The Concept
In the Zeus versus Poseidon game, the wall sensor is the players' means to have more balls dispensed. Normally, the sensors are blue for Poseidon, but are randomly illuminated bright yellow for Zeus. If the players touch the panel while it is lit in Zeus's colors, additional balls are dispensed so that they can be shot at the moving targets in the game. If balls hit the targets, players accumulate points; the game is a race to score the maximum number of points in the allocated time.
The Physical Implementation
The key mechanical constraint on the implementation of the button is the robustness to wear from players. In order to survive the large impulses that players will exert on the button, and also to ensure that the button does not fail from fatigue over thousands of play cycles, it features no mechanical actuation. Instead, a force sensitive resistor is constrained between the aluminum backplate and the front panel. This force sensitive resistor has been validated to have less than 5% functionality change over 1 million 1kg force cycles, and can support up to 31kN without damage. The sensor is able to resolve forces as small as 0.2N, ensuring that players do not need to exert excessive force to activate the panel.
The design features a machined aluminum backplate. This backplate has been designed such that all the milling can be accomplished with a single, 1/4" end mill. The design features two sets of M6 bolt holes - one set at the corners allows the front plate to be bolted on, while the other at the ordinal positions allows it to be mounted. The backplate also features a pocket to house the circuitry for the device. At the bottom of the housing, an LED strip with 6 RGBW LEDs uniformly illuminates a diffusive acryclic sheet from below. This concept works similarly to a computer monitor, as light entering the acrylic at the bottom passes through a highly diffusive material and is projected out the front of the device. The sheet is masked to feature a tranlucent projection of a lightning bolt for Zeus. The force sensitive resistor is mounted between the acrylic and backplate freely, and pressure is not applied by the acrylic as it rests in the housing. A front plate is bounted onto the housing to constrain the acrylic.
The Electrical Implementation
The module is powered through a 12V power supply. The LED strip requires 60mA for each LED, and thus requires 360mA for 6 LEDS. The color of the LEDs is controlled through a microcontroller-controlled PWM voltage of each of the RGB channels. This voltage drives an n-channel MOSFET for each of the 3 channels which effectively acts as a variable resistance between the supply and ground. By applying the correct voltages to these three channels, a uniform, bright LED light of any hue can be commanded. Normally, this light is blue to indicate Poseidon's control, but will illuminate to yellow to indicate to the player's that it is under Zeus's control and will provide a ball when pressed. If pressed correctly, the system will output green light to provide user feedback of a correct response. If the button is pressed while blue, it will turn red to indicate incorrect response.
The force sensitive resistor forms a very simple voltage divider circuit which produces a microcontroller readable analog voltage depending on whether or not the button is depressed. The system requires a 5V regulated supply which is provided through a linear regulator fed by the 12V input voltage. Given the very low current required for this application, the simplicity of the regulator makes it a superior option to power electronics or more complicated circuitry to produce this voltage. A pull-down resistor ties the analog microcontroller pin to ground and completes the voltage divider.