Fun With Pinball

Animated Step Unit circuits from EM Pinball Machines

Step Units or Steppers are devices that manipulate more elaborate switch configurations.  Common examples include Ball Count units, Credit or Replay units and Score Reels.  Switches in Step Units can be configured as a series of independent switches operating together or as a single switch with multiple positions. The state of each switch is determined by the current position of the Step Unit.

All Step Units can step forward when their Advance or Step Up (SU) solenoid fires. Some Step Units can also step backward, either by just a single step or all the way back to the reset position, when their Reset solenoid fires.

A Non-Resetting Step Unit

Below is a simple circuit to demonstrate how a Non-Resetting Step Unit behaves when its Advance solenoid receives pulses.  Pulses in this schematic are generated by a Bally score motor just for illustration.

Non Resetting Step Unit circuit

The symbol in the upper right corner with the dashed lines is the portion of the Step Unit that is relevant to this circuit.  (There could be other parts of the same Step Unit elsewhere in a larger schematic.)  The small round circles represent the switch contacts on the Step Unit.  The double ended arrow represents the connection through the Step Unit that is currently being made. The double arrow moves from position to position as the simulation progresses.

The symbols in the upper left corner of the schematic are light bulbs to more clearly show which position the Step Unit is currently in.

Animated Step Unit circuit schematic

The simulation shows six pulses from a switch (MOTOR 11) on the #11 cam on the Score Motor activating the NEXT solenoid.  The ADV: NEXT label below the Step Unit symbol identifies the NEXT solenoid as its Advance solenoid so the Step Unit will step forward each time the NEXT solenoid activates.

The wave forms below the Motor Sequence Chart show when the NEXT solenoid fires and the position of the Step Unit as it changes during the simulation. (Note that the Step Unit label in the schematic drawing is "SELECT" so that is used to identify its wave form.)

Animated Step Unit Schematic at 58 degrees

This snap shot from the video shows the simulation just as the 2nd pulse from the MOTOR 11 switch is sent to the NEXT solenoid.  Both the wave form and the label below the Step Unit symbol in the schematic indicate that the NEXT solenoid is active, but the Step Unit itself has not yet changed from position 1 to position 2.

Although the Step Unit's Advance solenoid has fired, the Step Unit doesn't actually change positions until the solenoid relaxes. That is because the Step Unit's wiper mechanism advances with a return spring and not with the Advance solenoid.  For a better understanding of how that works watch the short video of the stepper in the Exhibits section.

Resetting a Score Reel

A Score Reel is a simple Non-Resetting Step Unit similar to the one in the example above.  During game play it advances a step each time its solenoid receives a pulse as demonstrated in the Score Motor examples.  At the start of a new game however the Score Reels must all reset back to zero.  This capability relies on a Zero Position or Runout switch on the Score Reel itself to indicate that it has reached zero and should not advance again until the game has started.

Below is a simplified reset circuit for a Score Reel.

Score Reel Reset circuit

The large Step Unit symbol (labeled SCORE REEL) represents the switches a Score Reel typically has.  Usually the Score Reel and the game schematic drawing rely on simple Zero Position switches but the symbol shown here is more explicit to better illustrate how those switches work.  The first pair of contacts in the Step Unit symbol represent a switch that closes when the Score Reel is showing a zero.  The nine remaining pairs of contacts together represent a single switch that opens when the Score Reel is showing a zero.

The SCORE REEL SU (step up) solenoid advances the Score Reel each time it gets a pulse.  The MOTOR generates pulses to advance the Score Reel through its MOTOR 1A switch.  The AT ZERO bulb is there just for clarity to indicate that the Score Reel has reset.

Animated Score Reel reset circuit

The simulation starts with the Score Reel in the 7th position (showing a 7), presumably the position from the end of the previous game. Once the Score Motor is started with the Start button pulses from the MOTOR 1A switch are sent into the SCORE REEL SU solenoid through the switches on the Score Reel.  The Score Reel advances when the SCORE REEL SU solenoid relaxes.  After three pulses the Score Reel has reached its zero position and there is no longer a path from the MOTOR 1A switch to the SCORE REEL SU solenoid.  The last two pulses from the MOTOR 1A switch have no effect and the Score Motor stops when the MOTOR 1C switch opens at the end of the cycle.

If the Score Reel requires more than five pulses to reach its zero position (starting from position 1 for example) the Score Motor would run through a second cycle to generate five more pulses using circuitry not shown in this simplified example. A working Score Reel requires no more than nine pulses to reach its zero position.

Animated Schematic Diagrams

Follow these links to other animated schematic diagrams: