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Dick Hamill edited this page Aug 3, 2020 · 3 revisions

Stars 2020

An Update to a Classic Stern Pinball Machine

Manufactured in 1978, Stars was one of Sterns first solid state pinball machines. It was the first machine designed by Steve Kirk, and contains a post between the flippers that came to be known as the “Kirk Post.”

The code for Stars was contained in two 2k PROM chips, like many machines of that era. The goals were simple—light the stars and collect the bounty on the right spinner. The drop targets granted the player bonus multipliers, an extra ball, and a special.

The purpose of this project is to update the rules of Stars and re-use as much of the original hardware as possible in the project. A secondary goal is to spend as little money as possible. There’s a third goal of the project that is based in pettiness and revenge, so we won’t talk of it here.

To achieve those goals, this project replaces the M6800 processor in socket U9 with a daughter board connected to J5 on the MPU. That daughter board contains only an Arduino Nano (single board controller), some wires, and connectors. The new code base takes up nearly 30k of space on the Arduino, so it’s nearly seven times as interesting as the old code.

The new features include:

  • Multiple brightness levels for the lamps
  • Flashing scores when the playfield hasn’t yet been validated
  • A skill shot
  • Three levels of star collects
  • A tally of pop bumper hits that grants rewards at different levels
  • A ball save feature
  • A “wizard mode” for players who achieve the main goals
  • Scoring up to 4 billion

Because this implementation only addresses the PIA chips on the MPU board, it eliminates the need for the PROM, RAM, and cRAM chips at U2, U6, U7, and U8. Because of this, MPU boards with damaged chips or sockets at those locations can still be used. This implementation also uses the EEPROM on the Arduino to store the high score, credits, and audit values, so a battery on the MPU is also not required.

With the addition of a 74LS125 (line buffer), the Arduino can be "dual-booted" with the original M6800.

This project uses the base library called BallySternOS. To learn how to build the hardware for this project, head over to the hardware section on the BallySternOS repository. Read on for descriptions of:

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