AVR Bicycle

Features

• Speedometer
• Distance traveled
• Battery status
• Back and front direction signalization
• Back red light with multiple patterns to pick from
• Main front lamp control
• Runs on 16.4V (2x serial Li-Ion battery pack) battery managment system (BMS) included

Requirements

• 1 digital pin to measure velocity and distance, pin will be used as counter
• 1 ADC pin for battery status
• 2 digital pins for front and back direction signalization light control
• 6 digital pins for the back red light control
• 1 digital pin for main front light control
• 1 digital pin for front light control
• 2 (SCL and SDA) pins for display (with Vcc and GND)
• 4 digital pins for buttons

Total: 17 digital pins and 1 ADC pin

Calculations

Speedometer

• Distance of sensor and magnet from center of front wheel is 10cm (100mm | 0.1m)
• Perimeter is then 2 π 0.1m = 0.628m
• Minimum velocity thant can be measured is 1km/h (1km/h / 3.6 = 0.277m/s)
• Maximum velocity thant can be measured is 178.5km/h (178.5km/h / 3.6 = 49.583m/s)
• Uses 8bit Timer/Counter2 to count the number of revolutions per second

Velocity	Period	Frequency
1km/h	2.257s	0.441Hz
100km/h	22.677ms	44.1Hz
178.5km/h	8.226ms	121.5Hz

v = (distance / dt)[m/s] * 3.6 [km/h]

we take average of all distances and divide by dt, dt will be 1 second, we multiply by 3.6 to get km/h

Distance meter

• User is required to set wheel radius
• Uses 8bit Timer/Counter2 to count the number of revolutions per second and multiply it by perimeter of the wheel

Example with 16inch (R = 0.4064m) wheel, r = 0.4064m / 2 = 0.2032m

• Perimeter of wheel is 2 * π * 0.2032m = 1.276m
• Each turn of wheel bicycle has moved 1.276m
• Wheel has turned 5 times in 1 second, so distance traveled that second is; 5 * 1.276 = 6.38m

Battery Status

• Maximum battery voltage = 16.8V
• Minimum battery voltage = 12.0V

VREF is ~ 5.0V so to get voltage at ADC to be 5V when battery is at maximum we need voltage divider
with ratio of 5.0V / 16.8V = 0.297

R1 = 23_600 Ω
R2 = 10_000 Ω
R2 / (R1 + R2) = 10kΩ / (10kΩ + 23.600kΩ) = 0.297

Beginners note:
There is no 23_600kΩ available so it will need to be a series of:
22kΩ + 1kΩ + 680Ω = 23.680kΩ

And so at minimum battery voltage we read at ADC value of 12.0V * 0.297 = 3.564V
Resolution of 8bit ADC is 5 / 255 = 19.607mV, so binary value is 3.564V * 19.607mV = 181.771 or 181

Battery Voltage	ADC value	Status
>16.8V	>181	Over Charged
16.8V	181	Full
12.0V	107	Discharged
<12.0V	<107	Over Discharge

Directional signalization

2 pins control 2 sets of yellow diodes, for left and right side

Display

Displays velocity,distance traveled,battery status.

Menu

• Select velocity unit m/s or km/h
• Select wheel radius (16inch, 18inch, 19.5inch etc)
• Reset distance

Buttons

• Button for front light on/off, long press shows/hides main menu
• Button for left turn signalization, toggle on press
• Button for right turn signalization, toggle on press
• Button for backlight, long press turns it on/off, short changes effects