Download Yr9_PIC_Chip

Y Pant School
The PIC Chip
Name/Door Plate
Year 9 Project
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Introduction
This is a major DESIGN and MAKE Project, but do not let that
worry you!
During years seven and eight you designed and made things using all
sorts of materials and processes. This project will draw on all of the
skills and knowledge learned during those projects and introduces
you to control to help you produce a useable product.
The Project
Situation
Control is used in electronic circuits to capture a person’s attention
and to follow a sequence of operations.
You have been asked to produce a name plate for a room of your
choice which will incorporate an electronic control circuit with LED’s
that you will programme to control the LED’s on your circuit.
Brief
Design & make a name/door plate for a room of your choice, which
will incorporate a PIC Control Circuit.
Brief 2
Design and make an electronic dice. The dice must show numbers 1-6
randomly by switching LEDs on and off.
Design & Specification Points
1) The design will use a picaxe08 microcontroller as its controller.
2) The design will include LEDs in a dice pattern.
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Organising your Project
We are going to use a combination of methods to make an attractive name plate.
To do this we will first ANALYSE the problem in class. An important factor is
your design work.
Before we do anything else it is necessary to outline two of the ESSENTIALS in
this project:
1. It must use a PIC Control Circuit.
2. It must house the circuit securely.
We are going to use a combination of materials to satisfy the requirements.
Everyone has used metal, wood, plastics, and electronics in projects. This
project is going to extend the skills that you have in a number of these areas.
The following pages describe electronic components and their uses. You will be
shown how to use them to produce a circuit that will help to illuminate your name
plate.
You will learn to produce the TECHNOLOGY currently used to control electronic
circuits, which influence what we ALL buy.
To help us produce the most attractive advertisement everyone will have
the opportunity to use the STIKA. This is a computer generated
manufacturing tool that copies your designs on to self-adhesive vinyl. It
will help you to produce a ‘real life’ advertising display.
The use of Electronics, Plastics, Timber, Stika-12 and Unimatic CAM will help
you to produce a high quality advertisement.
This project puts you in touch with the future, in how many other
things do you achieve the same thing, think about it?
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Designing with Electronics/Control
Using Electronics to solve design problems is not as difficult as you might
think. Most of you will remember the circuit you had to design for your
animated display; this circuit has a few more components but is not that
much more difficult to understand. It uses control.
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Electronic Dice
What is a microcontroller?
A microcontroller is often described as a ‘computer on a chip’. It can be
used as an ‘electronic brain’ to control a product, toy or machine.
The microcontroller is an integrated circuit (‘chip’) that contains memory
(to store the program), a processor (to process and carry out the
program) and input/output pins (to connect switches, sensors and output
devices like motors).
Microcontrollers are purchased ‘blank’ and then programmed with a
specific control program. This program is written on a computer and then
‘downloaded’ into the microcontroller chip. Once programmed the
microcontroller is built into a product to make the product more
intelligent and easier to use.
Example use of a microcontroller
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The picture above shows an electronic dice that can be made to generate
a random number. It can be used like a normal dice in games.
The dice works by switching Light Emitting Diodes (LEDs) on and off in
the pattern of dots found on a traditional dice. The microcontroller is
the ‘brain’ of the dice. Microcontrollers are powerful electronic
components that have a memory and can be programmed to switch things
on and off in any sequence. The microcontroller in the dice can switch
the LEDs on and off to show numbers between one and six.
As the ‘diagonal’ pairs on LEDs in the dice always light at the same time,
they can be switched on and off by the same microcontroller output.
Therefore 4 outputs (3 pairs and central ‘dot’) are required.
Block Diagrams
The electronic system for an electronic dice can be drawn as a ‘bock
diagram’.
Input
Push
Switch
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Process
Microcontroller
Output
LEDs
The push switch is an electronic device that can detect movement and is
known as an ‘input’. The microcontroller then ‘decides’ how to behave and
may then switch the output LEDs on in different patterns.
What is the PICAXE System?
The microcontrollers used in devices such as electronic games can be
difficult to program, as they generally use a complicated programming
language called ‘assembler code’, which can be quite difficult to learn.
The PICAXE system makes the microcontrollers much easier to program.
The control sequence can be drawn (and simulated) on the computer as a
flowchart, or written in a simpler programming language called BASIC.
This makes it much easier to use the microcontroller as the complicated
‘assembler code’ does not need to be learnt.
A simple BASIC program and flowchart are shown here. In this case both
programs do the same thing – flash a light (connected to output 0) on and
off every second.
Main:
high 0
wait 1
low 0
wait 1
goto main
start
high
wait 1
low 0
7
wait 1
Personalising your Electronic Dice
There are several ways to personalise your electronic dice name plate.
Here are some things to think about:

Your LEDs and switch will need to be fixed to the circuit using
wires. As the name plate will house the circuit.

What colour LEDs are you going to use? The most common LEDs
are red, but many other sizes and colours are available (e.g. blue)

How will you activate the dice? We are going to use a push switch
but you could have a light sensor (LDR) that can detect changes in
light level when you put your hand over it.
Electronic Components
The main electronic components you may need for you electronic dice are
shown here.
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
PICAXE-08 microcontroller

Light Emitting Diode (LED)

Push Switch

3 x AA Battery Box

Picaxe Download socket
Electronic
Components Microcontrollers
 Resistor
What is a microcontroller?
A microcontroller is often described as a ‘computer on a chip’. It can be
used as an ‘electronic brain’ to control a product, toy or machine.
The microcontroller is an integrated circuit (‘chip’) that contains memory
(to store the program), a processor (to process and carry out the
program) and input/output pins (to connect switches, sensors and output
devices like motors).
Microcontrollers are purchased ‘blank’ and then programmed with a
specific control program. This program is written on a computer and then
‘downloaded’ into the microcontroller chip. Once programmed the
microcontroller is built into a product to make the product more
intelligent and easier to use.
Where are microcontrollers used?
Applications that use microcontrollers include household appliances, alarm
systems, medical equipment, vehicle subsystems, and electronic
instrumentation. Some modern cars contain over thirty microcontrollers
– used in a range of subsystems from engine management to remote
locking!
As an example, a microwave oven may use a single microcontroller to
process information from the keypad, display user information on the
seven segment display, and control the output devices (turntable motor,
light, bell, and magnetron)
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How are microcontrollers used?
Microcontrollers are used as the ‘brain’ in electronic circuits. These
electronic circuits are often drawn visually as a ‘block diagram’.
Input
Process
Output
The program for the microcontroller is developed (and tested) on the
Door Switch
Microcontroller
computer and then downloaded into the microcontroller. Once the Bell
program is in the microcontroller it starts to ‘run’ and carries out the
instructions.
How is the program transferred to the microcontroller?
The PICAXE-08 microcontroller is programmes by connecting a cable
from the serial port at the back of the computer to a socket on the
printed circuit board (PCB) beside the microcontroller. This socket
(which looks like a head phone socket as found on an MP3 Player) connects
to two legs of the microcontroller and to 0V from the battery. This
allows the computer and the microcontroller to ‘talk’ to allow a new
program to be downloaded into the microcontrollers memory.
The socket and interfacing circuit is included on every PCB designed to be
used with the PICAXE-08 microcontroller. This enables the PICAXE
microcontroller to be re-programmed without removing the chip from the
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PCB – simply connect the cable whenever you want to download a new
program!
BATTERIES
What is a battery?
A battery is a self-contained source of electronic energy. It is a portable
power supply. Batteries that contain chemicals that store energy. When
connected into a circuit this chemical energy is converted to electrical
energy that can then power the circuit.
Which battery size should I use?
Microcontrollers generally require 3 to 6V batteries to work, and so it is
better to use a battery pack made up of two, three or four AAA or AA
size cells. Never use a 9V PP3 battery as the 9V supply will damage the
microcontroller.
Which battery type should I use?
Different batteries are made of different chemicals. Zinc-carbon are
the cheapest, and are quite suitable for many microcontroller circuits.
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Alkaline batteries are more expensive, but will last much longer when
driving devices like motors that require larger currents.
Lithium
batteries are much more expensive but have a long life, and so are
commonly used in computer circuits to provide a clock back up.
Rechargeable can be recharged when they ‘run-down’. They are generally
made up of nickel and cadmium (Ni-cad) or nickel metal hydroxide (NiMH)
chemicals.
SAFETY!
The microcontroller chip will be damaged if the battery is connected
incorrectly.
Using Battery Snaps
Battery packs are often connected to electronic printed circuit boards by
battery snaps or wires. Always ensure you get the red and black wires
the correct way around. It is also useful to thread the wires through
holes on the board before soldering it in place – this provides a much
stronger joint that is less likely to snap off.
Never accidentally connect a 9V PP3 battery to the battery snap – this
will damage the microcontroller, which only works between 3 and 6V.
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Resistors
Resistors are very important in electronics because we often have to limit
the amount of current flowing in a circuit or parts of it. The most
common resistors consist of a thin film of carbon over a ceramic tube,
each end of which has a wire connecting leg. The resistance simply
depends on the type of carbon used.
Carbon Film is in the
middle of the Resistor.
Resistors are colour coded with four bands that can be read to give their
values in ohms. The higher the number in Ohms, the greater the
resistance.
To read a resistor’s value, look at its first colour band (opposite end to
the metallic band) and find this colour on the chart. Now look across the
chart to Column 1 and note the number. Do this for the other two colour
bands, going across the chart to Column 2 and then to Column 3.
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If, for example, the resistor’s first colour band is yellow, we note ‘4’ in
Column 1 on the chart. If the second band is violet, we go across to
Column 2 and note ‘7’. If the third is red, we see two noughts in Column 3,
giving a figure of 4,700. This is the value in ohms of the resistor.
The Resistor
Gold + or – 5%
Silver = or – 5%
Colour
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Band 1
0
1
2
3
4
5
6
7
8
9
Band 2
0
1
2
3
4
5
6
7
8
9
Band 3
Nothing
0
00
000
0000
00000
000000
Work out the resistance values of these resistors
Colour
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Band 1
Band 2
Band 3
Total
Blue
Grey
Brown
Red
Red
Red
Brown
Black
Red
The LED
Most of the circuits use a light emitting diode (LED) rather than a bulb.
LED’s give out less light, but they use less current and cost less. LED’s
also come in three colours: red, green and amber.
Unlike a bulb, an LED does not have a filament. It is too hard to explain
here how it works, but it is easy to use if you follow two simple rules:
Examples of different
LED’s.
Symbol for and LED
LED Rule 1
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An LED must be used with a resistor in the circuit loop. This restricts
current flow and prevents the LED taking more current than is good for
it. If an LED takes too much current it will break.
LED’s are small in size,
they are 39mm.
LED Rule 2
An LED must be connected in a circuit with its (-) leg facing towards the
(-) terminal of the battery. If you look at they bottom of an LED, there
is a small flat edge on the plastic, and the (-) leg is nearest to this.
An LED is a diode. This lets current pass only when it is connected in a
circuit the right way around. If it is connected backwards, nothing
happens and no light.
Diagram Shows LED
Symbol, Flat side of
LED, Shorter and
Longer legs.
Connecting the LED to a microcontroller.
Because the LED only requires a small amount of current to operate, it
can be directly connected between the microcontroller output pin and 0V
(with the series protection resistor). Two LEDs can be driven from the
same pin if you use the resistor for each LED.
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After connecting the LED it can be
tested by a simple program like this:
main:
high 0
wait 1
low 0
wait 1
goto main
This program would switch the LED
on and off every second.
If your LED does not work check:
1.
2.
3.
4.
the LED is connected the correct way around.
the correct resistor is used.
the correct output pin number is being used in the program.
all the solder joints are good.
This program flashes the LED connected to output pin 0 on and off 15
times using a BASIC programming technique called a for…next loop (this
technique cannot be used with flowcharts). The number of times the
code has been repeated is stored in the memory of the PICAXE chip using
a ‘variable’ called b1 (the PICAXE contains 14 variables labelled b0 to
b13). A variable is a ‘number storage position’ inside the microcontroller
than the microcontroller can use to store numbers as the program is
carried out.
main: for b1 = 1 to 15
high 0
pause 500
low 0
pause 500
next b1
end
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‘ start a for…next loop
‘ switch pin 0 high
‘ wait for 0.5 second
‘ switch pin 0 low
‘ wait for 0.5 second
‘ end of for…next loop
‘ end program
Switching more than one LED at once
Sometimes it is useful to switch more than one LED on or off at the same
time. This saves time when lots of high and low commands would have to
be used together.
Pin
4
2
1
0
Value
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4
2
1
The command that does this is called let pins =
After the equals sign a number is used. Each output pin is given a value,
and the number used in the program is the sum of these values.
Digital Sensors (Switches)
What are switches?
A digital sensor is a simple ‘switch’ type sensor that can only be ‘on’ or
‘off’.
Switches are electronic components that detect movement. There are a
large number of different types of switches e.g.


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Push switches that detect a momentary ‘push’
Micro-switches with long levers that detect small movements


Tilt-switches that detect jolting
Reed-switches that detect a magnet being moved
What are switches used for?
Push switches are commonly used on device like keypads. Micro-switches
are used in burglar alarms to detect if the cover is removed from the
alarm box. Reed switches are used to detect doors and windows being
opened and tilt switches are often used to detect movement in devices
such as toys, hair-dryers and tool-box alarms.
Switch Symbols
The symbol for a slide switch and a push switch are shown here.
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Printed Circuit Boards
Modern electronic circuits use only a few wires to connect the main parts
together. The components are held together on a printed circuit board
called a PCB.
Printed circuit board is a thin fibreglass board about 1.5mm thick. On
one side of the board is a layer of copper, only about 0.25mm thick. To
use the board we must first draw our circuit onto the copper using a
special etch resist pen. Take great care at this stage because once the
board is placed into the etch tank mistakes cannot be altered.
PCB Layout
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A PCB Board
with
Components.
Etching
When you are happy with your circuit, you are ready to place it into the
acid (Ferric Chloride). This will eat or etch away all the copper not
protected by the special etch resist pen. Take care with this, as it is
poisonous and corrosive, don’t get it on your clothes or hands!!!
Once all the unwanted copper has been removed you can use the tongs to
remove your circuit from the acid and then was it under the cold-water
tap. The etch resist pen must now be removed to leave only the copper
tracks ready for us to start drilling. Use wire wool to remove the etch
pen.
An Etching Tank
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Note the protective gloves that must be worn when using this machine. You can see
the PCB in the acid, which is removing the copper, which is not needed.
After a circuit
board has been
placed into an
Etching Tank the
circuit tracks are
left in pen. Once
rubbed with wire
wool copper is
exposed.
Drilling
You will now need to drill holes in the circuit board for attaching the
components. The pins or legs of the components must pass through the
board, so they can be soldered to the copper side. To make these small
holes you will need a very small drill bit, which is easily broken if not
handled with care. Take your time and don’t forget to wear safety
glasses!!
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e-Printed PCB
Holes being drilled into a PCB
board.
The drill bit is very
small!!! So, be
careful.
Soldering
Take care when using soldering irons, avoid burning the leads and always
replace them in the soldering iron stand when you are not actually using
them. Do not leave them lying on a workbench.
The component pins and the board should be cleaned with a piece of fine
wire wool before soldering. The soldering iron bit is heated and then
‘tinned’ by putting a small amount of multicore solder on it. The solder is
hollow and has flux inside. Flux helps to keep the joint clean while it is
being heated. It is very important that the work is heated properly, in
order to get a good joint, which makes good electrical contact.
Hold the tip of the iron on the copper next to the component. Place the
solder onto the copper next to the iron. When the work is hot enough
the solder will melt and flow. Remove the solder and run the tip of the
iron around the pin of the component to make sure it is properly joined to
the copper.
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Example of Soldering Iron
Stand, Soldering Iron and Power
Source. The power source is
used to control current and
heat.
Always ensure
the solder joint is
neat and not
crossing the
tracks.
Always solder electronic
components correctly to a
PCB, if you do not the circuit
will not function and the
components could break.
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Remember to follow Health &
Safety Rules!!!
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