LSU 08/11/2004Electronics 31 Introduction to Electronics Electronics Unit, Lecture 3

LSU 08/11/2004 Electronics 3 1

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.

A schematic need not depict the actual physical arrangement of the components


SkeeterSat Schematic


Component SymbolsWires 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


Component SymbolsPower sources (V) and common connections (GND)


Component SymbolsResistors (R) and Capacitors (C)


Component SymbolsInductors (L) and Transformers (T)

simpleinductors

transformersThe two parallel lines indicate that the inductor is wound on a core of iron, iron powder, or ferrite material.

adjustableadjustable tapped


Component SymbolsDiodes (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.


Component SymbolsTransistors (Q)

bipolar NPNjunction transistor

bipolar PNPjunction transistor

N-channel junctionfield-effect transistor

P-channel junctionfield-effect transistor

N-channel MOSfield-effect transistor

P-channel MOSfield-effect transistor


Component SymbolsIntegrated 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.


Component SymbolsSwitches (S) and Relays (K)

single pole single throwSPST

single pole double throwSPDT

double pole single throwDPST

double pole double throwDPDT

rotary switch1 pole, 5 position

single pole double throwrelay


Component SymbolsMiscellaneous Components and Devices


Drawing Schematic Diagrams

Use one of the many schematic capture programs available on the WWW for free download, for example:

ExpressPCB http://www.expresspcb.com/

EagleLite 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

http://www.expresspcb.com/

http://www.cadsoftusa.com/freeware.htm


Building a prototype

Solderless breadboards

Perfboards or Protoboards

Manhattan Construction

Dead Bug Construction

Etched Circuit Boards


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


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.


Manhattan and Dead Bug Construction


Etched Circuit Boards


Soldering Tutorial

Soldering – fastening metal objects using molten metal (solder) as the glue.

Three requirementsLow melting point metal (wire solder) Heat source (soldering iron)Flux (to prevent surfaces from oxidizing)


Types of SolderTin-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


Soldering Irons

Constant wattageIron is continuously “ON” and eventually reaches equilibrium temperature 20 to 25 watt iron sufficient for circuit board assembly

Constant temperatureTip incorporates a thermostatic element to maintain desired tip temperature650 – 750 ° F appropriate for circuit board assembly

But wait…..even better… Weller® 30 watt iron


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


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


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


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.


Soldering a ComponentInsert 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


Soldering a ComponentClean 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

QT Movie Clip

QT Movie Clip


Soldering a ComponentUse 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 !!

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

Good soldering

Bad soldering

QT Movie Clip


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.

Documents

LSU 08/11/2004Electronics 31 Introduction to Electronics Electronics Unit, Lecture 3