1. Group 60 ECE 445 Spring 2016 Devin Berchtold Michael Yu
Longboard-o-Meter
Group 60
ECE 445 Spring 2016
Devin Berchtold
Michael Yu

2. Introduction Display speed, incline, and calories to longboard rider
Safe and convenient
Battery powered
Device using sensors to gather data and output meaningful data to display

3. Objectives and Motivation
Recharges itself
Safer than a phone app
More accurate than a phone app
Safety is important. Useful when going high speeds.

4. Block Diagram Power 6V Dynamo Rectifier POW31944M 6V Charging Circuit
Key
Power (DC)
Power (AC)
Data (1 bit)
Data (4 bit SPI) 6V
Battery
RC-DA5HPHTx2 6V 4V
3.1V
Voltage Regulators 2V
Hall effect sensor
55100
Microcontroller
ATmega328
Display
EA DOGM128-6
Gyroscope
L2G2IS

5. Dynamo
6V, 3W
AC output

6. Dynamo

7. Rectifier
Diode bridge full-wave rectifier
100μF smoothing capacitor

8. Charging Circuit and Battery
Charging circuit regulates current
R = 0.6 / Charging current
6V Ni-Cd 1400mAh
Slow charge rate of C/10 = 140mA

9. Voltage Regulators 6V DC input 2V regulator 3.1V regulator
2.013V output
3.1V regulator
3.114V output
4V regulator
3.970V output

10. Hall Effect Sensor Count revolutions of the wheel to measure speed
Uses a magnet attached to the wheel and a magnetic sensor
Sensor voltage switches when magnet is within 25 mm

11. Hall Effect Sensor Calculations
Speed
Sample Time
Calculate running average over six 0.4-second intervals (2.4 seconds total) for desired accuracy

12. Hall Effect Sensor Testing
Tested with a treadmill
Actual Speed
Measured Speed
Max Error
0.5 mph
mph
20%
1 mph
mph
1.5 mph
mph
13%
2 mph
mph
15%
4 mph
mph 5%
6 mph
mph 3%

13. Calorie Calculation Calories burned increases linearly with heart rate
Constants calculated with experimental testing
Ride at various speeds and inclines, find constants such that:
MET ≈ 8 when heart rate is maximized
MET ≈ 3 when riding at a leisurely pace

14. Microcontroller ATmega328 Updates every 0.4 seconds
Watches hall effect sensor to count wheel revolutions
Connected to analog pin of microcontroller
Increments whenever input voltage goes to zero
Reads incline data from gyroscope
4-bit SPI
Calculates speed from revolution count
Calculates calorie count
Writes data to display

15. Software Flowchart Start Reset Gyroscope Initialize Display
Reset Timer
and Counter
Send Data
to Display
Increment Counter
Start Gyroscope
Measurement
Format Data
for Display
Yes
Timer Done?
Hall
Effect
Sensor
Switched? No
Yes
Read Data from Gyroscope
Calculate Speed and Calories No

16. Display Low-power LCD display 128x64 pixels 55x46 mm
4-wire SPI interface
Data written in 1x8 bit columns
Angular size of text: rad
0.008 for average computer display

17. Display Mockup

18. Challenges Gyroscope was too small to solder
Get gyroscope with pins, or a header
Hall effect sensor misses revolutions at high speeds
Adjust revolution counting code
Display is dark when soldered to PCB
Check capacitors and connections
Dynamo broke above 10 mph
Order a better one

19. Real-World Picture

20. Conclusion Possible Improvements Configurable interface
Improve accuracy
More compact device
Easier Installation
Weather resistant