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Simple Output Devices TASK 1. Collect a set of Output Device cards. 2. Match each symbol to the correct name, energy change and type (digital or analogue). 3. Get it checked. 4. Complete the following table with the correct information: Symbol Name Energy Change Device Type Symbol Name bulb M Energy Change electrical Device Type light analogue motor electrical kinetic analogue buzzer electrical sound digital solenoid electrical kinetic digital Symbol Name Energy Change Device Type loudspeaker electrical sound analogue relay electrical kinetic digital Relay Switch A relay is a switch controlled by an electromagnet. A coil of wire: • carrying a current = magnet • with no current = non magnet Symbol: Relay Example of Relay Use A high voltage mains motor is switched on when switch S is closed. The small current in the 9V circuit makes the electromagnet become magnetic. This closes the switch and starts the motor. S 9V Relay 230 V a.c. M Reed Relay The reed relay uses a permanent magnet to open or close a switch. This type of relay is used in burglar alarm systems to detect when a door is opened. Experiment When the door is closed the magnet is close to the reed relay and switch S is open. When the door is opened, the magnet moves away from the relay, causing switch S to close setting off the alarm. magnet S :: .. :: .. to alarm Solenoid A solenoid is a coil of wire surrounding a metal rod. It is an electromagnetic device that moves a metal rod backwards and forwards. Examples of Solenoid Use • car central locking • safe locks • steering on radio controlled cars • railway points Light Emitting Diode (LED) LED Symbol: Energy Change: electrical light Type: digital output device (only ON or OFF). Wiring up an LED An LED only conducts when it is connected the proper way around in a circuit. electrons flow into point of triangle to light LED resistor in series LED lights LED does not light (FORWARD BIAS) (REVERSED BIAS) An LED is damaged if too large a current passes through. *** A series resistor limits the size of the current, protecting the LED from damage. *** Q1. (a) Which LED’s in the following circuits will light? LED 1 LED 3 LED 2 R R R R LED 4 (b) What is the purpose of the resistor R in the above circuits? protect the LED from damage (c) When an LED lights it is said to be LED’s (d) 1 and 3 forward biased. are wired this way. When an LED does not light it is reverse biased. Calculating Size of Resistor The resistor and LED are in series. So the voltage across the resistor and the voltage across the LED must add up to give the supply voltage. VS VR VR + VLED = VSUPPLY VLED ** not on data sheet ** 0 V Example 1 An LED can withstand a maximum current of 20 mA at 2 volts. Calculate the minimum value of resistor required when the LED is connected to a 5 V supply. V IR V ÷ I V R I R x VLED 2 V VR 5 2 3V I 20 mA 20 10 -3 A R? VR R I 3 20 10 -3 R 150 Ω Example 2 An LED can take a maximum current of 18 mA at 2.2 V. Calculate the minimum value of resistor required to protect the LED when it is connected to a 6V supply. VLED 2.2 V VR 6 2.2 3.8 V I 18 mA 18 10 -3 A R? R VR I 3.8 18 10 -3 R 211 Ω Q1. The maximum voltage allowed across an LED is 2.3 V and the current through it must not exceed 10 mA. The LED is connected to a 5 V supply. Calculate the value of the resistor R connected in series with the LED. 270 Ω Q2. An LED takes 10 mA and 1.5 V to work properly. What value of series resistor is required if a 6 V battery is used. 450 Ω Q3. An LED and resistor are connected in series to a 9 V supply. The maximum voltage across the LED is 1.8 V and the current through the LED must not exceed 12 mA. Calculate the value of resistor required to protect the LED. 600 Ω 7 Segment Display 7 rectangular LED’s are arranged as follows to give a 7-segment display. a f e b g The number 3 is displayed by lighting segments a, b, c, d and g c d Energy Change: electrical light Type: digital output device (segment ON or OFF). Experiment 1 – Making Numbers Using a 7-segment display, display each number from 0 – 9 in turn completing the table below. Digit Segments Lit 0 abcdef 1 bc 2 abged 3 abcdg 4 fgbc 5 afgcd 6 afedcg 7 abc 8 abcdefg 9 abcfg Experiment 2 - Making Letters Make as many letters as you can on the 7-segment display completing the following table. Letter A Appearance Segments Used abcefg Which Output Device? Selecting Output Devices Here is a list of output devices: buzzer, lamp, motor, relay, solenoid Which output device could be used to: (a) indicate required cooking time for oven is complete (b) move conveyor belt at supermarket (c) stop and start movement of conveyor belt at supermarket. buzzer motor relay Q1. Give a suitable output device for each of the following situations: (a) an audible warning when an incubator become too hot or cold buzzer (b) a power on indicator for a stereo (c) switch on a high current circuit using a small relay current (d) indicator of which TV channel is selected (e) to push chosen sweets to hatch in a vending solenoid machine (f) run a conveyor belt around a bottling factory. LED 7-seg. motor Binary Numbers just in same way as we represent decimlas by Binary numbers consist of a series of 0’s and 1’s. Consider the binary number 1101. continue to increase (double) 8 4 2 HTU 1 789 1 1 0 1 means 1 lot of 1 means 1 lot of 8 means no lots of 2 means 1 lot of 4 So we have as a decimal number: 8 + 4 + 0 + 1 = 13 ** You must know the binary for numbers from 0 to 9 ** Decimal Binary 8 4 2 1 0 0 0 0 0 1 0 0 0 1 2 0 0 1 0 3 0 0 1 1 4 0 1 0 0 5 0 1 0 1 6 0 1 1 0 7 0 1 1 1 8 1 0 0 0 9 1 0 0 1 Q1. Q2. Copy and complete the table of decimal and binary numbers: Decimal Binary 2 0010 7 0111 15 1111 18 10010 23 10111 What decimal number is represented by the binary number: (a) 0100 4 (b) 1001 9 Relay