Cathleen Shamieh

A pushbutton switch is a type of tactile (meaning touch) switch, which is an on/off switch that is activated when pressure is applied to it (usually by a finger).The figure shows one type of pushbutton switch. Each of the eight switches is a normally open, momentary single-pole, single-throw (SPST) pushbutton switch.

Diodes do a simple but important job: They allow current to flow in just one direction. A special kind of diode — a light-emitting diode, or LED — is often used for the purpose of, well, lighting up. You have to be careful to orient the LED the correct way, or current won't flow at all.Another kind of diode performs the important task of preventing current from flowing the wrong way in your circuit.

The figure shows the front and back of one type of mini-speaker. Speakers usually come with leads attached. The leads are twisted together to keep things neat and tidy. You attach the leads to components in your circuit so that electrical current passes from your circuit into the speaker. The speaker then converts the current into sound.

Pot is the shortened name for a potentiometer. A potentiometer (pronounced "poe-ten-shee-AH-meh-ter") is a variable resistor. The pot enables you to vary the blink rate of the LED without changing any components in your circuit.Pots come in various shapes, sizes, and values, but they all have the following things in common: They have three terminals (or connection points).

Discrete components are individual electronic devices, such as resistors, capacitors, LEDs, and transistors. You connect the components as you build circuits. An integrated circuit (IC) contains anywhere from a few dozen to many billions (yes — billions!) of circuit components packaged in a single device that can fit into the palm of your hand.

Look at the two 2N3906 PNP transistors shown here. Do they look like the 2N3904 NPN transistor? Yup. Does it matter if you get the 2N3904 and 2N3906 transistors mixed up? Yessirree, Bob! Two PNP transistorsIn this project, you use both a 2N3904 NPN transistor and a 2N3906 PNP transistor, so you really need to keep track of which is which.

A photoresistor, which is also called a light-dependent resistor (LDR) or photocell, consists of a piece of semiconductor material that exhibits an interesting characteristic: It acts like a resistor except that the value of resistance depends on how much light is shining on it.You can see an assortment of photoresistors in this figure, left, and a close-up of one photoresistor on the right.