Internal Luggage Scale Team 40 Ryan Owan, Shivani Mouleeswaran, Jonathan Li ECE 445 Senior Design Fall 2018
Overweight Luggage Problem 50 lbs Avg. max weight for checked-in luggage $4.6 billion 2017 U.S. airline profits from overweight fees $100-200 Avg. overweight fee per passenger Shivani
Excess physical exertion No time/space to repack = fees Current Solutions Bathroom scale 01 Can only be used at home Portable luggage scale 02 Excess physical exertion Airport scale 03 No time/space to repack = fees Ryan
The Suitcase Yellow: LCD Blue: PCB with microcontroller Red: battery Orange: load cells ryan
High-level Design Specifications 1 +/- 1 pound accuracy Real-time convenience < 7 lbs added weight Maximize packable items 2 TSA approved Carry on or check in 3 Jonathan
Block Diagram NiMh battery passes airline regulations (LIon does not ) Jonathan
Power Subsystem Purpose Regulate supply to 5V Consistent power for min. 2 hours Turn power on/off Can be recharged Components NiMh charger NiMh battery Power switch Voltage regulator Ryan
Voltage regulator output Ryan
User Interface Purpose Display weight to tenths place Real-time updates Components 2x16 LCD Display I2C Communication Jonathan
I2C Waveform Jonathan
Control Unit Purpose Interface between hardware components Analog-to-digital conversion Numerical weight conversion Components Atmega-328P microcontroller Jonathan
Weight Module Purpose Generate analog signal proportional to weight Components Four 50 kg load sensors INA114P instrumentation amplifier Jonathan
Load Cell Single contact point on top Resistive properties Compression changes resistance value Very small output - requires amplification Jonathan
Wheatstone bridge Shivani
Load cell factors & equations Rated load: 50 kg Rated output: 1 mv/V Operating voltage: 5 VDC Shivani
Factors affecting load cell output Amplification Increase signal for microcontroller to read Orientation & stability Evenly spaced & rigidly mounted Distribution Even weight distribution across sensors Shivani
Mechanical design Plexiglass vs Polycarbonate Rigidness vs Weight Ryan
Cell Covering High pressure on contact point Cover distributes weight more evenly Ryan
Results: Testing smaller scale 25% actual size Weights ranging 0 - 1 kg 20 samples averaged per output Shivani
Results: Testing full-size scale Scale sets to zero on power-up High variability in readings 200 samples averaged per output Shivani
Results: Sources of error Incorrect load cell rating Loose connection between load cells Flexible plates = uneven weight distribution Uneven pressure on contact point Ryan
Future work Improving weight reading accuracy Improving mechanical designs Full system integration Ryan
Questions?