Joy-It RB-LCD-16x2 Manual

Joy-It Legetøj RB-LCD-16x2

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Side 1/15

Beginner’s Guide

to the

PI LCD

Part 4: Graphics

, W8BH

1) INTRODUCTION

In the rst three parts of this series, we learned how to display text and simple graphics on

the LCD board (available from mypishop.com). It’s time to kick it up a notch, and create a

suite of useful graphics functions. We’ll even create a large-digit clock. You may have

purchased either a 16x2 or a 20x4 display with your kit. In this write-up I’ll be using the

20x4 display. When it comes to graphics, bigger is better!

2) SIMPLE HORIZONTAL BAR GRAPHS

An important requirement for creating detailed graphics is that the display device is dot-

addressable. In other words, each display pixel can be individually addressed and

programmed, separate from its neighbors. Sadly, our HD44780 controller does not give us

a dot-addressable LCD display. We get only pre-determined characters, plus 8 characters

of our own design. How can we possibly do artwork on that?

Well, we can’t. Go ahead, prove me wrong. Detailed graphics with this LCD module are

devilishly hard to do. But that doesn’t mean we can’t create useful, simpler graphics. Bar

graphs, for example.

First, consider a single, horizontal

bar graph. Here is our 20x4

display, with a horizontal bar that is

12 characters wide. If we need to

display data that over a small

integer range, like 0-15, we can do it by repeating the solid block (0xFF) character for the

desired length. You might code it like this:

def HorizBar(row,startCol,length):

GotoXY(row,startCol) #go to starting position

for count in range(length):

SendByte(0xFF,True) #display bar of desired length

This simple code works, and is surprisingly useful. You aren’t limited to small ranges: just

scale the desired range to 0-15 by the appropriate conversion factor. But your graph will

always look a little coarse and chunky, since there are a limited number of possible data

values/lengths.

3 BETTER HORIZONTAL BAR GRAPHS)

The graph will look better if we improve the horizontal resolution. But how? We can get a

ve-fold improvement in resolution if we use the simple graphics from Part 3.

Consider the individual character. It contains 40 individual pixel “dots”,

arranged in an 8 row, 5 column grid. We can’t access each individual

pixel, but we can create custom symbols like this vertical bar. Display this

one to the right of the 12-character bar above, and you’ve just made a bar

of length 12.2!

Let’s make a set of vertical bar symbols, progressively increasing the

number of columns in the symbol

0.2 0.4 0.6 0.8 1.0

Now we can increment the length of our horizontal bar in fractions of a character, improving

the horizontal resolution of our graph. ime to code it. First, create the set of symbols, It’s t

like we did in part 3:

horizontalBars = [

[ 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10 ], #1 bar

[ 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18 ], #2 bars

[ 0x1C, 0x1C, 0x1C, 0x1C, 0x1C, 0x1C, 0x1C, 0x1C ], #3 bars

[ 0x1E, 0x1E, 0x1E, 0x1E, 0x1E, 0x1E, 0x1E, 0x1E ], #4 bars

[ 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F ] #5 bars

]

Now we need a routine to draw the horizontal bar for a given length. To simplify things, let’s

stay with integer lengths, and give each vertical bar a length of one (instead of 0.2). In this

system our original 12 character bar is 12*5 = 60 units long. Any length can be represented

Produkt Specifikationer

Mærke:	Joy-It
Kategori:	Legetøj
Model:	RB-LCD-16x2

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