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Introduction to Electronics. Electronics Unit, Lecture 3. Prototyping Techniques and Soldering Electronics Unit – Lecture 3. Schematic Diagrams Assembly Methods Soldering Tutorial. Schematic Diagrams. Schematic diagrams represent an electronic circuit in symbolic form.

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Introduction to Electronics

Electronics Unit, Lecture 3

Electronics 3


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Prototyping Techniques and SolderingElectronics Unit – Lecture 3

Schematic Diagrams

Assembly Methods

Soldering Tutorial

Electronics 3


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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

Electronics 3


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SkeeterSat Schematic

Electronics 3


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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

simple

inductors

Inductors (L) and Transformers (T)

adjustable

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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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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P-channel junction

field-effect transistor

bipolar PNP

junction transistor

bipolar NPN

junction transistor

N-channel junction

field-effect transistor

P-channel MOS

field-effect transistor

Component Symbols

Transistors (Q)

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

double pole single throw

DPST

single pole single throw

SPST

Switches (S) and Relays (K)

single pole double throw

SPDT

double pole double throw

DPDT

single pole double throw

relay

rotary switch

1 pole, 5 position

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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:

ExpressPCBhttp://www.expresspcb.com/

EagleLitehttp://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

But wait…..even better…

Weller® 30 watt iron

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Soldering Irons

Feedback control maintains tip at desired temperature

Adjustable, often with analog or digital temperature display

Many have grounded tip to help prevent ESD damage

Temperature Controlled Solder Station

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

Clean the iron tip by wiping on a damp sponge. Tin the tip by applying solder, then wipe again.

QT Movie Clip

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

QT Movie Clip

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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

Inspect the soldered and trimmed lead. It should be uniform and shiny, with no cracks, gaps, or graininess.

Bad soldering

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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.

Electronics 3


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