Pinball
Solenoids

Flipper solenoids contain two coil windings in one package; a short, heavy gage 'power' winding to give the flipper its initial thrust up, and a long, light gage 'hold' winding that uses lower power (and creates far less heat) and essentially just holds the flipper up allowing the player to capture the ball in the inlane for more precise aiming. As the flipper nears the end of its upward travel, a switch under the flipper disconnects the power-winding and leaves only the second sustain winding to hold the flipper up in place. If this switch fails 'open' the flipper will be too weak to be usable, since only the weak winding is available. If it fails 'closed' the coil will overheat and destroy itself, since both windings will hold the flipper at the top of its stroke.

Solenoids also control pop-bumpers, kickbacks, drop target resets, and many other features on the machine. These solenoid coils contain a single coil winding. The plunger size and wire gage & length are matched to the strength required for each coil to do its work, so some types are repeated throughout the game, some are not.

All solenoids and coils used on microprocessor games include a special reverse-biased diode to eliminate a high-voltage pulse of reverse EMF (electromotive force). Without this diode, when the solenoid is de-energized, the magnetic field that was built up in the coil collapses and generates a brief, high-voltage pulse backward into the wiring, capable of destroying the solid-state components used to control the solenoid. Proper wiring polarity must be retained during coil replacement or this diode will act as a dead short, immediately destroying electronic switches. Older electromechanical AC game solenoids do not require this diode, since they were controlled with mechanical switches. However, electromechanical games running on DC do require diodes to protect the rectifier.

All but very old games use low DC voltages to power the solenoids and electronics (or relays). Some microprocessor games use high voltages (potentially hazardous) for the score displays. Very early games used low-voltage AC power for solenoids, requiring fewer components, but AC is less efficient for powering solenoids, causing heavier wiring and slower performance. For locations that suffer from low AC wall outlet voltage, additional taps may be provided on the AC transformer in electromechanical games to permit raising the game's DC voltage levels, thus strengthening the solenoids. Microprocessor games have electronic power supplies that automatically compensate for inaccurate AC supply voltages.

Historically, pinball machines have employed a central fixed I/O board connected to the primary CPU controlled by a custom microcontroller platform running an in-house operating system. For a variety of reasons that include thermal flow, reliability, vibration reduction and serviceability, I/O electronics have been located in the upper backbox of the game, requiring significant custom wiring harnesses to connect the central I/O board to the playfield devices.

A typical pinball machine I/O mix includes 16 to 24 outputs for driving solenoids, motors, electromagnets and other mechanical devices in the game. These devices can draw up to 500 W momentarily and operate at voltages up to 50 Vdc. There is also individually controlled lighting that consists of 64 to 96 individually addressable lights. Recently developed games have switched from incandescent bulbs to LEDs. And there is general illumination lighting that comprises two or more higher-power light strings connected and controlled in parallel for providing broad illumination to the playfield and backbox artwork. Additionally, 12 to 24 high-impulse lighting outputs, traditionally incandescent but now LED, provide flash effects within the game. Traditionally, these were often controlled by solenoid-level drivers.

A game typically includes 64 to 96 TTL-level inputs from a variety of sensors such as mechanical leaf switches, optical sensors and electromagnetic sensors. Occasionally extra signal conditioning is necessary to adapt custom sensors, such as eddy sensors, to the system TTL inputs.

Recently, some pinball manufacturers have replaced some of the discrete control wiring with standard communication buses. In one case, the pinball control system might include a custom embedded network node bus, a custom embedded Linux-based software stack, and a 48-V embedded power distribution system.
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