Basic Electricity & Electronics

1. Basic Electricity & Electronics Let’s go on a Learning Journey

2. Conductors and Insulators Metals are good conductors because current flows through them easily. Wood and most plastics do not allow current to flow and are electrical insulators. Some materials, such as silicon and germanium, are called semi-conductors because current flows through them, but not as freely as through metals.

3. SWITCHES • A switch with two connections is called a single-pole, single-throw (SPST) switch. • A switch with three connections is called a single-pole, double-throw (SPDT) switch. SPDT

4. SWITCHES • A double-pole, double-throw (DPDT) switch has six contacts. DPDT can operate two independent circuits at the same time. DPDT

5. R1 R2 RESISTORS in series • When resistors are connected in series, the combined resistance is higher than the individual resistances • Worked out by adding each individual value to the next. R = R1 + R2

6. R = R1 + R2 111 R1 R2 RESISTORS in parallel • When resistors care connected in parallel, the combined resistance is lower than the individual resistances worked out by adding the reciprocal of each individual value to the next.

7. Use of RESISTORS • Resistors reduce the amount of current flowing in a circuit and are used for protecting components from being damaged by too much current. • They are made in a range of values, with higher values providing a greater resistance. • Resistors can be connected either way round in a circuit.

9. RESISTORS

10. BIPOLAR TRANSISTOR • A transistor is an automatic switch. • Instead of pushing a button or sliding a lever to turn it on or off, it has a contact, called the base, which is used to activate it.

11. Types of SWITCHES Rocker switch Rotary switch Slide switch Push switch Tilt switch Microswitch Membrane panel switch Reed switch Key switch

12. OUTPUT COMPONENTS • The filament bulb lights up when current passes through. • The current causes the filament to become so hot that it glows.

13. OUTPUT COMPONENTS • Buzzers make a noise when connected to a battery and are often used as warning devices. • The wires are sometimes coloured coded: red to connect to the positive terminal and black to connect to the negative terminal.

14. OUTPUT COMPONENTS • Motors are used for turning wheels, pulleys, gears or cams. • D.C. brush motors having contacts for the battery connection are the most common type. • The direction of the spindle rotation can be reversed by swapping the connections at the contacts. • The larger the motor, the more current it requires.

15. Stepper Motor • A stepper motor has a permanent magnet rotor that turns inside fixed coils of wire. • The coils are switched on and off in a special sequence to turn the rotor. • They are precise because the rotors can be made to turn through an exact number of steps.

16. Solenoid • A solenoid also produces a linear movement. • It consists of a coil of wire with a plunger in the centre. When the current flows through the coil, it creates a magnetic field, causing the plunger to move through the coil.

17. NC NO Relay • A relay is a switch which is operated by a small solenoid. • The relay allows a low voltage circuit called the primary circuit to control a high voltage circuit called the secondary circuit. • It also allows high current devices to be switched on and off by a circuit which uses a much smaller current.

18. flat side indicates cathode anode anode (+) cathode (-) cathode OUTPUT COMPONENTS • A light-emitting diode (LED) glows when a current flows through it. • LEDs are cheap and come in a variety of colours. • The leg next to the flat side of the LED is to be connected to the negative terminal of the battery.

19. anode (+) cathode (-) OUTPUT COMPONENTS • Diodes allow an electric current to flow through in one direction only. • They are used in circuits for controlling the flow of the current. • A standard semiconductor diode does not light up when current flows through it. anode cathode

20. Components and Uses

21. Components and Uses

22. Components and Uses

23. Components and Uses

24. Components and Uses

25. Components and Uses

26. Draw a simple electrical (light) circuit to show: (a) its components and (b) its symbols at its switch-off position Include energy source Battery, light bulb and a switch (b) (a)

27. How are components temporary connected in a circuit Components can be temporarily connected using terminal blocks. The plastics covering of the wires must be removed from the ends before they are inserted in the terminal blocks.

28. Bulbs in a Parallel Circuit Bulbs in a Series Circuit

29. Components connected in series and parallel circuit A C B

30. What is a transistor? • The transistor is an automatic switch that can be operated by a sensor and has three legs called the base, collector and emitter. • Sensor is connected to the base; positive terminal of the battery towards the collector; negative terminal towards the emitter.

31. Draw the transistors and its symbol Positive negative

32. Explain how the input sensor and transistor works? • As the sensor detects environmental changes, it causes a voltage change at the base of the transistor. • When the voltage rises above 0.6 V, the transistor switches on, allowing current to flow from the collector to the emitter.

33. INPUT PROCESS OUTPUT thermistor fan transistor What is an open loop system? • In an automatic cooling system, when a thermistor (input) senses a rise in the temperature, a propellor blade (output) connected to a motor is turned on by the transistor. When the temperature falls, the transistor switches off. • This is an open loop control system because the fan does not actually cool the air.

34. INPUT PROCESS OUTPUT moisture transistor water pump FEEDBACK What is a closed loop control system? • In an automatic water pump, when a moisture sensor (input) detects water, a water pump (output) operates when the transistor switches the circuit on. When the water level is clear of the sensor, the transistor switches off.

35. to sensor to output component to battery transistor variable resistor copper tape Explain how you can construct a simple transistor circuit • The transistor circuit is easily constructed using self-adhesive copper tape and a soldering iron. • The tape may be stuck to a small sheet of wood, plastics or card and the components are soldered directly to the tape. • The addition of a variable resistor allows the sensitivity of the circuit to be adjusted

36. BIPOLAR TRANSISTOR • A very small current at the base will switch on the transistor, allowing a much larger current to flow between the collector and emitter.

37. BIPOLAR TRANSISTOR • The base of a transistor is usually connected to a sensor, such as a light or temperature sensor, which determines the amount of current flowing into the base. • When the sensor allows enough current to flow, the transistor switches on. • A resistor is normally connected to the base of a transistor to prevent it from being damaged by too much current.

38. BIPOLAR TRANSISTOR • In a P-N-P transistor, current is allowed to flow from the emitter to the base and from the emitter to the collector.

39. SENSORS • In dry conditions, there is a very high resistance between the contacts of the sensor. No current is able to flow into the base and the transistor is switched off. In dry conditions, no current flows into the base of the transistor so the LED is off.

40. SENSORS • In damp conditions, the resistance between the contacts is much lower. A small current flows into the base and the transistor switches on. In damp conditions, a small current flows into the base of the transistor so the LED is on.

41. INPUT PROCESS OUTPUT probes transistor LED/buzzer SENSORS • INPUT-PROCESS-OUTPUT diagram for a moisture- sensing circuit.

42. SENSORS • Light sensors use a component called a light-dependent resistor (LDR) to determine the amount of current allowed through the circuit when light falls on it. • The LDR is a special kind of resistor which changes its resistance as the light level varies. • The LDR is connected to the base of the transistor.

43. SENSORS • In darkness, the LDR has a high resistance (typically 1 M), so virtually no current flows through it. The transistor is switched off. In dark conditions, no current flows into the base of the transistor so the filament bulb is off.

44. SENSORS • In bright light, the LDR has a low resistance (typically 270 ), allowing a larger current to flow. As the light level increases, the flow of current through the LDR increases, switching on the transistor. In light conditions, current flows into the base of the transistor so the filament bulb is on.

45. INPUT PROCESS OUTPUT light-dependent resistor transistor bulb/LED/buzzer SENSORS • INPUT-PROCESS-OUTPUT diagram for a light-sensing circuit.

46. SENSORS • The amount of light needed to switch on the transistor in the light-sensing circuit can be adjusted by adding a resistor between the base and negative side of the circuit. • The lower the resistor value, the greater the amount of light needed to switch on the transistor. • This arrangement of the LDR and resistor is called a potential divider.

47. SENSORS • To switch on the transistor in dark conditions and off in light conditions, the LDR and the resistor in the potential divider can be reversed by swapping positions.

48. SENSORS • For extra sensitivity, two transistors may be used. Darlington Pair for extra sensitivity (very small current can pass through

49. SENSORS • Temperature sensors use a component called a thermistor to determine the amount of current allowed through the circuit when temperature changes. • The thermistor is a special kind of resistor that changes its resistance as the temperature varies. • It is connected between the base of the transistor and the positive side of the circuit.

50. SENSORS • Workings of the type of thermistor that decreases its resistance as the temperature rises is described below and in the next slide. • In cold conditions, no current flows through the thermistor so the transistor is switched off.