Unit 1 Electronics Name: Form:

Transcription

1 Unit 1 Electronics Name: Form:

2 Electronics Electronics is the study of components and techniques used to be able to build circuits controlled by electricity. An electronic system uses discrete components. Any electronic system is made up of three parts. Input Transducer Process component Output Transducer The relationship between these parts is governed by the different variables, Voltage, Current and Resistance. Batteries D C AA AAA PP3 Batteries provide the circuit voltage. Voltage is the driving force. It provides the circuit with electrical energy. Batteries store this electrical energy. Battery Cells are described by their physical size, for example D or C or AA or AAA or PP3 which are the most common. In Systems and Control we tend to use AA battery cells to power the circuits. Battery Cells are also described by the amount of voltage they provide. D, C, AA, AAA battery cells provide 1.5 Volts. PP3 batteries provide 9Volts. The symbol for a single battery cell can be seen below. + Single Cell Battery 2

3 More than one battery cell can be connected together to provide a higher voltage battery. Most circuits we design will use 6 Volts. What if I need 6 Volts? How many AA battery cells does it take to make 6Volts? Calculate your answer here. This battery can be drawn like this: +6V Note the dotted line to show that more than one cell is being used. Battery cells can be connected easily together in a battery cell holder. Research Tip These can be ordered from RAPID ELECTRONICS but there are many other types available too. 3

4 Batteries How do I know if I am choosing the right battery? 4

5 Electronic Units V, I and R What is Voltage? Voltage is the electro motive force of any circuit and is measured in Volts. A battery cell has two main specifications: Physical size for example AA Voltage for example 1.5Volts They can be connected together in series. Rapid Electronics provide battery holders for your projects. What is Current? If voltage is a force then current is a flow. Current is the amount of electrons flowing around the circuit being provided by the battery cells. What is current measured in? Current is measured in Amperes shortened to AMPS. +6V Conventional current flows out of the battery positive (RED) terminal through a circuit and back to the negative (BLACK) terminal. A circuit will resist the flow of this current, and therefore we can control the amount of current flowing around a circuit. Colour in the POSITIVE and NEGATIVE wires the correct colours POSITIVE, +Ve connection will be RED +6V NEGATIVE, -Ve connection will be BLACK 5

6 What if I need to draw a Circuit Diagram? How can I remember to draw a circuit diagram? Steps to drawing a circuit diagram 1. Start with a battery and draw this on the left hand side of your page. 2. Next add in +Ve Volts supply rail at the top of the space 3. Leave a reasonable gap 4. Then add the Ve supply rail at the bottom of the space 5. Now add your input component 6. Next is the process component 7. Finally add in your output component. 8. Now draw in the wires to connect your circuit MNEMONIC = Bat Rail + Gap IN Proc Out Wires [BR+G-IPOW] Can I draw a series circuit that uses two switches and lights up a LED, remember an LED needs a resistor? Specifications: Use a 6V battery Use two push button switches Use a 330Ω resistor HINT SERIES: Eastenders is a series 6

7 Can I follow the steps again and draw a parallel circuit to light up an LED when one of two switches is pressed. Specifications: Use a 6V battery Use two push button switches Use a 330Ω resistor HINT: Parallel: A ladder is parallel 7

8 Therefore this resistor is 1000 Ω FACTOID What if I get electrocuted? Did you know it only take 0.03A to flow across your heart to cause it to stop beating? That s 3 100ths of an AMP! A Vacuum cleaner uses 8 Amps to work! Why do batteries go flat? When designing a circuit check that the batteries used will provide enough current for your circuit. What is Resistance? FACTOID: A resistor will resist or limit the flow of current around a circuit. They can be used to SET a particular voltage needed in a circuit. Resistors are measured in OHMS, which has the symbol Ω. Resistors DO NOT STOP the flow of current. Each resistor has a particular colour code that tells us its resistance. How can I work out its resistance? Here is the key. Colour Colour Band 1 Colour Band 2 Colour Band 3 Tolerance Black 0 0 nothing Brown Gold = +/- 5% Red Orange Silver = +/- 10 % Yellow Great Blue Violet Grey White ALWAYS read the resistor left to right with the tolerance band on the RIGHT Brown Black Red Gold Band 1 Band 2 Band 3 Tolerance /- 5%

9 Can you decode the resistors below USE A PENCIL 1 Brown Black Orange Gold 2 Brown Red Red Gold 3 Yellow Violet Black Gold 4 Orange Orange Brown Gold 5 Red Red Red Gold Now work back wards. Assume the tolerance band +/-5% 6) 27KΩ. Band 1 = 2 Band 2 = 7 Band 3 = K and K is 000 (1Kg is 1000grammes likewise 1KΩ = 1000 Ohms. 2 = RED, 7=Violet, 000 = Orange Answer = RED VIOLET ORANGE GOLD 7) 100KΩ 8) 15Ω 9) 270Ω 10) 18KΩ 9

10 Draw and colour the following resistors all with a tolerance of +/-5%: 1. 1KΩ 2. 22KΩ Ω 4. 10KΩ 5. 4K7Ω 10

11 Ohm s Law Ohm s law states the relationship between current (I measured in Amps), voltage (V measured in Volts) and resistance (R measured in Ohms Ω) in any electrical circuit. It is given as: V = I x R R = V I I = V R So if we know two of these we can work out the other one. Question: Work out the value of the resistor R in the circuit below. +6V 2A R Ω What do we know? V = I = R = Which formula shall we use? R = V I Substitute in the values. R = 6 2 R = 3 Amps 11

12 Calculate the missing value +V 1A What is V? Put you workings here. 100 Ω +6V I What is I? Put you workings here. 60 Ω +4V 0.02 What is R? Put you workings here. R 12

13 Designing using Ohm s Law I need a resistor to limit the current flowing in an LED because the maximum an LED can take is 0.02A, any more and it will break. When an LED is switched on it will drop 2Volts across itself. This is the voltage needed to push the electrons through the LED. So a circuit with an LED will look like this. +6V R Ω 0.02A 2V V measured across R = 6 2 = 4Volts I flowing through R = 0.02A Therefore R = V I R = R = 200 Ω If you are using LEDS In your coursework put this calculation in to prove you know how to design the value of correct resistors for your circuit. Research Tip 13

14 Design a series circuit to switch on 2 LEDS using a 9Volt battery and a DPDT toggle switch. Step 1 Draw the circuit diagram. Step 2 Calculate the resistor needed for the circuit. Build your circuit on a breadboard. 14

15 Self Assessment Quiz 1-10 minutes maximum 1 Match the following symbols with the correct names: + Battery cell Resistor LED 2. Calculate the Voltage in a circuit when I = 2 Amps and R = 220Ω 3. The current flowing through an LED has a limit, what is that limit? 4. What is resistance measured in? 5. Using the resistor colour code what colour bands would be found on the following, assume a tolerance of GOLD? 1K Ω 220 Ω 390 Ω 22K Ω 10K Ω 15

16 How do you connect up a sensor? A sensor is a clever bit of technology; which uses a smart material. A sensor will detect a change in something and respond to that change in some way. Think of an LDR. It responds to changes in light. Think of a Thermistor. It responds to changes in temperature. But a component on its own is no good. It needs to be connected into a circuit. That s where a potential divider circuit is used to make use of these changes. 16

17 What If What if I connected an LED in series with an LDR would it light up when it got dark? Why. Write a question you have about the circuit here 17

18 Potential Divider Circuits Two resistors connected in series will work as a potential (voltage) divider. +6V 1KΩ Multimeter set to 20V DC scale 6V 1KΩ 3V Try it using a bread board, 2 1K resistors, and a multimeter. Multimeter Breadboard 18

19 Bread Boards A breadboard allows you to model your circuit without the need for solder. It consists of holes with copper strips underneath to connect the components. The holes are therefore connected together as shown by the lines on the picture. So your potential divider system would look like this. RED 1K Components connected inside the breadboard 1K BLACK 19

20 Using a Multimeter to test for DC Voltage DC Range RED BLACK Set up this circuit on the Breadboard and measure V1 +6V 10KΩ Multimeter set to 20V DC scale 6V 22KΩ V1 My V1 measurement is : Volts 20

21 Crocodile clips Circuit for potential divider 21

22 Designing a Potential Divider Circuit Vs If Vs = 6 Volts and Rtop = 10K and Rbot = 22K Rtop Then we can use this formula to calculate the Voltage across Rb(bot) VR b = Vs x Rbot Rtop + Rbot Rbot VR b = 6 x VR b = 6 x VR b = 6 x VR b = Volts Your Turn Calculate V Rb in the circuit below 6V Show your workings here 100K 1000K 22

23 Self Assessment Quiz 2-10 minutes maximum What is a breadboard when used in electronics? Which range would you use on a Multimeter to measure a battery? Use a ruler to draw a potential divider circuit with Vs = 9V, Rt = 22K and Rb = 68K. Calculate the Voltage across Rb in your potential divider circuit. 23

24 Input Transducers The start of any system is the input. Input Transducer Process component Output Transducer Find the symbols for each of the transducers listed below and add them to the mind map. 24

25 The microphone This component converts sound into electrical energy to send an ANALOGUE signal to the process component. Electrical Symbol for Microphone ANALOGUE sound wave ANALOGUE means a device in which data is represented by continuously variable, measurable, physical quantities. ANALOGUE signals come from sound light voltage temperature position pressure Analogue is the opposite of digital. 25

26 The Variable Resistor This component converts kinetic energy into electrical energy and sends an ANALOGUE signal of position to the process component. Electrical symbol for a variable resistor. Switches These components convert kinetic energy into electrical energy and send DIGITAL signals to the process component. In systems design micro switches are used to sense the presence of doors, lids or any part of a machine to tell a process to activate/deactivate. Push button Other types of switches are used to control the power to a circuit commonly referred to as ON/OFF switches and tend to be toggle or slide switches. DPDT 26

27 Symbols for switches Switch Symbol Description Single Pole Single Throw SPST A basic ON/OFF switch Single Pole Single Throw SPST Single Pole Double Throw SPDT NC NO Push button Micro switch Double Pole Double Throw DPDT Two reversing switches in one Digital Signals A digital signal is either ON or OFF, there is no in between as with sound levels or light levels. Using BINARY a digital ON is known as a 1 and a digital OFF is known as a 0. Moisture Sensor A moisture sensor makes use of the conductivity of water. When water falls between two pieces of wire current will flow and the sensor sends a 1 signal to a process device. Is it wet? Yes or No 1 or 0 is sent to the process component Moisture sensor copper tracks Symbol: Wires to process device SAQ Is a moisture sensor a Digital or Analogue component? 27

28 Thermistor A thermistor is a resistor that changes its resistance depending on the temperature. A NTC (Negative Temperature Coefficient) thermistor will decrease in resistance as temperature rises. A PTC (Positive Temperature Coefficient) thermistor will increase its resistance with the increase in temperature. -t o +t o NTC PTC A typical response of the NTC thermistor to temperature can be seen here. This particular NTC thermistor is 25 o C However as temperature 43 o C it is 5K 28

29 LDR Light Dependant Resistor. As light levels fall so the resistance increases. A graph showing the relationship of light against resistance is shown below. Resistance Light Level (Lux) SAQ Is an LDR analogue or digital? SAQ Is a thermistor analogue or digital? 29

30 LDR experiment Measure the resistance of a LDR in complete darkness, room lights off, room lights on and bright light (use a torch), Ω Resistance complete darkness Resistance room lights off Resistance room lights on Resistance in bright light Plot and draw a graph of your results here Resistance 1MΩ 100KΩ 10KΩ 1KΩ 0Ω Light Level Dark Room lights OFF Room lights On 30 Bright

31 Connecting Input Components Input components need to be INTERFACED (joined or connected to) with process components, and to do this we need to connect them into a potential divider circuit. We can then design the Input part to any circuit. A Darkness Sensor Circuit For example: +6 10K VR b Connect up this circuit on a breadboard and measure VR b (Voltage across Resistor bottom) in complete darkness and in daylight. Bright Light (Torch) Volts Daylight reading Volts Complete Darkness Volts This arrangement of the potential divider circuit will detect darkness. If in darkness the LDR = 1,000,000 Ω Calculate VR b VR b = Vs x Rb Rt+Rb VR b = 6 x 1,000,000 1,010,000 VR b = 5.94V 31

32 A Daylight Sensor Circuit K This time you will notice a 100K Variable Resistor is used. This is to make the circuit adjustable for different levels of light. A temperature sensing circuit (HOT) NTC, when temperature increases the voltage across the variable resistor will rise. +6 -t o C 100K A temperature sensing circuit (COLD) NTC, when temperature decreases the voltage across the thermistor will rise K -t o C 32

33 Connecting Switches Switch Sensing Circuit Output when pressed This could be for micro switch, pressure mat, tilt switch or reed switch K Switch Sensing Circuit Output when NOT pressed +6 10K SAQ Input Transducers 1 Which input component would you use to detect temperature? 1 2 What component is this symbol for? 2 NC NO 3 When it gets dark the resistance of and LDR rises, TRUE or FALSE? 1 33

34 4 Circle the odd one out 1 Battery LDR Micro Switch Push Button Now give a reason why: 2 5 Circle the odd one out 1 LDR Thermistor Switch Moisture Sensor Now give a reason why: 2 6 DPDT stands for Double Press Double Touch True or False 1 7 DPDT refers to Thermistors. True or False 1 8 Draw the symbol for a SPST switch. 2 9 Make a list of FOUR digital input components 4 10 What does Analogue mean? 2 [20] 34