Download Prototyping Techniques and Soldering

Introduction to Electronics
Electronics Unit, Lecture 3
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Prototyping Techniques and
Soldering
Electronics Unit – Lecture 3
Schematic Diagrams
Assembly Methods
Soldering Tutorial
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Schematic Diagrams
Schematic diagrams represent an electronic
circuit in symbolic form.
A schematic need not depict the actual
physical arrangement of the components
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SkeeterSat Schematic
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Component Symbols
Wires and wire connections
Current practice:
Either A or B is acceptable
C is the preferred style
D is seldom used
E is interpreted as a non-connection
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Component Symbols
Power sources (V) and common connections (GND)
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Component Symbols
Resistors (R) and Capacitors (C)
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Component Symbols
Inductors (L) and Transformers (T)
simple
inductors
adjustable
tapped
The two parallel lines indicate
that the inductor is wound on a
core of iron, iron powder, or
ferrite material.
transformers
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adjustable
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Component Symbols
Diodes (D)
The arrow points in the allowed direction of
conventional (positive charges) current flow.
The bar represents the cathode, marked with a band on most parts.
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Component Symbols
Transistors (Q)
P-channel junction
field-effect transistor
bipolar NPN
junction transistor
bipolar PNP
junction transistor
N-channel junction
field-effect transistor
P-channel MOS
field-effect transistor
N-channel MOS
field-effect transistor
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Component Symbols
Integrated circuits (U)
Most complex integrated circuits are represented on schematic diagrams as a
rectangular block symbol, with pin numbers and, usually, pin functions indicated;
but many logic integrated circuits have special symbols that identify their function.
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Component Symbols
Switches (S) and Relays (K)
double pole single throw
DPST
single pole single throw
SPST
single pole double throw
SPDT
single pole double throw
relay
rotary switch
1 pole, 5 position
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double pole double throw
DPDT
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Component Symbols
Miscellaneous Components and Devices
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Drawing Schematic Diagrams
Use one of the many schematic capture programs available on the WWW
for free download, for example:
ExpressPCB
EagleLite
http://www.expresspcb.com/
http://www.cadsoftusa.com/freeware.htm
These usually include printed circuit board layout capability as well.
The SkeeterSat schematic shown earlier was prepared with ExpressPCB
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Building a prototype
Solderless breadboards
Perfboards or Protoboards
Manhattan Construction
Dead Bug Construction
Etched Circuit Boards
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Solderless Breadboards
The term breadboard originated in the
early days of radio, when many
experimenters actually built circuits on
the wooden boards used in their mother’s
kitchen for rolling out bread dough.
modern solderless breadboards
Best thing to come along since sliced bread!
A ham radio transmitter circa 1930
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Perfbord or Protoboard
Components are soldered to the board, with connections made
using a combination of short pieces of wire and the copper traces
already present on some versions of these boards.
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Manhattan and Dead Bug
Construction
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Etched Circuit Boards
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Soldering Tutorial
Soldering – fastening metal objects using molten
metal (solder) as the glue.
Three requirements
Low melting point metal (wire solder)
Heat source (soldering iron)
Flux (to prevent surfaces from oxidizing)
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Types of Solder
Tin-Lead solders
60% Tin, 40% Lead - solid at 361° F, liquid at 374° F
63% Tin, 37% Lead - eutectic point is 361° F
no “pasty” range so joint movement less a problem
Silver-bearing Solder
62% Tin, 36% Lead, 2 % Silver - solid at 354 ° F,
liquid at 372 F
often used for surface mount components whose
contacts contain trace amounts of silver
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Soldering Irons
Constant wattage
Iron is continuously “ON” and eventually reaches
equilibrium temperature
20 to 25 watt iron sufficient for circuit board assembly
Constant temperature
Tip incorporates a thermostatic element to maintain
desired tip temperature
650 – 750 ° F appropriate for circuit board assembly
Weller® 30 watt iron
But wait…..even better…
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Soldering Irons
Temperature Controlled Solder Station
Feedback control maintains tip at
desired temperature
Adjustable, often with analog or digital
temperature display
Many have grounded tip to help prevent
ESD damage
Weller® solder station
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Types of Flux
Rosin Flux
Type R – ordinary rosin – most common
Type RMA – mildly activated rosin
Type RA – activated rosin – use with care
Acid Flux – NEVER, EVER use this for electronics
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Flux-core solder
Most solder used for electronics assembly
is in wire form, with the flux incorporated
inside the solder.
Multi-core solder has several (usually five)
separate flux channels within the solder.
For circuit board assembly use wire solder
with a diameter of about 0.025 inch or less
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Soldering a Component
Use a lead bending jig, if available, to
form the component leads to the
correct spacing
If a bending jig is not on hand,
grasp the leads, not the body, of
the component with needle-nosed
pliers and bend gently.
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Soldering a Component
Insert the component’s leads through the
holes in the circuit board. The body
should lie flat against the board without
having to force it down.
Turn the board over and
gently bend the component
leads outward to hold the
component in place
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Soldering a Component
QT Movie Clip
Clean the iron tip by wiping on a damp sponge.
Tin the tip by applying solder, then wipe again.
Apply the iron in contact with both the
circuit board pad and the component lead.
Apply solder to the joint, not to the iron,
and allow the heated joint to melt the
solder
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Soldering a Component
Use a pair of flush-cutting wire cutters to cut off
the excess lead length as close to the board as
possible. Hold the lead so will not fly away when
cut, a possible occasion for eye injury.
!! WEAR SAFETY GLASSES !!
QT Movie Clip
Good soldering
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Inspect the soldered and
trimmed lead. It should be
uniform and shiny, with no
cracks, gaps, or graininess.
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Activities
E3a. Use the supplied assortment of components and
practice soldering them to the perfboard.
E3b. Locate each SkeeterSat component on the
schematic diagram, and then on the circuit board
layout. Be careful to note if the part has to be
oriented in a special way. You will actually
construct your SkeeterSat in the next session.
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