Coin Multiplier Board (CMB) :

Dropping 1 Coin Looks Like Multiple Coins To Machine

This is a very simple board of my own design. The board shown below is a prototype that was built from an old board previously designed for another project. It takes in pulses from the standard coin crediting switch and outputs crediting pulses to the coin input of the game board. Specifically, it outputs 4 pulses for each 1 pulse that it receives from the coin switch. If you drop a Canadian Loonie into a Loonie compatible coin mech., the big coin will activate the coin switch once, thereby sending a single pulse into the CMB. The CMB will then generate 4 accurately timed pulses out so that the game will grant four quarter credits. The output pulses each last 250ms and are spaced 500ms apart to give the game time to register them. Four pulses take 3 seconds to complete. If you drop more Loonies in less than that time, the CMB will not miss them. It will add 4 more credits for each coin dropped even if it is still sending out pulses. There is virtually no limit to the number of coins that you can drop one right after the other because the pulse counter is very deep. The CMB also "debounces" the coin switch using a 150ms delay. It is unlikely that anyone would drop coins into a mech faster than this period. However, all of the time periods that I've just mentioned are fully programmable so if in the future something needs to be adjusted, there's no problem there.

The CMB also has a single LED indicator on it. It blinks a few times upon powerup so you can see that it is alive. It blinks once for each output pulse (maybe call it one blink per quarter out) so you can see that it is crediting properly. It also can indicate a shorted coin switch. If the switch gets stuck closed (or the line is shorted to ground) for more than two seconds, the LED will blink quickly and continuously to indicate the fault. If the fault condition disappears (i.e. the switch opens again), then normal operation will resume automatically.

A recent addition to the functionality, the CMB is now user programmable in terms of setting the number of pulses to output per single input pulse.

To hook up the CMB, all you have to do is cut the coin switch wire and install the CMB between the two ends of the wire. You also have to connect a power source. Any DC power from +5V to +18V will make the board work but you should use the same voltage used by the game board switch input logic.

You should physically mount the CMB using 4 plastic PCB standoffs or spacers using four #4 screws. The CMB is very light weight so it could be left hanging (not recommended) or just wire-tied to the existing wiring harness. Locate the coin mech switch that you want to have trigger the CMB and follow the switch wire (on the active side, not the ground side) back toward the game board until you find a convenient place to mount the CMB. Once the CMB is mounted, cut the switch wire and connect the switch-end to the CMB's switch-input terminal. Connect the game-board-end of the wire to the switch-output terminal of the CMB. Then find a convenient +5V supply wire and splice a new wire into it and run that wire to the CMB. All that's left now is to connect the CMB to ground (0V). You can find the ground return wire that comes from the coin-mech switch or any other switch that shares the ground and splice into that with a new wire and connect that to the CMB ground terminal. Alternatively, connect to any power supply or signal ground on the game board or a power regulator board. Bringing +5V and ground together from the game board is highly recommended.

Caution: Most game boards use +5V logic for their switch inputs so that's what you should use to power the CMB. If you must power the CMB from supply voltage of 6V or higher, you should probably remove the pull-up resistor from the output of the board. On the prototype board, that is a 2k resistor located at position D1. The game board will always have its own pull-up resistor anyway. There is a pull-up resistor on the CMB only so that you can test for its output when it's not connected to anything. A future revision of the CMB will likely have a solder jump option to choose either a pull-up to the power supply or to +5V regardless of the voltage supply the board.


Coin Multiplier Board Hookup Drawing
Coin Multiplier User's Guide


What lead me to do this?

Someone asked nicely. Building and programming little bitty microcontroller projects like this is what I do for a living so it was a piece of cake. If this device becomes popular, I will design a dedicated PCB for it and sell them.

If you want more information or have questions. Just email me.


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Last Updated: Feb. 22, 2009