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You must learn to recognise each of these circuit symbols below, and be able to draw them too Component Cell Symbol Control System Definition generates reaction. electrical Battery Two or more cells. Resistor Slows down components. current energy and via a chemical protects (delicate) process (input) Variable resistor A resistor whose value can be adjusted. process (input) Potentiometer A resistor whose value can be changed, with a third adjustable leg. Thermistor A resistor which changes resistance as temperature changes. As temperature decreases (gets colder) its resistance increases. input Light Dependent Resistor (LDR) A resistor which changes resistance as ambient light changes. When it gets darker the resistance increases. A transducer which converts brightness (light) to resistance (an electrical property). input VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 process Page 1 of 7 Definition Control System Light Emitting Diode (LED) A diode that only allows current to flow in one direction only and lights up when it does. output Flashing Light Emitting Diode A diode that only allows current to flow in one direction only and flashed on and off when it does. output Bi-colour Light Emitting Diode This is two LEDs which are wired back to back so it glows in one colour for current in one direction and glows another colour for current in the opposite direction. output Tri-colour Light Emitting Diode This is a combination of two LEDs with three leads (legs). There are three colours, either one or the other, or a combination of both. A popular example is red and green, which combine to give yellow. output Photo transistor A light-sensitive transistor (see transistor below). process Opto-isolator This is a semiconductor device which allows electrical signals to be transferred between circuits, devices, or systems, while maintaining electrical isolation between them. process Ammeter A meter that measures the flow of electrical current in amperes. Push to make switch (PTM) A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell. Component Symbol VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 Page 2 of 7 input Component Symbol Control System Definition Push to break switch (PTB) This type of push switch is normally closed (on), it is open (off) only when the button is pressed. This is commonly found in a fridge. input Single Pole Single Throw switch (SPST) An on-off switch allows current to flow only when it is in the closed (on) position. input Single Pole Double Throw switch (SPDT) A 2-way changeover switch directs the flow of current to one of two routes according to its position. Some SPDT switches have a central off position and are described as 'on-off-on' input Capacitor A capacitor stores electric charge. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals process Electrolytic Capacitor A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals. process Piezo crystal oscillator A transducer which converts electrical energy to sound. Diode A device which only allows current to flow in one direction. process An electronic latching switch process Thyristor VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 output (input) Page 3 of 7 Definition Control System NPN transistor A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit. process Field Effect Transistor (FET) Similar to a transistor, however, needs only a minute amount of current to switch/amplify e.g. used in a touch switch/sensor. process AND gate An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true. process OR gate An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true. process NOT gate A NOT gate can only have one input. The 'o' on the output means 'not'. The output of a NOT gate is the inverse (opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter. process Bell A transducer which converts electrical energy to sound. output Microphone A transducer which converts sound to electrical energy. input Buzzer A transducer which converts electrical energy to sound. output Component Symbol VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 Page 4 of 7 Definition Control System Loudspeaker A transducer which converts electrical energy to sound. output Lamp A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator, for example a warning light on a car dashboard. output Motor A transducer which converts electrical energy to kinetic energy (motion). output Component Voltmeter Voltage rails Symbol A voltmeter is used to measure voltage. The proper name for voltage is 'potential difference', but most people prefer to say voltage! A power supply Earth A connection to earth. For many electronic circuits this is the 0V (zero volts) of the power supply, but for mains electricity and some radio circuits it really means the earth. It is also known as ground. 555 timer IC Used in circuits to produce monostable (timer, delay) effects as well as astable (pulse generator) effects. process Operational Amplifier (OpAmp) Acts as a comparator; and Analogue to Digital Convertor (ADC); also acts as an amplifier; can be used as an extremely sensitive [sensor] switch. process VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 Page 5 of 7 Definition Control System Voltage Regulator A device that controls or maintains the voltage of an electrical circuit. process crossing of conductors This is indicates where wires cross over each other (without joining) – sometimes called a bridge joined conductors This indicates where wires are joined. You should make sure your draw the ‘blob’ so that it is quite distinct. Component Symbol VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 Page 6 of 7 You will NOT be required to draw these symbols, however, you should be aware of them as some of these appear in the specification and you are required to know their functions Definition Control System NAND gate A NAND gate can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not AND gate. The output of a NAND gate is true unless all its inputs are true. Although not required for AQA specification, it is useful to know, that from this gate, all others can be made. process NOR gate this is the opposite of an OR gate; only when both inputs are low / 0 the output is high / 1 process XOR gate similar to an OR gate, output is high / 1 only when one of the inputs are high / 1 (not both) process moisture sensor (probe) a sensor component that reacts to something become wet (NOT changes in moisture) – used for plant watering monitors, fuel level sensors, flood alarms 7 segment display displays numerals in a decimal fashion (dot-matrix displays are a more complex version) used in digital clocks, some modern car dashboards output solenoid a coil of wire around an iron core; becomes a magnet when current passes through the coil e.g. fire alarm bells, timed locks on bank vaults output terminal a contact on an electrical device or circuit Component Symbol ac supply an electric current that reverses direction sinusoidally 50 times per second (50 Hertz (Hz)) double pole double throw switch DPDT used to reverse the direction of a motor e.g. an electric drill relay an electrical switch operated by current flowing throw it e.g. switching on an mains operated heater using an Op-Amp temperature sensor circuit VLE > D&T > KS4 > GCSE Electronic Products - Cohort 2013 - 2015 input input Input process output Page 7 of 7