labexcercise_2

8/13/2019 LabExcercise_2

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Miguel Alejandro Alvarado Vzquez A01222725 Microcontrollers

Rodrigo Navarro Romero A01221761 Prof.Diego Villa

Diego Alejandro Cerda Contreras A01222445 14/09/2011

MicrocontrollersLab Exercise 2

Keypad and LCD display

Introduction

In this second exercise, the challenge was to build from scratch a driver for a keypad andto use a LCD to display text on it. The objective was to develop a prototype that simulates the

behavior of a microwave using the two modules mentioned before.

The hardware was very easy; we just have some small problems that we fixed quickly. Here is the

hardware diagram that we used to implement the hardware:

Hardware Diagram

For the second lab exercise we had to design the operation of a microwave oven, we also

needed to implement a driver for a matrix keypad. We made two functions, one function to

control the keypad and to return the value we got from it, and the other to just send one time the

desired number just once. For the microwave oven we made just one single function to control the

uC

PIC18F4620

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4VCC

VCC

VCC VCC

VCC

5V

C1

15pF

C215F

C5

100nF

C6

100nF

10k

K1

1 2 3 A

4 5 6 B

7 8 9 C

* 0 # D

470 X4

X410k

LCD

VSS1

VDD2

ADJ3

RD4

WR5

A06

D07

D18

D29

D310

D411

D512

D613

D714

CS15

RST16

DOFF17

NC18

BL-A19

BL-K20

2.2k

VCC5V

15

VCC5V

10k

RST

CS

RD

WR

A0

RD

WR

10k

VCC

RST

CS

A0

Dip

LED

Dip

J1

LED 100

LED1

200

LED2

100

LED3


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the display of the numbers in the lcd screen and also because we could check if the time was a

valid number or not. To set a time we check if the input received from the button is a number, if it

is was, we shifted the values in the array to the left and then setting the input value in the less

significant index of the value. If the input is a letter we simply setup a predefined time. If the input

was the star then we assumed the user wanted to cancel the input so we just set the time to

zeros. Finally if the input was the pound sign we know that the user wants to start, so first we

checked if the time is bigger than 0000, if not we set the time at 30s. After that we set the variable

telling the microwave oven is on to 1.

The first thing we do if the microwave oven is on is checking if the time is a valid input,

that means a time lower than 1 hour and with less than 60 seconds, if time is invalid we correct it.

Then we check if we received as an input from the keypad, if we received one we check if the

input was a star, if it was we simply set the count to zero and put the microwave off. If the input

was the pound sign we ad 30 seconds to the count, if the input was any other button we simply

ignore it. If the oven door is open at any time, it enters a cycle that does nothing but keeping the

heart beat LED blinking. The only way to leave that cycle is to close the door and pressing thepound button, so that the count would start from it left it off, or by pressing the star button

making the countdown go to zero.

Every second we decrease a number in the countdown, decreasing a number is a little

complicated because we have to make special conditions because the second bit goes from 0 to 6

and so does the zero bit.

No matter if the microwave oven is working or not, we have to display the time on screen,

so after both ifs we print Time Left: followed by the number in the time array in index 0, in index

1, :, in index 2 and in index 3.

When the time is finished, we put the microwave oven as not working and call the buzzer

method.

The buzzer methods counts to 30 seconds, it makes a buzzer ring every time that number

is overflowed, if the door is opened at any time, it leaves the cycle and returns to the microwave

oven functionality function.

While implementing the microwave oven we found many difficulties. The most important

ones were difficulties from getting the inputs from the keypad, mainly because sometimes we

needed a value to be recorded as input only one time, but in other functions we needed a

continuous input. To solve this we implemented another method in the keypad driver so that it

could return an input as a pulse or as a continuous function.

The more difficult issue we had was to implement the heartbeat LED, to do this we

standardized all the delays in the method. We refreshed the screen every .5 seconds, so we had to

make the rest of the delays in the function to add up to .5 seconds, so every time the screen is

refreshed we could toggle the heart beat LED.


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Also we werent able to control the time accurately due to the overhead our functions

had. We tried with the oscilloscope and by comparing our countdown with a real chronometer to

check if we had an accurate approximation to a 1 second count in the microwave oven

implementation.

Conclusions:

Rodrigo Navarro Romero: With this lab exercise I learned how to implement many debug

techniques such as printing 0xff at an output port if any condition was met, in order to check if the

program operated correctly, other debug technique I learned to implement was to make bigger

delays, so that you can check all the functionality of the program step by step. I also founded out

that no matter how deep you check the software in order to find issues, you can still have really

silly mistakes in hardware, which are very simple to solve, but very hard to find.

Diego Alejandro Cerda Contreras: Every time I get more and more excited about microcontroller

applications, now I can see that there is no limit about the implementation you can reach using

this kind of technology. I realize that using somebodys code is a quick fix for our problems, for

instance, in this case the LCD driver, but I can say that our Keyboard implementation was difficult

to develop, we had a lot of issues trying to get a proper functionalities, I discover that the using of

simple code tricks to debug is very helpful, I also found that we have very other benefits when

programing the keyboard driver, also more control of it, and of course more customization.

Miguel Alejandro Alvarado Vzquez:Again for me this was a very interesting Lab Exercise because

of the introduction of a keypad and a LCD. At the beginning we focused on the development of the

keypad driver and it was good until we start getting problems. One of the issues that we had with

the keypad was very annoying because we couldnt fix it, so we decide to change the way the

keypad driver was working. With this problem I found that sometimes the best solutions is the

easiest way. Also at the beginning we have some basic hardware problems that were fixed with no

effort.

For the part of the LCD I hadnt written text on it (only images). So I needed to learn on how to

print a string on it but at the end it was no so difficult. In general working with the LCD is not

difficult the problems that we encounter were hardware problems and that the LCD sometimes

doesnt respond very well.

In this exercise I learned that you must pay attention on what are you doing, because if the logic is

wrong, the program will not function properly and you will think that its a hardware issue, of

course this happened to us and because of that, we lost a lot of time until we finally found that it

was a software problem.


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Keypad_Value

Buttons == Las_Value

If(No_Repetition)

Yes

No_Repetition=1

No

No_Retition=0

Return_Value =Buttons

Yes

Return_Value = 0xffNo

Last_Value=ButtonsRetunr

Return_Value

Diagram for Keypad_Valuefuction.


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LCD_Microwave

Microwave OnIs time an invalid

number

Keypad_Input is

a number?NoYes

Keypad_Input is a

predefined time?

Keypad_Input is

the cancel button

Keypad_input is

the start button

NO

NO

NO

Time= Time


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Buzzer

K=0

L=0

Is K==1?

Is K==29

NO

Is the door

opened

NO

Delay ms (200)

L++

Is L==4?

Heart beat LED

L=0

K++

YES

Ring the buzzer.

K=0

NO

K=32

L=8

Is k< 30 Exit functionNOYES

YES

YES

YES

NO

Diagram of the Buzzer function.


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.5Hz Frequency of the Heart Beat LED.

.5Hz Frequency of the Heart Beat LED


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Hardware Implementation.

Final Prototype.

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