BTC108 1 Introduction To Electronics 1
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  • 1. Lecture 1 Introduction to Electronics 1 James Uren BTC108 Electronics
  • 2. Lecture 1 Introduction to Electronics 1 What is Electronics? Using electricity to move and process information… Atoms Atoms are the fundamental building blocks of matter. They consist of a nucleus containing a number of protons and neutrons, and electrons that orbit the nucleus. The number of protons, neutrons and electrons defines the element of the atom and hence the material and its properties. In some materials the structure of the atoms (the lattice) is such that the electrons are free to move between atoms. How free the electrons are defines how well that material will conduct electricity. The term semi-conductor describes an element whose conductivity changes under certain conditions. The most commonly used semi-conductor is Silicon, and forms the foundation of digital electronics and computing. Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 2
  • 3. Charge Each electron has a charge associated with it, Q, and it is the movement of this charge that causes the electric current. Charge is measured in Coulombs (C). The charge of a single electron is tiny – 1 Coulomb is the charge of 6,250,000,000,000,000,000 (6.25 x 1018) electrons. What is the charge of 1 electron? See page 8 of this handout for notes on writing numerical answers in electronics. Current Electric current, I, measured in Amps (A), is the speed of flow of electrons. The faster the electrons move, the higher the current: Where I is the current in Amps (A), Q is the charge in Coulombs (C) and t is the time in seconds (s). How long does it take for 100 electrons to go past a point in a circuit with a current of 10mA? Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 3
  • 4. Voltage Voltage, V, also called potential, is the energy difference that causes the electrons to flow round the circuit. It is measured in Volts (V). A battery, for example, has a potential difference across it, so if the two ends are connected via an electronic circuit, a current will flow through the circuit. A useful analogy is to image that a marble on a flat surface. Lifting one end will cause the marble to roll down the slope. This example schematic (circuit diagram) shows a voltage source connected to a light bulb: + 12V Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 4
  • 5. Practical - Make and test your power cable. Read the Health and Safety Information on page 10. Through this electronics course you will be building up a circuit on stripboard (also called ‘veroboard’). Your circuit will be powered from a bench power supply, but you will need to connect this to your circuit via a power cable. The power cable should consist of red (positive) and black (negative) cable to a two-way Molex KK crimp housing. The mating header should be soldered to the stripboard. Test your power cable by taking a voltage measurement (using a Voltmeter) across the stripboard. Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 5
  • 6. Resistance The freedom of electrons in a material defines the amount of electric current that will flow through the material. This property is known as Resistance, R, measured in Ohms (Ω) i.e. the material’s resistance to current flow. A Resistor is a passive electronic component with a stable and predictable resistance. It has the following schematic symbols: OR Resistors come in a range of values, and multiple resistors can be combined to create other values. The resistor will have a tolerance associated with it given as a percentage that describes the range of acceptable resistances, i.e. how close your resistor could be to the intended value. The resistor’s value and tolerance can be read from coloured rings on the resistor itself. See page 9 of this handout for the resistor colour codes. Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 6
  • 7. Ohm’s Law Ohm’s Law relates the voltage, current and resistance in an electronic circuit: I + V R Ohm’s Law: Where V is the voltage in Volts (V), I is the current in Amps (A) and R is the resistance in Ohms (Ω). What voltage would be required to achieve 3mA through a 5kΩ resistor? In a 5V circuit what would be the current through a 1kΩ resistor? Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 7
  • 8. Practical: Measuring Voltage, Current and Resistance Read the Health and Safety Information on page 10. This practical shows three methods of finding the resistance of a resistor. Compare your answers. • Find the resistance and tolerance from the rings on the resistor body • Use your digital multi-meter to measure the resistance • Measure the voltage with a voltmeter and the current with an ammeter and use Ohm’s law to find the resistance. Schematic: + A V R Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 8
  • 9. Writing Numerical Answers Decimal Places Giving an answer to 3 decimal places means three digits after the decimal point. If the 4th decimal place is 5 or above, round up the 3rd decimal place. e.g. 65.342545 given to 3 DPs is 65.343 Significant Figures Giving an answer to 3 significant figures means showing only the 3 left-most digits (rounding in the same way. e.g. 65.342545 given to 3 SFs is 65.3 768593.25 given to 3 SFs is 769000 3 significant figures is normally enough information in electronics. Give all answers to this accuracy unless directed otherwise. Units For large and small numbers it is convenient to use an exponential notation with 10 - ‘to the power’ - X. e.g. 768593.25 expressed in this way and to 3 SFs is 7.69 x 105 For the following cases this is simplified: p pico x10-12 n nano x10-9 μ micro x10-6 m milli x10-3 k kilo x103 M mega x106 G giga x109 T tera x1012 e.g. 768593.25 can be expressed (to 3 SFs) as 769 k or 0.769 M. Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 9
  • 10. Black Brown Red Orange Yellow Green Blue Purple Grey White Sourced from showcase.netins.net Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 10
  • 11. Health & Safety Considerations Soldering and de-soldering: Solder melts at between 180 and 200°C. Soldering irons will heat up to between 250 and 400°C. Be extremely careful when soldering and take the following precautions: • Switch off the soldering iron at the mains when not in use • Always keep the iron in its stand • Make sure your workspace is clear, well lit and well ventilated • Never solder while your circuit is powered up • Never solder without tutor supervision • Only apply the soldering iron for the minimum amount of time • Keep your soldering tidy and use the minimum amount of solder • Avoid breathing in solder fumes • You must only use the lead-free solder provided • You must use tools e.g. pliers to support components that are being soldered and ensure the board is secure. Switching it on: Powering up a circuit that is incorrectly connected can cause components or equipment to get extremely hot or even ‘blow’. A short circuit (where unintended electrical connections are made) for example may damage equipment or blow components causing them to behave in an unpredictable way. • Before powering up your circuit you MUST have it checked by the tutor • Have your neighbour physically inspect your work before powering on • If your circuit does not behave as you expect, switch it off immediately • Use your nose! A faulty circuit with hot components will often smell or smoke Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 11
  • 12. Testing and fault-finding: If your circuit does not behave as you expect: • With the power off, confirm by eye that your circuit is connected correctly and that you are using all the correct components and mounted with the correct polarities • Inspect your circuit closely for short circuits, soldering faults and dry joints: • Do all the testing on your circuit that you can with it powered off. • Be extremely careful when probing your circuit live as the probe itself can cause short circuits • When probing with an oscilloscope ensure the earth connection is applied safely Lecture 1: Introduction to Electronics 1 BTC108: Electronics – James Uren 12