse for each triggering event. \$\endgroup\$
    – EM Fields
    Jun 5, 2016 at 11:16
  • \$\begingroup\$ @caconym If only, but the way those coin switches work is the coin rolls through the mech, then hits a microswitch for a fraction of a second. \$\endgroup\$ Jun 7, 2016 at 6:32

2 Answers 2


The astable multivibrator will send many electrical pulses once it is turned on,regardless of the fact that the button is pressed or not.Or,if you wire it so it activate on button press(and not by another source) it will send impulses with a time delay continously ,only while the button stays pressed.It's not useful.

If you wire a capacitor to the button,you won't obtain much,but you can get the task done if you build a monostable multivibrator with one,from discrete components,that is:http://www.electronics-tutorials.ws/waveforms/monostable.html. This kind of circuit will emit a continous pulse per press and will continue emitting until a capacitor discharges,even if it doesn't get an input signal anymore.Note that if you press the button again,before the output switches off ,the multivibrator will be triggered again and the output will constantly send the pulse,as if you kept the button pressed this whole time.This is what you need.You can also use a 555 chip , as transistor stated:http://www.electronics-tutorials.ws/waveforms/555_timer.html. There are many other examples out there,on the web.

Here is a simple one:


simulate this circuit – Schematic created using CircuitLab

When the button is pressed,the capacitor is charged instantly and when you let go,the capacitor will discharge through R2 and keep the transistor running as the light shines.

Note that, when you're rewiring ,you're going to need a transistor(BJT NPN) to act as another switch.Cut the button off ,place it in one of the circuits I mentioned ,connect the cut wire which carries the current from the source of the game to the collector of the transistor,the other to the emitter and the output of the multivibrator to the base.I don't really know how your game's setup works,so this paragraph might be inaccurate.If you want to know how to actually do it,post another question and give details about your setup.

  • \$\begingroup\$ With no resistance at all on the charging side this may be hard on the switch contacts. \$\endgroup\$
    – Ecnerwal
    Jun 5, 2016 at 19:51
  • \$\begingroup\$ It may be,but it all depends on the OP's setup and since he didn't specify anything,we cannot guide him on how he will effectively do what he wishes to \$\endgroup\$ Jun 6, 2016 at 4:32

The circuit shown below will give you a positive-going output pulse about 1/2 second long for any positive-going input pulse less than 1/2 second long.

The green trace represents the pulse from your coin acceptor, and the yellow trace represents the pulse which will now go where the pulse from the coin acceptor used to go.

Q1 isn't critical and just about any small NPN BJT will work

enter image description here

  • \$\begingroup\$ What values should be changed to make the output last 30 seconds with a 12V input? And is it possible to shut off the output given a reset signal? \$\endgroup\$
    – filippo
    Sep 18, 2020 at 16:24

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