Small Boards
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Fun With Pinball

Small boards

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01_Solenoid_thSolenoid 02_Relays_thRelays 03_Pop_Bumper_thPop Bumper 04_Flipper_thFlipper
05_Score_Reels_thScore Reels 06_Chimes_thChimes 07_Drop_Target_thDrop Target 08_Vari_Target_thVari Target
09_Roto_Target_thRoto Target 10_Disappearing_Post_thDisappearing Post 11_Ball_Lifter_thBall Lifter 12_Magnet_thMagnet
13_Credit_Unit_thCredit Unit 14_Ball_Count_Unit_thBall Count Unit 15_Stepper_thStepper 16_Score_Motor_thScore Motor
17_Captive_Ball_Unit_thCaptive Ball Unit 18_Projection_Unit_thProjection Unit 19_Spin_Unit_thSpin Unit  

These small boards were built to demonstrate individual devices from pinball machines.  They all have 24v (for relays and solenoids) and 6v (for lamps) AC power wired along the back.  Each board attaches to its neighbor on the left side to form a string of display boards wired together.  The first board in the string attaches to a transformer which supplies power to all boards in the string.  Using the same connectors on each board allows the boards to be laid out in any order, and makes it easy to swap out or remove a board if it breaks down.

Each of the display boards is shown below with its instruction card which is typically propped up behind the board.


Solenoids drive most of the motion in a pinball machine and are featured in most of the other displays.  This solenoid is purposely weak and slow moving to show how it can lift the steel plunger when power is applied.  Normally solenoids move their plungers so quickly that they are hard to follow.

Solenoid Solenoid instruction card

This video shows how the solenoid works.  In this case the steel plunger is attached to a wooden dowel with a round target at the top to better show the motion of the plunger as it is drawn into the solenoid.

Solenoid demonstration

For a more in depth explanation of how solenoids convert electricity into motion, visit the Solenoids, Relays and Electromagnetism page.


Relays are smaller and weaker than solenoids and are usually only used to activate or hold switches to enable features and lights, or to release mechanisms that were activated by a solenoid (as in the Disappearing Post, Zipper Flippers and others below).  This board includes a simple relay, an interlocking relay which can stay in either position indefinitely without power, and a relay configured as a miniature stepper that turns a cam to open and close a switch.

Three different types of relays Relay InstructionsRelay instruction card

The video below shows how the various relays behave.

Relay demonstration

For a more in depth explanation of how relays convert electricity into motion, visit the Solenoids, Relays and Electromagnetism page.

Pop Bumpers

Perhaps the single most recognizable feature of a pinball machine, the Pop Bumper (or Jet Bumper) can kick a ball away that is approaching from any direction.

Pop Bumper Pop Bumper InstructionsPop Bumper instruction card

Pop Bumpers can fire several times per second and are too fast to easily discern the sequence of events.  The version below uses a microcontroller and a couple of small motors to animate the pinball and pop bumper in slow motion. 

Slow Motion Pop Bumper Slow Pop Bumper InstructionsSlow Pop Bumper instruction card

Watch the video to see these pop bumpers in action.

Pop bumpers close up and slowed down


While flippers appear on all pinball machines now they weren't invented until the late 1940s.  Before then players had to nudge the ball around the playfield without tilting the game or rely on ball kickers that would only fire when the ball closed the appropriate switch.

FlipperFlipper Flipper instruction card

Zipper Flippers work just like the Flipper above but with the added feature that they can swing towards eachother to close the gap and prevent the ball from draining between them while remaining fully functional.  They would open and close during the game based on which targets were hit.  Zipper flippers were used on relatively few pinball machines.

Zipper Flippers Zipper Flipper instruction card

Watch the video below for a better idea of how flippers work or, for even more detail visit the Flippers, coils and power page.

How flippers work

Score Reels

Score reels are simple counters similar to mechanical odometers in older cars.  Each reel can be advanced individually (to add 10 points, or 100 points for example), or advances when it's lower neighbor rolls over from 9 to 0 (from 89 to 90 for example).  Each reel also has a separate reset circuit used at the start of a new game that lets it advance only until it reaches 0, where it stops.

Score_ReelsScore Reels Score_ReelsScore Reel instruction card

The score reel video below shows how the 9 position and zero position switches open and close as the score reel advances.  The 9 position switch is used to advance the next higher score reel and the zero position switch is used when resetting the score reel to 0.  Most score reels have no way of knowing what digit is showing other than 0 and 9.

Score reel demonstration

You may have noticed in the video that when a score reel resets to zero it advances its higher neighbor by one.  This is not the normal behavior.  A complete pinball machine has extra circuitry not present on this demonstration board to prevent this from happening.

Chimes and Knocker

Most pinball machines make sounds of one sort or another.  Electromechanical games used chimes, bells and knockers.  Chimes and bells of different tones were used for different point values (e.g. 10 point chime, 100 point chime, etc.) while the knocker was typically used when a free game or special was awarded.

ChimesChimes and Knocker ChimesChimes and Knocker instruction card

A set of chimes and a knocker are demonstrated in the following video.  (An example of a bell can be seen in the video for the captive ball unit below.)  In the chimes, solenoids are mounted below a set bars of different lengths similar to the bars in a xylophone and the plungers strike the bars when the solenoids are activated.  The knocker works the same way, but the plunger strikes a plate typically mounted to the pinball machine cabinet which makes the entire cabinet a sort of resonant chamber.

Chimes and knocker demonstration

Note that the motion of the plungers is the same as shown in the video for the solenoid above, just much faster.

More detail and animations explaining how chimes generate different pitches is on the Chimes, Vibrations and Pitches page.

Drop Target

A Drop Target disappears into a slot in the playfield when hit by the ball.  After points are scored, the solenoid below the playfield resets the drop target to its starting position.

Drop_TargetDrop Target Drop_TargetDrop Target instruction card

The drop target is held in the up position by a notch on its shaft that rests on a small ledge just below the playfield.  When struck by the ball (or by a finger in the following video) the target is pushed back and falls off the ledge, pulled down by the outstretched spring.  When the solenoid is activated, it pulls the target back up, stretches out the spring again and props the drop target notch back up on the ledge.

Drop target demonstration

There are three switches mounted to this assembly.  The bottom two switches tell the game whether the drop target is up or down.  In this demo the two switches are wired to lights instead to indicate the target's position.  The top switch opens when the drop target is reset to its up position.  It is used to cut power to the solenoid.

Vari Target

The spring loaded Vari Target registers how hard it was hit by the ball.  A soft hit only pushes it back a little bit while a harder hit will push it back further.  The points awarded vary according to how far back the Vari Target was pushed.

Once the points have been scored, the relay fires to reset the Vari Target to its starting position.

Vari Target Vari-Target InstructionsVari Target instruction card

The video below demonstrates how the Vari Target works.  The armature on the relay acts like a ratchet to let the target swing back and hold it at its last position.  Switch blades attached to the back of the target arm connect an upper and lower contact together to complete a different circuit for each position.  In this board, each circuit lights a bulb to show how far back the Vari Target was pushed.

The relay armature is pulled out of the way to let the target reset to its starting position.  A switch in the lower left is closed whenever the target is not in its reset position.  This tells the pinball machine that the target has been hit and points should be awarded.  In this board, the switch is used to cut power to the reset relay once the target has been reset.

Vari target demonstration

Roto Target

A Roto Target only presents three targets at a time above the playfield, but during the game the wheel spins periodically to expose a different set of three targets.  Regardless of its position, the Roto Target can tell which of the targets was hit (1, 2 or 3) and award points accordingly.  It does this with a set of rotating contact switches on the back of the roto target similar to those shown in the video for the stepper below.

Roto_TargetRoto Target Roto Unit instruction card

The Roto target uses a double ratcheting mechanism to spin in one direction, then roll back a bit in the other direction to center the target as the spinning stops.  This mechanism is shown in the video below.

Roto target demonstration

Disappearing Post

The Disappearing Post is an obstacle that would appear and disappear periodically during a game.  Typically it was installed between the flippers and could prevent the ball from draining between them when in the up position.

Disappearing Post Disappearing Post instruction card

The post is lifted into the up position by a spring wrapped around its shaft.  The spring is compressed when the post is lowered by the bottom solenoid.  The post is held in the lower position by a plastic latch mounted to the shaft.  The smaller relay activates to release the latch and let the post lift to the up position as shown in the video below.  Switches mounted to the back of the unit turn the lights on when the post is in the up position.

Disappearing post demonstration

Ball Lifter

Most early pinball machines required the player to manually lift the ball from inside the cabinet into the shooter lane where it would be shot onto the playfield with the plunger.  In the 1960s the ball lifter was replaced by an automated kicker powered with a solenoid.

Ball Lifter Ball Lifter instruction card

When the lower plunger is pushed in, a lever swings up that carries the ball above the playfield and into the shooter lane as shown in the following video.  In this demonstration the ball falls below the playfield as soon as it is launched.  In a real pinball machine the ball would be routed back to the ball lifter from the drain between the flippers and from any other hole where the player might lose the pinball.

Ball lifter demonstration


Large electromagnets like this were used in some games to change the path of the ball without touching it from below the playfield.  Electromagnets have no effect unless they're powered so turning them on and off can have interesting effects.

Electromagnet Electromagnet instruction card

When the electromagnet is powered, the ball is attracted to the center of the electromagnet.  If the electromagnet stays on the ball will oscillate around the center and eventually stop.  Powering the electromagnet intermittently on the other hand can accelerate the ball if done at the right times.

Electromagnet demonstration

For a more in depth explanation of why the ball in the video behaves as it does, visit the Electromagnets and Acceleration page.

Credit Unit

The Credit Unit keeps track of how many game credits the player has and is usually visible through a small window in the backglass.  Coins and replays increase the total while each new game decreases the total.  The credit unit is a form of stepper unit that can step both forward and backward one step at a time.

Credit Unit Credit Unit instruction card

The video below demonstrates the mechanism that limits the credit unit to one step at a time in either direction.  This is done with mechanical lever arms activated by the increment and decrement solenoids.

It also reveals how the credit unit is electrically limited to a range of values (e.g. zero to 14 credits in this case).  The video frame below shows two pins mounted to the dark grey gear which rotates to reflect the number of game credits.  When there are zero credits remaining, the pin on left opens the two switches in the upper left corner to cut power to the decrement solenoid of the credit unit and to the new game circuit.  In this state the credit unit will only allow the player to increment the credit count by winning a replay or depositing a coin.

Similarly, when a maximum number of credits is reached, the other pin (at the bottom of the frame below) opens the third switch which disables the increment solenoid of the credit unit.  This prevents the credit unit from over winding.

Credit unit demonstration

Ball Count Unit

The Ball Count Unit keeps track of how many balls the player has played.  Lights wired to the Ball Count unit usually indicate the ball in play.  The Ball Count Unit is another form of stepper that can step forward one step at a time or reset back to the beginning.  It cannot decrement by one step like the Credit Unit above.

Ball Count Unit Ball Count Unit instruction card

In the video below the larger solenoid is used to advance the gear and contact fingers one step at a time.  The smaller relay just lifts a catch out of the way allowing a spring to reset the gear to the starting position.

Ball count unit demonstration

Stepper Unit

Stepper units are used to track features that step through a sequence as the game is played.  For example the game might have several features that light up one at a time in order.  This stepper is similar to the Score Reels above because it advances one step at a time, in one direction only.  It differs from the Credit Unit and Ball Count Unit above because it can only advance; it cannot decrement or reset.

Stepper Unit Stepper Unit instruction card

In the video below the stepper is paired with an orphaned light board from an unknown game to show how the stepper can be wired to step through a sequence of lights.  The video also shows some closeups of the ratcheting and rotating contacts.

Non resetting stepper demonstration

Score Motor

The Score Motor is the heartbeat of the pinball machine.  It rotates periodically during the game when sequences of events need to happen in a specific order.  As the motor turns cams open and close switches in a specific, repeatable order similar to the way the drum in a music box plucks the fingers that play the tune.

The first time the Score Motor runs is when a new game starts.  All the features need to be reset, score reels returned to zero and the first ball kicked out to the shooter lane.  During the game the Score Motor might run to score 50 points (advancing the 10s score reel five times) when a single switch closes for example.

This score motor is from a D. Gottlieb & Co. pinball machine and is wired to a set of score reels to show how scoring five points might work:

Gottlieb Motor with attached score reels Gottlieb Motor instruction card

The video below demonstrates the D. Gottlieb & Co. score motor which uses two cams and a set of pins mounted to the cams to open and close the switches.  The video also demonstrates how the switches operate according to the Motor Sequence Chart shown in the instruction card above and often found on the schematic diagram of a D. Gottlieb & Co pinball machine.

Gottlieb score motor demonstration

This score motor is from a pinball machine made by Williams Electronic Manufacturing Company and uses a set of cams but no pins to operate the switches.  A switch from each cam is used to light one of the bulbs in front to show the timing of the various cams.

Williams Score Motor Williams Score Motor instruction card

The following video demonstrates the Williams Electronics score motor.

Williams score motor demonstration

Captive Ball Unit

The Captive Ball Unit was a feature in the backbox of a few games that would fire a ball vertically through a pachinko-like maze and award points based on which lane the ball ultimately fell through.  The player had no control over the ball in the captive ball unit.  It was just a fun diversion from what was going on on the playfield.

Captive_Ball_UnitCaptive Ball Unit Captive Ball Unit instruction card

The lights near the bottom were added to highlight which lane the ball falls through as was the bell that rings when the ball drains through the middle lane.

Captive ball demonstration

Projection Unit

The Projection Unit was used to project the available game credits onto a frosted window on the backglass.  Light from a bright bulb on the back of the unit shines through a pin hole, through the printed wheel, and through a focusing lens before reaching the glass.  On this board the backglass is represented by a small piece of plastic held in a tube in front of the Projection Unit lens so the projection can be seen.

A predecessor to the Credit Unit above, the Projection Unit was used in some games until the late 1940s.

Projection Unit Projection Unit instruction card

The video below shows how the bulb, pin hole and lens project a number from the printed wheel onto the frosted plastic window.  Note that the numbers on the wheel and behind the lens are upside down to appear correctly after the image passes through the focusing lens.

Projection unit demonstration

Spin Unit

The Spin Unit is a clever way for the game to randomly change a game feature.  Ordinarily steppers can only increment, decrement or reset.  The Spin Unit is able to randomly change from any position to any other position.  It does this by using a pair of steppers.  The first, larger stepper is configured like a Ball Count Unit; it steps up one step at a time and can reset back to its starting position.  During a game this stepper advances periodically as certain targets are hit or switches close.  It also resets periodically when other targets are hit.

As the first stepper resets, the teardrop shaped board attached to its axle rotates and kicks the white spinner mounted above it.  The spinner spins for an indeterminate number of revolutions, closing a switch once for each revolution.  (The spinner mechanism is usually used on the playfield as a target that rewards points for each revolution.)

Each time the switch on the spinner closes, it sends a pulse to the second, smaller stepper which is configured as a simple Stepper (with no decrement or reset).  While the second stepper does advance a single step at a time, it advances a step for each revolution of the spinner which effectively randomizes its final resting position.

The number of steps the second stepper takes is loosely correlated to the number of steps the first stepper took before it kicked the spinner because each step on the first stepper winds its spring a little tighter and will make it kick the spinner a little harder.

Spin Unit Spin Unit instruction card

The video below demonstrates how the smaller stepper can be advanced randomly with the large stepper/spinner assembly or just manually with the extra button.  You might also notice that the large stepper has a limit switch on the back side that opens to prevent the stepper from over winding the spring.

Spin unit demonstration