Electronic components 1

In this chapter, you will learn about electronic systems and about components in electronic circuits. You will also learn about the following control devices: switches, diodes and transistors. Finally, you will make a simple transistor circuit. An electric circuit consists of an energy source and conductors. Conductors connect components such as input, output and process devices to create a path for the electrons to flow to and from the source of energy. Insulators are used to keep the components from short-circuiting.


Figure 1: A few examples of electronic components that we will deal with in this chapter


A switch controls the electric current by closing or opening the circuit. There are various types of switches that control the circuit in different ways. In this lesson, you will learn about manual switches that a user can turn on or off.

1. Think about different switches that you use daily and list them here:

Push button switch

Push button switches are often used for doorbell circuits, as in Figure 2. This simple doorbell circuit consists of cells in series, a push button and a buzzer, all connected by conducting wire. A person visiting the house presses the button for a short time and then releases it.


Figure 2: A simple doorbell circuit

2. Draw the circuit diagram of the doorbell circuit in the photograph. Use the correct circuit diagram symbols. Note that the cells are in series.

28198.pngSingle-pole, single-throw switch (SPST)


Figure 3: The symbol for an SPST switch


Figure 4: A typical light circuit with anenergy source, switch and lamp

Single-pole, double-throw switches (SPDT)ice 1 in one position and device 2 in the other position. There is no "off" position for this switch.

Figure 5: The symbol for an SPDT switch


Figure 6: A circuit with a battery, two lamps and an SPDT switch controlling two outputs


Figure 7: A circuit with two SPDT switches is often used to control a lamp with one switch at each end of a long passage. It is also used to control a lamp with one switch at the bottom of a staircase, and the other switch at the top of the staircase.


Figure 8

opposite direction. How can the direction in which the motor turns be changed? The way to do this is to change the direction of the current through the electric motor. Double-pole, double-throw switches can be used to reverse the direction of current through a circuit, so they are useful in applications such as automatic car gates. The circuit diagram below shows how a DPDT switch can change the direction of current through an electric motor.


Figure 9: A circuit where a DPDT switch controls the direction in which an electric motor turns

opposite direction when the current passes through it from terminal M2 to M1., to 4, to 2 and back to the negative of the battery.
  • from the positive terminal of the battery,
  • through the ON/OFF switch to 1,
  • through the top part of the DPDT switch from 1 to 5,
  • through the motor from M2 to M1,
  • to 6,
  • through the bottom part of the DPDT switch from 6 to 2, and
  • to the negative terminal of the battery.
  • Tech2_gr9_ch3_fig10.tif 

    Figure 10: A diode


    Figure 11: Circuit symbol of a diode. The current flow in a diode is in the direction of the arrow head.


    Figure 12: An LED. The longer of the two wires coming out of the LED should be connected to the positive terminal, and the shorter wire to the negative terminal.


    Figure 13: The circuit symbol for an LED.

    Tech2_Gr9_Ch3_Fig14.tif 33066.jpg collector, base and emitter.

    Figure 15: One type of transistor


    Figure 16: The circuit symbol for an npn transistor

    npn transistor acts as if there is a switch between the collector and the emitter. With a positive potential on the base of the transistor, the switch is closed. So it is an electrically controlled switch.

    There are other types of transistors, for example pnp transistors that work a bit differently from npn transistors. But you will only work with npn transistors in this term.


    Figure 17: A simple touch-switch circuit that will not work well

    npn transistor is a "control device," and the LED is the "output device".

    A transistor uses a small current circuit to switch on a larger current circuit. This is why transistors are also used in music equipment to "amplify" the sound.


    Figure 18: Circuit using a transistor as an electronic switch

    Tech2_gr9_ch3_fig19a.tif Tech2_gr9_ch3_fig19b.tif

    Figure 19: The construction of a touch-switch circuit with a transistor and an LED.