Modified Coin Mechanism: How to add a key switch for free play

[DrZhark]

I'm about to finish my first ever build. I'll post pics of the finished cabinet once the artwork is installed.

I bought one of those brand new arcade coin door with dual coin mechanisms


And decided to mod it, so I could use the coin reject buttons as free coin buttons but only when a key switch was 'switched' on.
I wanted an LED to signal when the free play was turned on (Green) and when it was off (Red)






So I came up with this circuit:







It uses cheap parts:
-5vDC DPDT omron relay (about $2)
-PNP transistor 2N2907
-common cathode Red/Green LED
-4.7K resistor
-10K resistor
-1N34 diode
-Key Switch ($3)


The 2n2907 PNP transistor can be replaced with most PNP transistors
the red/green led can be replaced by one green and one red leds (but you have to make two holes on the coin door)
The diode doesn't need to be a germanium diode, it can be replaced with most usual diodes: 1N916, 1N4148 etc

The circuit uses a 5 volt source than can be obtained from the computer's power supply. The 5 volts are adequate to activate the relay and light the red/green led
When the key is in the off position, the red led is on and the relay is deactivated, so the 'B' switches are not connected in parallel with the normal coin switches.  When the key switch is turned on, the green light is on as well as the relay and the B switches are now connected in parallel with the normal coin switches.

I carefully added microswitches behind the coin reject push buttons, so it would remain functional but activate the free coin at the end of the push




Mounted the circuit in the back of the coin mechanism. 






It works flawlessly and I'm quite happy with it.

I wanted to share the circuit and instructions so others can use it, as I've learned so much from this forum and the book and at last I'm giving back my 2 cents.

[BGoulette]

I'm bookmarking this mothertrucker because it elegantly addresses something I've been considering! I have a neighbor who's giving me some coin doors/mechs from a parted-out machine, and I wanted to toss it all in a cab with which I plan to bribe my son: he can earn tokens which he can use to play, etc. Great idea!

[johnrt]

Yeah, that was a great idea and well executed! 

[Generic Eric]

Thanks for sharing!

[pbj]

Going to have to disagree with my cohorts.  You could have easily accomplished this with a toggle switch inside the coin door and avoided permanently butchering it.

[Thenasty]

pbj, I was thinking the same thing. I think DPDT switch should do it.

[BGoulette]

I wouldn't have drilled a hole in the coin door -- probably would have put it someplace less visible, but still accessible, but the general concept (and circuit) is what I find intriguing.

[Thenasty]

adventure is always fun.

[DrZhark]

pbj, I was thinking the same thing. I think DPDT switch should do it.

Indeed a DPDT is enough, but I wanted to use a key switch with a led 

[pbj]

Fine.  Could have accomplished your goal with a relay.  Transistors and diodes were completely unnecessary.

[DrZhark]

Fine.  Could have accomplished your goal with a relay.  Transistors and diodes were completely unnecessary.

The transistor is only used to control the green / red led. Nothing else. So the circuit was necessary to accomplish what I wanted. It is nothing complex anyhow. just one transistor, 3 resistors and 1 diode

[wxforecaster]

Since both the LEDs and switches are 5V, couldn't this have been accomplished with a SPDT relay and not a DPDT relay?

The 5V/Gnd coming from the key lock go to the coil lugs on the relay.

The 5V from the power supply goes to the COM on the relay.

The red LED and coin door switches non-ground connector wires (COM/5V) go to the NC on the relay.
The green LED and coin reject cherry switch connector wires (COM/5V) go to the NO on the relay.
The LEDs would need their normal resistor, but that's it.

Am I missing something?