“The future depends on what you do today.”
Gandhi
Weightbearing platform & laser gun
This interactive therapeutic system is designed to promote correct standing alignment through play. The idea is that Julian maintain proper bilateral weight distribution; and when adequate symmetry is achieved, the system wirelessly activates a laser gun. If asymmetrical posture is detected, the gun is disabled until corrective adjustment is made.
The system has three core components: a pressure-sensitive standing platform, a wirelessly controlled laser gun, and a target.
Platform
The platform monitors Julian’s bilateral weight distribution by measuring plantar pressure using 8 integrated force sensors. Proper standing posture is defined as a near-equal load between the left and right lower limbs. The platform has a user-definable tolerance value to accommodate natural postural sway.
Structurally, the platform consists of two sliding, independently mounted foot panels, each embedded with four high-capacity pressure sensors positioned at the forefoot and heel regions. These sensors continuously measure the relative load symmetry between both feet.
The system compares the output from each sensor group on one foot with the corresponding group on the opposite foot. If the computed deviation falls within a user-defined acceptable variance threshold, the platform wirelessly enables the laser gun.
To accommodate individual variability in postural control, the platform features a hardware-based tolerance adjustment dial. This dial modulates the allowable inter-limb pressure difference, ranging from 10% (strictest setting) to 50% (most lenient). For example, at the 50% setting, a pressure group on one foot can register up to twice the load of its counterpart and still be considered “balanced.”
Only when the real-time weight distribution remains within the selected threshold does the system wirelessly trigger the activation circuit of the laser gun.
Wireless communication between the platform and the laser gun is with two Series 2 XBee modules operating in a unidirectional configuration. In the current implementation of the Laser Gun Game, the platform acts as the transmitter, periodically sending activation signals to the laser gun upon validation of correct posture.
Laser gun
Much to the boys’ dismay, I gutted the mechanism of a Nerf Mega Blaster. My main concern was safety, so the gun's electronics incorporates three core safety features to ensure safe operation. These are:
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The laser gun is always OFF unless the platform activates it.
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There is a motion detector in front of the platform which turns the laser off when motion between the target and the platform/laser is detected.
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On startup, the gun is calibrated to turn off the laser if the gun itself turns away from the target. This is achieved by an ultrasonic proximity sensor in the gun, which measures the distance to the target. Since the size of the target is known, the gun calculates the hypotenuse of the distance to the target. From that point on when the ultrasound sensor measures any distance greater than that initial hypotenuse value the laser is deactivated. However, as he is much shorter in size than the distance to the target there is also an accelerometer in the gun which deactivates the laser if the gun’s acceptable angle downwards is exceeded
Using the laser gun
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The gun is switched on and pointed at the centre of target for calibration.
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The ultrasonic proximity sensor determines distance (A) to target.
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B is calculated using the Pythagorean Theorem
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From this point forth, if the ultrasound sensor reads a distance to the wall of greater than B (e.g. C), the laser is deactivated.
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At the same time as the ultrasound distance (A) is determined in #2 above. The accelerometer also sets its X axis of alignment to 0 degrees.
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The accelerometer continuously checks the angle down and if it exceeds 30 degrees the laser is deactivated.
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The laser will be activated ONLY when all four of the following conditions are met:
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Platform sends okay-to-shoot signal to gun
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The distance to wall is less or equal to original calculated hypotenuse value
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The angle of gun is >-30 degrees.
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There is no motion in front of platform
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Laser gun components
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3 X AAsLaserGunParts
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On/Off
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USB access
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Arduino Uno Rev3 / Sparkfun Xbee shield / XBee series 2
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Momentary switch for trigger (toggle on off)
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LED to indicate okay to shoot
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Accelerometer
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Mess of wires
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Speaker
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Red laser
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Ultrasound sensor
Target
The first prototype of the target system is a stationary square panel controlled by an Arduino Mega 2560 microcontroller. It incorporates 15 LEDs, each paired with a corresponding photoresistor for light detection. The user’s score is output to a blue 4-digit 7-segment display, which initializes to zero upon system startup.
During operation, LEDs are randomly activated for 3 seconds. If the corresponding photoresistor detects a significant increase in light intensity within this window—indicating a successful hit—the system increments the score and updates the display in real time.
Future iterations of the design will integrate moving mechanical elements driven by two servo motors and a stepper motor, enabling dynamic repositioning of target components. The random() function will be used to activate specific targets, each potentially assigned distinct score values to enhance gameplay enjoyment.
