Since opening as a temporary museum in 1949, the Oregon Museum of Science and Industry has hosted countless exhibits, both stationary and traveling. Traveling exhibits varying in subject matter and size, take wondrous, interactive experiences to five continents, twenty-three countries, and 1240+ clients.
One such exhibition is Mindbender Mansion. Six years after it originally debuted in 2008, OMSI decided to recreate the popular exhibit and contracted Thomas Hudson to design and fabricate electronics for four of the interactive features- the Tilt Table, Spelling Fever, Feeding Frenzy, and Sensing Squares. In this post, he shares a behind the scenes look at what went into the creation of the Tilt Table and Spelling Fever.
The Tilt Table
The Tilt Table is a fun take on a pinball machine. Rather than pulling a plunger or tapping buttons and using flippers, players manually move the table to score points by dropping the ball in goals.
Each of the seven goals has a ball ejector consisting of a simple coil that jettisons a metal rod into the ball. These are sourced through pinball distributors, and are powered by a ~40 volt power supply from Digi-Key. Thomas and his team used relays to convert a 5V signal to send ~40V to the coils for a fraction of a second, which triggers the metal rod to eject the ball.
Sparkfun’s infrared emitters/receivers were used to create a pinball sensor. An IR beam is projected through a plexiglass tube. When the pinball is present, it breaks the beam and introduces as analog signal into the uController. If necessary, they could be then be tuned appropriately. Mounting the sensors under the table mitigated most of the IR interference from the sun or other light sources. This resulted in very little need for tuning the sensors, and typically a flawless operation.
In keeping with the feel of a traditional pinball experience, their team wanted to provide the typical sound effects players would expect. To accomplish this, they used an audio shield with SD card on the Teensy3.1 uController, and filled the SD card with all the usual pings and whistles.
Since the Teensy requires 3.3 volts, they used two level shifters to communicate between 3.3 and the 5 volts necessary for lighting effects and operation of the timer/ scoreboard. A 14-dip, 74AHCT125 level shifter controlled the WS2812 RGB LED rings from Adafruit. These created attractor LED patterns around each hole that changed to a solid once the goal was made. The other level shifter, a simple mosfet design from Sparkfun, facilitated I2C to the timer and scoreboard. Both shifters are visible on the white protoboard above.
The scoreboard and timer displays are visible on either side of the table. These are Adafruit’s 0.56” Seven Segment displays.
Spelling Fever poses questions to the participants, which they answer by stepping on a combination of letters and safe squares out of an array of 128. Click here to see it in action!
One of the genius bits of mechanics utilized in the 2008 exhibit was the step-on button. After the button is fully depressed, any additional pressure is absorbed by springs. A button is mounted with each letter in in a lightbox. The letters are backlit by four LEDs mounted facing downwards, diffusing the light and reflecting it off an aluminum plate.
The LEDs were wired in parallel at 2.25 volts, consuming about ½ amp and heating up the aluminum a little. To decrease the heat and runtime for the LEDs, they used an ‘attractor pattern’ when no one was using the exhibit.
For ease of transport, letters were divided into banks that can be disconnected for shipping. Each bank consists of 32 letters. Each bank of letters connect to a master controller over I2C.
Four shift-in registers shift IN all the inputs from the buttons stepped on. Four shift-out registers shift-out to mosfets that trigger the LED lights ON and OFF. These parts are on a large shield above that fit over an Arduino.
Thomas Hudson’s website
More about Mindbender Mansion on OMSI’s official website
*This post was originally co-written by Thomas Hudson and myself for OSH Park’s blog.