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1. MX Lap Timer
An automatic stopwatch for
Motocross
Guilherme Pohl
Applied Electronics
Professor Walter Gontijo
December 9, 2014

2. Objective
● Develop an automatic stopwatch using an Infrared (IR) transmitter and
receiver to be used in Motocross
● Create an easy way to analyze your seasons
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3. Functionalities
● Calculate and display the current lap time
● Calculate the time difference between the current lap and the previous lap
● Display the best lap
● Software brighlight adjust
● Store the lap times in a .csv file
● Plot a lap time x lap graph in Excel
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4. Project Overview
This project can be divided into two modules:
● Transmitter module: Responsible for generating the pulse sequence
● Main Module: Responsible for calculate the lap time, the difference
between the previous lap, display the data on the LCD Display and store
the lap time into the SD Card
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5. Transmitter Design
5
Block Diagram of the Transmitter Module

6. Infrared (IR) Code
6
IR Code used in the MX Lap Timer

7. Transmitter Schematic
7
Transmitter Schematic

8. Transmitter PCB Layout
8
Transmitter PCB Layout

9. Transmissor Components
● 1x 6.8Ω Resistor
● 1x 1kΩ Resistor
● 1x 220Ω Resistor
● 1x 5mm Infrared (IR) Led
● 1x 5mm Blue Led
● 1x 100 nF Polyester Capacitor
● 1x 10 µF Electrolytic Capacitor
● 1x Transmitter NPN BD 233
● 1x Arduino Uno R3
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10. Main Module Design
10
Main Module Block Diagram

11. Main Module PCB Layout
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12. Main Module Schematic
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13. Main Module Components
● 1x 6.8Ω Resistor
● 1x 1kΩ Resistor
● 1x 220Ω Resistor
● 1x 1kΩ Linear Potentiometer
● 1x Buzzer 5V
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● 1x 5mm Blue Led
● 1x HD44780U LCD 20x4 Display
● 1x SD Card Module
● 1x VS1738 Infrared (IR) Receptor
● 1x NPN BC546 Transistor
● 1x Arduino Duemilanove

14. Infrared (IR) Receptor
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Block Diagram of the VS1738 Infrared(IR) Receptor

15. Infrared (IR) Receptor
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16. Infrared (IR) Receptor
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Infrared(IR) Receptor Input
Infrared(IR) Transmitter Output
Stop the transmission required by the
receptor to confirm the code’s receipt
Repeat

17. LCD 20x4 Display
The display has a parallel interface, this means the Arduino needs to control
many pins of the display at the same time in order to display the messages.
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Pins Utilized Connection
VSS GND
VDD +5V
VE Potentiometer Signal Pin
Register Select (RS) D9
Read/Write (RD/WR) GND
Enable (E) D8
D4,D5,D6,D7 D7, D6, D5, D4
Backlight Anode +5v
Backlight Cathode Collector of BC546

18. SD Card Module
This module communicate with the microcontroller using a serial peripheral
interface bus (SPI), that is a synchronous protocol used by the Arduino to
communicate with other peripherals and microcontrollers.
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SD Card’s Pin Arduino’s Pin
CS D10
SCK D13
MOSI D11
MISO D12

19. Software Fluxogram
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20. System Validation
The validation of the system was made analyzing the output of the IR
Transmissor and the input of IR Receptor signal pin utilizing an oscilloscope.
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21. System Validation
21
Zoom-in of one valid pulse

22. System Validation
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Zoom-in of the the Transmitter Output and the Receiver
Input

23. System Validation
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Delay of the Receiver Input signal

24. Computational Analysis
Analyzing the graph generated with the data acquired in one season is possible to
verify the rider's performance for each lap.
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25. 25
Thank you
Any Questions?