Application Note On Stopwatch 1

Stopwatch using microcontroller Prepared by Date

: TAN BENG HIN (HK2006-3620) : 25 MARCH 2009

Executive Summary This paper is to design and implement a stopwatch. A stopwatch is a handheld timepiece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated. The program of stopwatch was used the assembly language and implement to the hardware.

Introduction In this project, the stopwatch is controlled by three buttons. Pressing the first button start the timer running, the second button is stop the timer running and the third is reset the timer running. This stopwatch is available which due to their crystal oscillator because it is more accurate than mechanical timepieces. The result is shown on LCD when push then button.

Objective In this application notes, it gives people to learn and develop knowledge in designing the application by using the microcontroller. Besides that, it give way how to write an assembly language and combining with the hardware and also how the microprocessor can be embed with LCD display.

Issues The most important in this project is creating delay part. The microcontroller executed each instruction very fast.

Hardware System Description Voltage regulator is used to produce limited voltage supplied to PIC. This is important because PIC will burn out if the supply voltage more than 5.5 volt. Resistor of 1kΩ is used to bias the switch in order to have voltage drop as input signals to PIC. Switch is

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used to control the connectivity of input whether to produce 0 or 5 volt. This switch is turned ON when pressed and OFF when not pushed. PIC16F84A is used to burn into the assembled program, which will process the whole system of stopwatch. LCD of 8 bit input is used to show the process of stopwatch done by PIC such as start, running and stop. Crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. In this project, the frequency is used to keep track of time and provide a stable clock signal.

Software System Description There is two language can be use in order to program the PIC, that is either low level language that is assembly or high level language such as C programming and PIC Basic Pro. Both of the method has an advantage and disadvantages. In this project is using the low level language because the size of program cannot exceed 1K (PIC16F84A).

Step In this project, programming is the most important part to achieve a stopwatch. Before write a program, it is necessary to have a flow chart of the program stopwatch. The figure 1 shows the flow chart of the program stopwatch. After get the flowchart, the program code can be written now. The full program is shown in appendix A. The software that needed to write the assembly language is MPLAB Integrated Development environment (IDE), provided by Microchip. The advantage by using this method is the measurement of the time can be calculated. This PIC uses the external clock from the ceramic resonator 4MHz. each instruction line will be executed in 1µs. By using MPLAB IDE, we can observe the time executed by microcontroller by using stopwatch function in MPLAB. This can be obtain by choose Debugger

Stopwatch in MPLAAB

software. The figure 2 show the time elapsed and total instruction by microcontroller.

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Figure 1: The flowchart of the stopwatch program

Figure 2: Time executed by microcontroller

After build successful at MPLAB software, then now is the turn to build the circuit. Figure 3 show the example of full circuit. The software used to build and simulate the circuit is Proteus software. It is necessary to put the code that builds from the MPLAB inside the

PIC that we use. Double click the PIC then at the program file there inside the program, which is in HEX file. Then we can start to debugging and execute the stopwatch circuit.

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Figure 3: The example of full circuit of stopwatch

Result

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Figure 4: The LCD show the time is running when the start button is press

Figure 5: The LCD show that the time is stop running when stop button is press

Figure 6: The LCD show the start again when reset button is press

Conclusion After this project, you are able to learn and developed knowledge in designing by used a microcontroller. You also learn how to developed skills and knowledge in systematic

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design approach. Besides that we are know how the microprocessorcan be embed with LCD display.

Recommendation Stopwatch normally use at lab when doing experimental or sport usage. The concept of stopwatch can be apply to do digital clock, countdown or timer function, or calendar because the concept are almost same.

Reference 1. http://en.wikipedia.org/wik 2. http://www.pdfcoke.com 3. http://www.microchip.com 4. http://www.cytron.com.my

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