1. Internal Luggage Scale
Team 40
Ryan Owan, Shivani Mouleeswaran, Jonathan Li
ECE 445 Senior Design
Fall 2018

2. Overweight Luggage Problem
50 lbs
Avg. max weight for checked-in luggage
$4.6 billion
2017 U.S. airline profits from overweight fees $
Avg. overweight fee per passenger
Shivani

3. 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

4. The Suitcase Yellow: LCD Blue: PCB with microcontroller Red: battery
Orange: load cells
ryan

5. High-level Design Specifications1
+/- 1 pound accuracy
Real-time convenience
< 7 lbs added weight
Maximize packable items 2
TSA approved
Carry on or check in 3
Jonathan

6. Block Diagram NiMh battery passes airline regulations (LIon does not )
Jonathan

7. 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

8. Voltage regulator output
Ryan

9. User Interface Purpose Display weight to tenths place
Real-time updates
Components
2x16 LCD Display
I2C Communication
Jonathan

10. I2C Waveform
Jonathan

11. Control Unit Purpose Interface between hardware components
Analog-to-digital conversion
Numerical weight conversion
Components
Atmega-328P microcontroller
Jonathan

12. Weight Module Purpose Generate analog signal proportional to weight
Components
Four 50 kg load sensors
INA114P instrumentation amplifier
Jonathan

13. Load Cell Single contact point on top Resistive properties
Compression changes resistance value
Very small output - requires amplification
Jonathan

14. Wheatstone bridge
Shivani

15. Load cell factors & equations
Rated load: 50 kg
Rated output: 1 mv/V
Operating voltage: 5 VDC
Shivani

16. 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

17. Mechanical design
Plexiglass vs Polycarbonate
Rigidness vs Weight
Ryan

18. Cell Covering High pressure on contact point
Cover distributes weight more evenly
Ryan

19. Results: Testing smaller scale
25% actual size
Weights ranging kg
20 samples averaged per output
Shivani

20. Results: Testing full-size scale
Scale sets to zero on power-up
High variability in readings
200 samples averaged per output
Shivani

21. Results: Sources of error
Incorrect load cell rating
Loose connection between load cells
Flexible plates = uneven weight distribution
Uneven pressure on contact point
Ryan

22. Future work Improving weight reading accuracy
Improving mechanical designs
Full system integration
Ryan

23. Questions?