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Cheat Sheet

Electronics Projects For Dummies

From Electronics Projects For Dummies by Earl Boysen, Nancy C. Muir

Electronics projects often start with schematics that tell you what type of electronics to use where. Getting familiar with the symbols used in schematics takes you from “what the heck does this mean?” to completed electronics projects. Along the way, you’ll do some soldering, so you need to know how to stay safe while working with hot, molten metal. Some of the things you may be soldering include switches, so it pays to know about the various types and how they operate.

Symbols Used in Electronics Projects Schematics

If you get involved in electronics projects — building radios or metal detectors or motion detectors or whatever — it helps to know the symbols used in schematics. The symbols in the following list are those commonly used in North America and Japan; other countries use slight variations on these symbols:

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Safe Soldering Checklist

If you’re tackling an electronics project, you’re tackling soldering as well. Soldering poses a few different dangers: The soldering iron itself gets mighty hot; the solder (the material you heat with the iron) also gets hot; occasionally you even get an air pocket or impurity that can pop as you heat the solder and send bits of solder flying. Solder also produces strong fumes.

So, to stay as safe as possible, always follow these soldering safety guidelines:

  • Always wear safety glasses when soldering.

  • Never solder a live circuit (one that is energized).

  • Soldering irons come in models that use different wattages. Use the right size soldering iron for your projects; too much heat can ruin your board or components.

  • Solder in a well-ventilated space to prevent the mildly caustic and toxic fumes from building up and causing eye or throat irritation.

  • Always put your soldering iron back in its stand when not in use. Be sure that the stand is weighted enough or attached to your worktable so that it doesn’t topple over if you brush against the cord.

  • Never place a hot soldering iron on your work surface: You could start a fire.

  • Never, ever try to catch a hot soldering iron if you drop it. Let it fall, buy a new one if you have to — just don’t grab it!

  • Give any soldered surface a minute or two to cool down before you touch it.

  • Never leave flammable items (such as paper) near your soldering iron.

  • Be sure to unplug your soldering iron when you’re not using it.

Types of Switches Used in Electronics Projects

A switch seems simple enough: You flick it one way to go on and the other way to go off. With an electronic project however, understanding how different types of switches operate helps you decide which type to use where. The following lists describe the two states a switch can be in and what happens behind each type of switch.

The two states of a switch:

  • Open: A switch is in an open state when there is no electrical connection. When a switch is open, there is a very high resistance between a wire coming into the switch and the wire going out of the switch.

  • Closed: A switch is closed when there is an electrical connection. When a switch is closed, there is very low resistance between a wire coming into a switch and the wire coming out of the switch.

Switches are referred to by the method used to change their state open to closed:

  • Toggle switch: This switch gets its name from the fact that you flip a lever to turn it on and flip it back to turn it off.

  • Pushbutton on/off switch: Every time you push this button, the switch changes from on to off or vice versa.

  • Momentary pushbutton switch: Pushing this switch is what changes its state, but only for the moment! These are also classified by whether they are normally open or normally closed. For example, a momentary normally open switch is closed only while you hold the pushbutton down. When you release the button, it goes back to its normal open state.

  • Tactile switch: This is a type of momentary pushbutton switch. Tactile switches are rated by the amount of force needed to push the button and are often flat so that they can be easily inserted within a surface without protruding.

  • Slide switch: Logically, this switch operates when you slide a knob to change it from on to off or vice-versa.

  • Relays: These switches are operated by a voltage rather than by pushing a switch. This makes them very useful for turning on or off a component, such as a light or motor, through a remote control or by voltage generated by a sensor.

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