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

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

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

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

Dynamo 6V, 3W AC output

Dynamo

Rectifier Diode bridge full-wave rectifier 100μF smoothing capacitor

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

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

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

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

Hall Effect Sensor Testing Tested with a treadmill Actual Speed Measured Speed Max Error 0.5 mph 0.4 - 0.6 mph 20% 1 mph 0.9 - 1.2 mph 1.5 mph 1.4 - 1.7 mph 13% 2 mph 1.9 - 2.3 mph 15% 4 mph 3.9 - 4.2 mph 5% 6 mph 5.8 - 6.2 mph 3%

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

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

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

Display Low-power LCD display 128x64 pixels 55x46 mm 4-wire SPI interface Data written in 1x8 bit columns Angular size of text: 0.011 rad 0.008 for average computer display

Display Mockup

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

Real-World Picture

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