A friend recently asked for some help configuring electromechanical (EM) pinball machines at his location to charge 2 coins per play (e.g. 50 cents per play). Most EM games when they were new had circuit options for one coin per play or one coin for multiple plays (or credits) and were not able to charge two coins per play.
Another friend once mentioned to me that he converted some of his games to charge two coins per play by adding a circuit using a Score Reel. While it made sense to me at the time I never really sat down to figure out exactly how to do it. Now I had a good reason to sort it out.
The basic problem with charging two coins per play is that the game needs to remember whether or not one coin has been inserted which would give and the player 1/2 a credit towards a game. Adding a simple relay to remember the first coin drop could work, but the relay might need to remain active indefinitely if the player walked away after dropping the first coin. An interlock or latch-type relay could also work, but those are less common and more expensive that a simple relay.
A Score Reel is a good choice because it can remain in any position indefinitely without using any power, and most Score Reels have a contact board that identifies which position (of the 10 possible positions) the reel is in. The contact boards are used to award replays for high scores, and matches at the end of the game.
By rewiring the contact board of a Score Reel, a simple circuit can be built that allows the game to start every other time a coin is dropped through the coin chute.
The animation below shows how a Score Reel can be rewired to fire the Coin relay every other time the switch on the Coin Chute closes. The Coin relay (or, in some games the Start relay) is what causes the game to reset and start a new game.
In the middle of the schematic diagram above is the Score Reel Coil that advances the Score Reel from one position to the next. It fires each time the Coin Chute switch closes, or each time a coin is dropped through the Coin Chute.
At the top of the schematic is the Coin relay coil that starts a new game. It also fires when the Coin Chute switch closes, but only if there is also a connection through the rewired Score Reel contact board.
At the start of the animation the Score Reel is at 0 so no connection is made through the Score Reel. But when the Coin Chute switch closes the Score Reel Coil fires which advances the Score Reel from 0 to 1. At this point there is a connection through the Score Reel so the next time the Coin Chute switch closes the Coin relay will fire in addition to the Score Reel Coil.
The process continues as coins pass through the Coin Chute and close the Coin Chute switch. Each time the Coin Chute switch closes and the Score Reel is at an odd numbered position (1, 3, 5, 7 or 9), the Coin relay fires and the game resets (or adds another credit). The modified Score Reel has essentially been converted to a simple alternator circuit
The short video below shows how the circuit above behaves. The black button represents the Coin Chute switch and the light bulbs indicate when the Coin relay would fire.
2 coins per play circuit demonstration
Note that the End of Stroke, and 0 and 9 position switches have all been removed from the Score Reel. Since they're not used removing them should make the Score Reel more reliable.
Although most electromechanical games didn't ship with a 2 coins per play circuit, it was an option that could be ordered from some manufacturers. It may have been more common in games shipped overseas. Here for example is a Bally part that offers the 2 coin per play option.
If you look carefully you might recognize that this too closely resembles a modified Score Reel.
Follow these links to other animated schematic diagrams: