Transcript Meeting NCTE – 7th Feb 2008

Incorporating Computer
Control into Student
Project Work using a
PIC Microcontroller
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Building the PIC Control
Board
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CONTENTS
1. Printed Circuit Boards (PCBs)
2. Required PIC Board Components
3. Populating the PIC Control Board
4. Soldering Technique
5. Testing
6. Troubleshooting Hardware
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1. Printed Circuit Boards (PCBs)
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A printed circuit board also known as a PCB is a way of manufacturing
electronic circuits. A PCB is made from insulating plastic with copper
tracks connecting the holes where components are placed.
Courtesy of www.technologystudent.com
They are designed specially for each circuit and make construction very easy.
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PC Graphics Card
 PCBs are frequently used as a ‘Black Box’ technology in that they are
replaced completely in the event of a malfunction rather than attempting
to isolate the specific component that is causing the problem.
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2. Required PIC Board
Components
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Item No
PIC Board Code
Description
No. Required
per Board
SURFACE MOUNTED
1
R1,R4,R5,R7,R8
10K Resistor
5
2
R3,R6
4K7 Resistor
2
3
R15, R16
2K2 Resistor
2
4
R2
22K Resistor
1
5
R9,R10,R11,R12,R13,R14
330R Resistor
6
6
D1,D3,D10,D11
Diode 1N4001 50V
4
7
D2
Diode 1N4148 50V
1
8
IC2
18 pin low profile DILIC socket
1
9
IC1&IC4
7805 5V voltage regulator
2
10
C1&C4
Capacitor 100nF Polyester
2
11
C2&C3
Capacitor 220uF Electrolytic
2
12
Q1&Q2
BC337-40 npn transistor
2
13
TB1-TB6
2 way 16A PCB terminal block
6
14
CN1
2.1mm PCB DC Power Socket
1
FLYING LEADS
15
SW1
Miniature SPST momentary push switch
2
16
CN2
3.5mm stereo USB socket
1
17
Cable
10 way ribbon cable - rainbow
0.2 m
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Item No
PIC Board Code
Description
No. Required
per Board
OUTPUTS
18
D4&D7
5mm Red LED
2
19
D5&D8
5mm Green LED
2
20
D6&D9
5mm Yellow LED
2
21
N/A
LED Spacer mount
6
22
N/A
3v 8000 rpm motor
1
23
N/A
Miniature enclosed speaker
1
INPUTS
24
N/A
NORPS12 LDR
1
25
N/A
NTC Thermistor 20K
1
26
N/A
43mm lever solder microswitch
2
MICROCHIP
28
IC2
GENIE E18 IC
1
29
N/A
GENIE USB Plug & Play cable
1
MISC
30
N/A
Flexible propellor
1
31
N/A
Battery Clip PP3 End Entry 200mm
1
32
N/A
4 x AA Short Battery Holder
1
33
N/A
EI suppression capacitor
1
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Details of component suppliers for the PCB we are using are available
in the Excel file:
Student PIC Project Board Components.xls
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Details of the PCB we are using are available in the Excel file:
Student PIC Project Board Components.xls
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3. Populating the PIC Control
Board
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PCB Population Method
1. Start with the smaller components e.g. resistors and diodes.
2. Move on to larger components like the IC socket.
3. Finish surface mount with the tall components i.e. capacitors
and transistors.
4. Complete the population by connecting the components on
flying leads; power socket, USB and reset switch.
5. Do not connect the chip until the board has been tested for
power connection.
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Populate
Order
PIC Board Code
Description
Identification
1
R1,R4,R5,R7,R8
10K Resistor
Brown, Black,
Orange (Gold)
2
R3,R6
4K7 Resistor
Yellow, Violet, Red
(Gold)
3
R15, R16
2K2 Resistor
Red, Red, Red
(Gold)
4
R2
22K Resistor
Red, Red, Orange
(Gold)
5
R9,R10,R11,R12,R1
330R Resistor
3,R14
Orange, Orange,
Brown (Gold)
6
D1,D3,D10,D11
Diode 1N4001
Ensure correct
polarity
7
D2
Diode 1N4148
Ensure correct
polarity
Start now with the smaller components e.g. resistors and diodes.
Ensure correct alignment
of diodes
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Keep notch
to the LHS
Move on to larger components like the IC socket.
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Q1
Q2
TB1
TB2
C4
C1
TB4
TB5
TB3
TB6
IC1
IC4
C2
C3
Insert taller components; capacitors (C1-C4) , transistors (Q1&Q2), voltage
regulators (IC1&IC4) and terminal blocks (TB1 – TB4).
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CN1: 2.1mm PCB
DC Power Socket
PP3 Battery Clip
Insert power socket CN1 and connect the PP3 battery clip as
shown. This allows the board be powered from either the PSU
or 4 x 1.5V AA batteries.
NOTE: The red PP3 cable could be connected through
a SPST switch to create a master on/off control
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2.1mm Power Socket
If the project under construction requires the use of a 9V external PSU
then it is recommended to use an external power socket such as the
one shown above. These can be fitted into 3mm acrylic sheet.
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SW1 – Reset Switch
Complete the population by connecting the components on flying leads;
beginning with the reset switch SW1 as shown. It is possible to use 2
cables to connect the reset switch to the PCB by using 2 loops on the
board. However, the holes maybe too small to allow this.
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B
A
CN2: USB 3.5 mm Stereo Socket
For use in a project it will be necessary to mount the USB socket on a
flying lead as shown. The black and red cables may be connected in
the holes A and B if desired, as they are linked by copper trace.
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Q7
Q5
Q2
Q6
Q3
Q4
LED outputs may be connected
to outputs Q2 to Q7 using flying
leads so that they can be fitted
into a project where necessary.
Solderless LED holders are
available from some suppliers
fitted with 200mm leads that
retain the LED using a
patented clamping device.
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They are very useful for
ensuring that students do
not short out the LED legs.
It is cheaper to connect LEDs by
soldering ordinary cable.
Plastic LED leg spacers shown are
available from some suppliers.
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On the student project
board at the position for
outputs Q0 and Q1 there
are terminal blocks so
that outputs such as
bulbs and motors can be
attached. These outputs
require a larger current
than is available directly
from the PIC.
Q0
Q1
To overcome this a transistor is used with its base attached to
the PIC. The small current from the PIC is used to switch on the
transistor allowing a large current to enter the collector. This
makes it possible to use outputs like bulbs and motors.
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For the purposes of this
course we will use a small
speaker in output Q0 and
a motor in output Q1 as
shown above.
Q0
Q1
NOTE: Some DC motors
can cause the PIC to
malfunction due to
electromagnetic
interference or ‘noise’.
To counteract this, fit a 220nF capacitor directly across the motor
connections or use a solar type motor.
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We are using the following inputs:
D6: Micro-switch
D7: Push Switch PTM
D0/A0: NTC Thermistor 20K
D1/A1: NORPS12 LDR
NOTE: The 20K thermistor is being used instead
of a digital temperature sensor that is difficult to
source and expensive. Another terminal block
may also be added to allow easier connection.
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4. Soldering Technique
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Good soldering is necessary to ensure proper functioning of the PCB. If
possible, always use a temperature controlled soldering iron.
Click on the screen to activate a short video clip on soldering technique
courtesy of Youtube.
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Common soldering mistakes....
Too much solder
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Too little solder
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Unless joints with too little solder are corrected they can
eventually crack causing intermittent connection problems.
These can be very difficult to diagnose.
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‘Cold’ soldered joint – caused by incorrect technique
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Course participants are
encouraged to practice their
soldering technique if
necessary before
commencing.
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4. Testing
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Do not insert IC until
power supply has
been tested
Your completed PIC board should be tested to establish correct
power supply is present on the board and at the IC (5V) before
inserting the chip. NOTE: Never solder the board with the IC inserted.
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When you measure
across pins 5 and 14 in
the IC holder you should
read approx 5V.
If not then refer to the
slides on Troubleshooting
Hardware.
+5 V
PIN 18
PIN 1
0V
Otherwise, you are ready to insert the IC and begin using the GENIE
Design Studio software.
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4. Troubleshooting Hardware
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If you do not read approx 5V across pins 5 and 14 on your
IC then follow these steps:
1. Check your power source is working properly i.e. Check
your batteries or your PSU.
2. Carry out a visual check of components to ensure:
a. Components are inserted in the correct location e.g.
resistors and diodes.
b. Components are inserted with correct polarity i.e.
diodes, electrolytic capacitors, transistors.
c.
Components on flying leads are connected properly,
particularly the external power socket if used.
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If you still have not identified a problem then continue with
the following checks:
Check whether there is
supply voltage (6 or 9V
depending on batteries or
PSU) and whether the
voltage regulator has
reduced this to 5V for
use with the PIC as
shown.
6-9V
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0V
5V
If the problem still persists then it is probably due to a physical
malfunction such as a poorly soldered joint or a break or crack
in the copper trace. To identify this type of problem:
1. Carry out a visual check of all soldered joints and copper traces
using a suitable magnifying glass.
2. Check continuity between each component using the
multimeter.
3. Re-solder any joints that appear like those shown in slides 28 to
31.
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Student PIC Project Board Inputs & Outputs
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For further information on any
of these topics please refer to:
www.t4.ie
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