1. Bike Buddy Group 15 Sponsored By: Ari Nacius Progress Energy
Nowook Park
Ethan Pemble
Nick Quinlan

2. Introduction [picture]
Speed: 18 MPH
Dir:28.53˚N, ˚W
T:85 ˚F P=4.2W
Bike Buddy uses a portable AC generator to harness power from pedaling.
It attaches to the bicycle and displays riding information.
Speed (mph) and direction
Lat./Long. coordinates
Ambient temperature
Power generated by pedaling (Watts)
It also supplies power to USB devices.
[picture]

3. Goals & Motivation
Current portable bicycle generators are primarily used to power headlights.
Our goal is to expand on possible applications of this alternative energy source by providing additional features to the bike rider.
Provide accurate data to the user while efficiently powering all systems with the AC generator.

4. Power Flow Diagram Power System Display System AC generator
Pedal the bike
DC converter
Battery switcher
Battery charger
6v regulator
5v regulator
3.3v regulator
Display System
USB µC
GPS
LCD

5. Bike Buddy Power System

6. Specifications & Requirements
Power
Peripheral
Operating voltage
Expected maximum current draw
Power requirement
Microcontroller
3.3v
19 mA
62.7 mW
LCD 6v
220 mA
1320 mW
GPS
70 mA
231 mW
USB port 5v
500 mA
2500 mW
Total Power
4.12 W

7. Building the Generator
Initially we wanted to design our own custom generator.
Instead of spending time on designing a generator we decided to concentrate on the capabilities of the LCD and sensing functions.
Because it was vital to provide constant power for the rest of the project to work, we thought it best to purchase one instead.
Example of a home-made electric generator

8. Choosing a Generator Pros: Higher Power Output Cheap Cons:
Less energy loss to friction
Sleek design
Cons:
More expensive
Custom Wheel Needed
Low Power Output
Pros:
Higher Power Output
Cheap
Cons:
Energy Loss in wet or muddy conditions
Produces buzzing noise
Voltage
(volts)
Current
(milliamps)
Power
(watts)
Cost
(USD)
Current Source 6V
400mA
2.4W
$63.70 AC
Voltage
(V)
Current
(mA)
Power
(W)
Cost
(USD)
Current Source
12V
500mA 6W
$16.99 AC

9. Power Supply AC/DC conversion Formulas to find the average DC
No need for a step-up or step-down transformer.
Full Bridge rectifier using 4 schottky diodes for low voltage drops.
A 50V 2200 uF electrolytic capacitor is used to minimize the ripple before regulation.
A voltage regulator (LM317) regulates the voltage to a constant 10V.
Formulas to find the average DC
Voltage from the generator ,
When Vrms = 30V,
Vdc = (30V x 1.414)/3.14 = 13.5V

10. Battery Characteristics
Lead Acid
Nickel Cadmium
Nickel Metal Hydride
Lithium Ion
Energy/Weight
(Wh/kg)
30-40
40-60
30-80
Energy/Size
(Wh/L)
60-75
50-150
Power/Weight (W/kg)
180
150
Charge/Discharge Efficiency
50-92%
70-90%
66%
80-90%
Energy/Price (Wh/USD) —
2.75
Self-discharge
Rate (per mo.)
3-20%
10%
30%
8% (21°C)
Cycle Durability
2,000
500-1,000
1,200
Nominal Cell
Voltage
2.105V
1.24V
1.2V
3.6V
Nominal Capacity
7200 mAh
900 mAh
700 mAh
4800 mAh
Size
151x98x98mm
73x29x52mm
51x48x22mm
127x80x43mm
Weight
3940g
210g
135g
678g

11. Specifications & Requirements
Lithium-Ion BatteryPack (2 Cell)
Capacity: 1400mAh
Voltage: 7.4 V (8.4 V pk)
Dimensions: 51mm x 38.1mm x 19mm
Weight: 2.5 oz
Maximum Charge Current: 1C or 1.4A
Maximum Current Draw: 0.87 A

12. Li-Ion Battery Charger
Charger Comparison Table
ADP (Analog Devices)
MAX1758 (Maxim)
MCP (Microchip)
Input Voltage
-0.4V to 18V
-0.3V to 30V
-0.3V - 12V
Max Charge Current
1.2A
1.5A 2A
Operational Temp
40C to +85C
Maximum Power Dissipation
500mW
762mW
120mW
Battery Temp monitoring No
Yes
Packaging
SO-8
SSOP-28
MSOP-8

13. Li-Ion Battery Charger
Typical Charge Profile
MCP73842 manufactured by Microchip to charge an 8.4V Li-Ion battery.
Programmable Charge Current.
Programmable Safety Charge Timers.
Preconditioning of Deeply Depleted Cells.
Automatic End-of-Charge Control.
Continuous Cell Temperature monitoring
Automatic power-down when input power is removed to prevent battery discharge.
Ctimer = 0.033uF
Tprecon = (Ctimer/0.1uF) X 1 hr = 19.8 mns
Tfast-charge = (Ctimer/0.1uF) X 1.5 hrs = 29.7 mns
Tterm = (Ctimer/0.1uF) X 3 hrs = 59.4 mns

14. Charge Circuit Flow Diagram

15. Li-Ion Battery Charger (cont’d)
For a maximum charge current of 2A, RSENSE is calculated using the formula in the datasheet.
RSENSE = 120mV / 2A = 60m
The charger turns off when the battery reaches a temperature limits of 10 F and 80 F.
Those temperature limits are set using two resistors Rt1 and Rt2
Rt1 = (2 x 10 x 100)/( ) = 22 Ohms
Rt2 = (2 x 10 x 100)/( x 10) = Ohms
Practical values:
Rt1 = Ohms
Rt2 = Ohms
*maufacturer-recommended design
configurationation.

16. Battery Switcher
2 comparators to monitor and compare the battery voltage levels with a reference voltage of 3.5V.
6 p-channel mosfets used to switch the batteries when the source battery reaches 3.5V.
A zener diode is used to keep the reference voltage at a constant 3.5V.
The 100uF capacitor is to ensure that the output doesn’t change during the switch.

17. Battery Switcher Switcher Profile
One battery powers the unit while the other is being charged.
Switch happens when the battery powering the unit reaches 3.5V.
3.5V is the minimum input voltage range of switching regulators that power the subsystems.
The power source switch does not affect the operation of the unit.
Switcher Profile

18. Switching Regulators Vref=1.5 V, 10kΩ ≤R1≤ 500kΩ R2=R1*(Vout/Vref-1)
For Vout=6V: R1=10kΩ,
R2=30kΩ

19. Switching Regulators
The MAX608 low-voltage step-up controller operates
from a 1.8V to 16.5V input voltage range.
Pulse-frequency-modulation (PFM) control provides high efficiency at heavy loads, while using only 85μA (typical) when operating with no load.
In addition, a logic-controlled shutdown mode reduces supply current to 2μA typical. The output voltage is factory-set at 5V or can be adjusted from 3V to 16.5V with an external voltage divider.
The MAX608 operates in “bootstrapped” mode only (with the chip supply, OUT, connected to the DC-DC output). The two bootstrap capacitors and are employed on both sides of inductor to provide gate voltage to high side input switch through high side driver in any mode of operation. This allows the regulator to work in all three modes of operation without different external components or configurations depending on the mode.

20. Bike Buddy Power Sensor

21. Current Sensor
The ACS756 current sensor needs a single +3 to+5V supply.
Ultra-low power loss: 130uOhm internal resistance.
13kVRMS isolation voltage between terminals 4/5 and pins 1/2/3.
Output voltage proportional to AC and DC current.
20mV/A output sensitivity.
Nearly Zero magnetic hysteresis

22. Analog-to-Digital Converter
The ADC pins have a voltage range of 0V to 5V. But since the internal reference voltage is 2.56V, our input voltage must not reach that level.
We use a voltage divider to prevent the attempted maximum voltage from the generator from reaching 2.56V on the ADC pins.
Voltage interval = 2.56V / 1023 = V
At every 2.5mV increment, a binary data is recorded and stored in a data register.
Since we want the recorded voltage to be accurate to 1/10 of a volt, we select resistor values that will increment the stored binary data at every 1/10 of a volt.
= (1/10)(R2/(R2+R1))
1/40 = R2/(R1+R2)
R1 = 39K, R2 = 1K

23. Analog-to-Digital Converter (cont’d)
The ADC is used to measure the power generated by the generator by monitoring the voltage and current.
The current sensor output is connected to a similar voltage divider as the one on the right for the battery.
Since we don’t want to drain the batteries, we use a to isolate the batteries from the voltage divider.

24. Bike Buddy Display System

25. Display System Goals NE Small and power efficient
Peripheral sensors to provide information to the rider:
Speed and direction
Power generated
Global position
Ambient temperature
Time of day
Lat:
12:37 PM
Lon:
67 °F NE
6.73 MPH
Generating 3.7 Watts µC
Power sensor
GPS

26. Liquid Crystal Display
Serial Graphic LCD from sparkfun
Provides simple 1-wire serial interface with built- in commands and character display.
128x64 pixel space
Software-scalable backlighting for indoor/outdoor use
Operates at 6v, average current draw ~125 mA (with full backlighting)

27. GPS Receiver: LS20031
The LS20031 GPS unit has an embedded antenna and simple TTL serial interface.
Built-in battery stores satellite positions for rapid startup.
41 mA

28. Microcontroller Atmel ATmega128 L Input/Output 53 pins Memory
128KB FLASH
4KB EEPROM
4KB internal SRAM
Analog-to-Digital
10 bit, 8 channel
Peripheral Interface
2 USART, TWI, SPI
Clock Speed
Up to 8 MHz
Operating Voltage
2.7 – 5.5 v
Expected Active Current
~20 mA

29. Development Board: STK-300
RS-232 port for USART communication.
Simple USB programmer for quick prototyping.
Provides 8 buttons and LEDs for testing.
External 8 MHz crystal provided for source clock.
Includes C compiler (WinAVR) and AVR Studio 4 development environment.

30. Software Overview Retrieve Sensor Data Initialize Serial Devices
Power Switch ON
Retrieve Sensor Data
Retrieve Power Sensor Data (ATD)
Retrieve GPS Data (USART1)
Retrieve Temperature Data
(TWI)
Format numbers for display
Update Display
(USART0)
Timer overflow?
Stand-by

31. ATmega128 Timer
The sensor update loop is driven by a timer, and executed every 300ms. The screen will update roughly 3 times per second.
Timer1: 16-bit timer
System clock rate: MHz
Prescaler: divide-by-1024
Tic: 7.2 kHz
Overflow: 9.1 ms
Desired period: 300ms or 2730 overflows

32. Liquid Crystal Display
USART on the ATmega128L
USART is dependent on the internal system clock and is highly sensitive. To reduce data error rates, an external system clock rated at MHz is chosen. Both devices (the LCD and the GPS receiver) are configured to transmit at 9600 bps with 8 data bits, 1 stop bit, no parity bit.
C1 = C2 = 15 nF
Liquid Crystal Display
Serial Device
USART0
Transmit pin
PE1 (#3)
Receive pin
PE0 (unused)
Baud rate
9600 bps
Frame Structure
8N1
GPS Receiver
Serial Device
USART1
Transmit pin
PD3 (#28)
Receive pin
PD2 (#27)
Baud rate
9600 bps
Frame Structure
8N1

33. LCD Commands Wrapper functions Native Commands Drawing
int lcd_clearScreen()
int lcd_setBacklight(int)
int lcd_setPixel(int,int)
int lcd_setX(int)
int lcd_setY(int)
int lcd_drawLine(int,int,int,int)
int lcd_drawCircle(int,int,int)
int lcd_drawBox(int,int,int,int)
int lcd_erase(int,int,int,int)
Command
Byte
Argument
Description
Clear Screen
0x00 —
Clears all written pixels.
Reverse Mode
0x12
Green-on-black pixel display.
Splash Screen
0x13
Toggles sparkfun logo at boot.
Set Backlight
0x02
0:100d
The number is decimal.
Set Baud Rate
0x07
“1:6”
Retained during power cycling.
Drawing
Command
Byte
Argument
Description
Set X Coordinate
0x18
0:127d
Moves cursor for text generator.
Set Y Coordinate
0x19
0:63d
Set/Reset Pixel
0x10
x, y, 0:1d
0: set (x,y) pixel, 1: reset (x,y) pixel
Draw Line
0x02
x1, y1, x2, y2, 0:1d
(x1,y1) to (x2,y2), 0: draw, 1: erase
Draw Circle
0x07
x, y, r, 0:1d
(x,y) center, r: radius, 0: draw, 1: erase
Draw Box
0x0F
Erase Block
0x05
x1, y1, x2, y2
Entire box is erased.

34. Parsing GPS Information
The only NMEA record used in the design is the Recommended Minimum Specific GNSS Data (RMC), which provides UTC time, date, latitude, longitude, speed over ground, and course over ground.
$GPRMC, ,A, ,N, ,E,2.69,79.65,100106,,,A*53
Name
Example
Units
Description
Message ID
$GPRMC
RMC protocol header
UTC Time
hhmmss.sss
Status A
A = data valid or V=data not valid
Latitude
ddmm.mmmm
N/S Indicator N
N=north or S=south
Longitude
dddmm.mmmm
E/W Indicator E
E=east or W=west
Speed over ground
2.69
Knots
True
Course over ground
79.65
Degrees
Date
100106
ddmmyy
Magnetic variation
Variation sense
E=east or W=west (not shown)
Mode
A=autonomous, D=DGPS, E=DR
Checksum
*53
<CR><LF>
End of message termination

35. Bike Buddy Temperature Sensor

36. Pull-up Supply Voltage
Parameter
Symbol
Condition
Min
Typ
Max
Units
Supply Voltage
VDD
Local Power
3.0 -
5.5 V
Pull-up Supply Voltage
VPU
Parasite Power
Sink Current IL
VI/O =0.4V
4.0 mA
Standby Current
IDDS
750
1000 nA
Active Current
IDD
VDD=5V 1
1.5
DQ Input Current
IDQ 5 µA

37. DS1625
Data is read from / written via a 2-wire serial interface (open drain I / O lines)
Temperature measurements require no external components
Measures Temperatures from -55°C to +125°C (-67°F to +257°F)
Converts temperature to digital word in 500 ms
Temperature is read as a 9-bit value (two byte transfer)
Parameter
Supply Voltage
Symbol
VDD
Min
4.5
Typ
5.0
Max
5.5
Units V

38. DS1625 Pin 1 SDA Pin 2 SCL Pin 3 Tout Pin 4 GND Pin 5 A2 Pin 6 A1
Data input/output pin for 2-wire serial communication port
Pin 2
SCL
Clock input/output pin for 2-wire serial communication port
Pin 3
Tout
Thermostat output. Active when temperature exceeds TH; will reset when temperature falls below TL
Pin 4
GND
Ground pin
Pin 5 A2
Address input pin
Pin 6 A1
Pin 7 A0
Pin 8
VDD
Supply voltage 5V input power pin

39. Digital Output (Binary)
DS1625
MSB
LSB 1
= -25°C
Temperature
Digital Output (Binary)
Digital output (Hex)
+125°C
7B00h
+25°C
1900h
+1/2°C
0080h
+0°C
007Fh
-1/2°C
FF80h
-25°C
E700h
-55°C
C900h
Temperature is represented in the DS1625 in terms of a 0.5°C LSB.
Not Using, Remains 0

40. Two Wire Interface (TWI)
A popular serial peripheral interface bus
TWI stands for Two Wire Interface and for most parts this bus is identical to I²C.
The name TWI was introduced by Atmel and other companies to avoid conflicts with trademark issues related to I²C.
-More flexible than SPI (Serial Peripheral Interface )
-Master and slave modes supported
-7-bit slave address
-Bidirectional, open-drain bus (device pulls down, resistors pull up)
-Two wires, SCL, (clock) and SDA (data)
Typical TWI bus configuration

41. Two Wire Interface A TWI transmission consists of
Start condition
An address packet consisting of
-Read/Write indication and
-Slave acknowledge, (SLA+RW)
One or more data packets
Stop condition
A Start condition initiates a transmission by a master.
Between Start and Stop conditions, the bus is busy and no other masters should try to initiate a transfer.
A Start condition is signaled by a falling edge of SDA while SCL is high.

42. Two Wire Interface Address packet -Address packet is 9 bits long
-MSB first
-Address “ ” is reserved for broadcast mode
-7 address bits (driven by master)
-1 read/write control bit (driven by master)
-1 acknowledge bit (driven by addressed slave)

43. Two Wire Interface Data packet -All data packets are 9 bits long
-MSB first
-One data byte plus an acknowledge
-During a transfer, Master generates SCL, Receiver acknowledges
-Acknowledge (ACK): Slave pulls down SDA in the 9th SCL cycle
-Not Acknowledge (NACK): Slave does not pull down SDA in 9th cycle

44. USB

45. WHY USB?
USB, became really popular nowadays to connect computer peripherals.
Not only for Data Source, but Power Source
A USB controller require to power one unit load, which is around 100mA.
such as fan, light, charging the batteries of mp3 players and cell phones.
USB has been become popular everywhere now , not only for the data source, but as power source

46. USB Types Parameter Requirement DC voltage, high-power port
4.75V to 5.25V
DC voltage, low-power port
Maximum quiescent current (low power, suspend mode)
500µA
Maximum quiescent current (high power, suspend mode)
2500µA
Maximum allowable Input capacitance (load side)
10µF
Minimum required output capacitance (host side)
120µF ±20%
Maximum allowable inrush charge Into load
50µC

47. USB Powering

48. USB Specs
Pin No.
Signal
Cable Color 1
+ VCC
Red 2
Data -
White 3
Data +
Green 4
GND
Black
Figure 3.22 shows demention and materials of female part of USB. It is most common type of USB, and it is rectangle shape. As it shown, it is small, it can be installed without limitation of space. USB port will be installed in the front side of the bike. This female part of USB will be covered with non-metalic materials to avoid any major or minor problems that could be occuer, and also protect it from outside circumstance.

49. Budget Product/Part Vendor/Service Actual Cost
ATmega128L dev board (STK300)
Kanda.com
$104.00
Serial graphic LCD 128x64
Sparkfun.com
$100.00
Bike generator 12V 6W
Bike World USA
$16.99
LS20031 GPS receiver
$60.00
2x 2-cell Li-Ion Battery packs
Powerizer.com
$40.00
Temperature sensor circuit
Digikey/Mouser
$20.00
USB port (female)
$4.00
Power supply circuit
$300.00
Battery charger circuit
$100
Battery switching circuit
Packaging/Misc. Hardware
Skycraft, …
$200
Extra cost
$300
Total
~$1300

50. Milestones Feb Mar Apr Feb. 26 Assemble prototypes of hardware systems
Build and test power supply
April 24
reBuild and retest power supply
Mar
Battery circuit built and tested
Feb
Mar
Apr
Feb
Successfully implement USART devices
Mar
Finish programming
Apr. 3-4
Assemble unit and attach to bicycle for final testing
Feb. 19
Complete part acquisition
Mar. 10
Complete basic software control flow

51. Bike Buddy
Group 15