Electronics / Modelling in Livewire & PCB Wizard Automatic Switching:- Light / Temperature Sensing - Transistor Projects. R.A. Moffatt.

Automatic Switching: Transistor Project Aims: To understand the concept of automatic switching / sensing in electronic circuits To practice modelling basic electronic switching circuits using the Live Wire and PCB Wizard software To construct (PCB’s) printed circuit boards

Automatic Switching: Transistor Project You will have an opportunity to:- Design a temperature/light sensing circuit. To manufacture a printed circuit board. Two of the circuits respond to a change in light levels and the other two respond to a change in temperature levels.

Practically every modern Intel Pentium processor main board features a temperature sensor developed at Delft University of Technology. The sensor detects when the processor starts to become too hot, and switches on a fan to cool it down. As soon as the temperature drops to an acceptable level, the fan is switched off. The temperature sensor was developed by Dr. Anton Bakker, who in April 2000…

Our Learning Intentions know how to use the Live Wire and PCB Wizard software how to design automatic control circuits understand input sensors and transistor switching an understanding of resistor colour codes using four and five band resistors circuit building skills developed by using the soldering iron practice at following detailed test procedures

WALT Electronics We Are Learning To To understand the concept of a potential divider which provides automatic switching of electronic circuits This is because .. We can learn how to design electronic circuits and systems using automatic switching for our project work Remember to: refer to the water analogy to help understand how the Potential divider works

What I am Looking For WILF: Electronics an understanding of the potential divider as a sensor / automatic switch the ability to sketch a circuit diagram of an automatic temperature / light sensing sensor circuit to be able to model and test an automatic switching circuit to make a PCB and build a sensing circuit as an example of a transistor-based control system

Potential Divider Single-Pole-Single-Throw Switch Preset – Variable Resistor Component symbols Light Dependant Resistor 0V Potential Divider

The Potential Divider Water Pipe Analogy: X B Y Diagram extracted from Making Things Work by Ken Shooter & John Saxton

The Transistor Transistors are semiconductor devices. This means that they have a resistance to the flow of electrons – current. However they become conductors if a small voltage is provided across two of the legs – the base and the emitter. Collector (c) Emitter (e) Base (b) Symbol for the n-p-n transistor You can use the transistor as a high speed switch if a small voltage of 0.6 – 1.6V is applied to the base leg as shown below Technology Education Centre 05.

The Transistor Large Voltage C 9V B 0.6V E Saturated = ‘fully on’ PNP Transistor B C E Small Voltage in symbol Saturated = ‘fully on’ http://www.satcure-focus.com/tutor/page4.htm

hfe = Ic Ib hfe Transistor Gain: We know that a small current flowing at the base of the transistor will ‘turn on’ a large collector current. This is known as current Amplification. The ratio I I is a measure of the amplification which we call the transistors current gain. The symbol for the transistor current gain is c b hfe hfe = Ic Ib (0.00025A) (0.05A) = 0.5 A 0.00025 A = 200

The Transistor http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/page1.html

http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

Bulb-’off’ when Dark BULB ‘off’ LDR Transistor V/Resistor

Bulb-’on’ when Light BULB ‘on’ V/Resistor Transistor LDR

LED-’off’ when Light shines on LDR VR Transistor LDR

LED-’on’ when Dark

Ex 1: Potential Divider / Dark Light ‘on’ In the light the voltage between the base and the emitter leg of the transistor is 657mV or 0.65V. For this transistor the voltage is not enough to switch it on – therefore the bulb remains off. ‘OFF’ In the darkness the voltage between the base and the emitter leg of the transistor is 739mV or 0.739V. This voltage is high enough to switch on the transistor – therefore the bulb is switched ‘on’. EX: 10 ‘ON’ Model the circuit using Live Wire as shown and test! Draw this circuit diagram in your folder and explain how it works?

Ex 2: Dark Sensor: Circuit 4 from 112 Circuit Designs – M. Lynch TIP 121 Light level low LED will be ‘on’ Model this circuit and test using Live Wire Draw this circuit diagram in your workbook and explain how it works? Convert this circuit to a PCB layout using PCB Wizard

PCB: Printed Circuit Board Real World Normal PCB Wizard

Printed Circuit Board

Circuit 5 A Light Sensing Transistor

Play the AVI file to help understand how this circuit works? M. Lynch Play the AVI file to help understand how this circuit works?

Double-Click the PDF icon to access the data sheet House plants can suffer if owners do not give them the right amount of water. Houseplants can die if they do not receive enough water, and they can rot if over watered.

Moisture Tester ‘on’ moisture level

Darlington Pair Driver In a Darlington pair circuit, two transistors are wired together to provide better Switching.

Electronics Year 9 Test Make sketches of a 1K, 2k2, 680R and 470R resistor include the colour code for each Explain the function of a resistor in an electronic circuit? Draw the two component symbols necessary and in the correct order to make a potential divider that sounds a buzzer when light shines on the LDR? One of these component symbols have been drawn for you.

4) Explain how the circuit shown below works? 5) Suggest two uses for this type of circuit? 6) What is the trigger voltage for a BS 108 Transistor? 7) Sketch the symbol for a transistor and label the legs: - emitter, collector, base

8) An electronic sensor is required for an elderly persons room that sounds an alarm when the room temperature drops to a certain level or gets ‘too cold’. Draw and complete the circuit diagram using symbols to show the type of sensor required? 9) Name each of the components used in your design?

10) Name each of the component shown below and explain briefly their function when used in an electronic circuit?

http://www.circuitspecialists.com/prod.itml/icOid/8181 http://www.new-wave-concepts.com/br_files.html