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Electronic Projects

If you have ever looked inside a computer, mobile phone or other electronic equipment, you will see lots of square or rectangular black or grey things, sometimes with lots of very small metal legs coming out of them. Many people know these are called micro-chips. They have other names - ICs, Integrated circuits, chips, silicon chips and more... However, what you are looking at is just the outside packaging. Inside these chips are very sensitive small electronic circuits. Below is a picture of an old Intel chip of. Its actuall size is only about 5mm x 5mm. .


Picture of the chip inside an Intel 8086

What you can see are the connections making up the circuits and joining different circuits together. What the circuits are mainly joining together are transistors. Transistors can be thought of as small electrically controlled switches that can be joined together to make complicated circuits. The transistors can be very very small - about 1/1000000 or a metre. In a simple modern memory card, you can get 1000 million easily in a something smaller than a postage stamp.

The projects we will do later use single transistors. But to start with, we will use some other everyday electronic components called LEDs. LEDs look a bit like small light bulbs, but they are much more complicated than that. They are very modern and use very complicated modern physics and maths to design them. Check out the LED projects to see what can be done easily with LEDs.



Pencil PCB

You can make your own printed circuit board PCB using a pencil and some thick card. the carbon or graphite in the pencil conducts electricity. If you make a continuous pattern on some card, you can make a circuit light up an LED. BUT the lines must be thick and they must be continuous! See the examplebelow:


The carbon in pencils conducts electricity. Make sure the lines are thick.



Transistor Circuits
The leads on the transistor must be connected correctly. The picture show the transistor from the bottom where the leads come out from.



Which LED is brighter? What is the transistor doing?




Electricity and Electronics


  • Electricity is the flow of electric charges. In most cases with everyday circuits, this is the flow of ELECTRONS.
  • Electrons are super small. If you look the word up in a good dictionary, electron will be defined as :
    • A lepton with
      • a negative charge of 1.6022 x 10-19 coulomb
      • Rest mass 9.1096 x 10-31 kilogram
      • Radius 2.818 x 10-15 metre
      • Spin ½
These are unusual words with very specific meanings. Until these characteristics were well understood, electronic components could not be made.
  • There are an incredibly large number of electrons flowing through the wires in a second – about 100,000,000,000,000,000 or so..
Electronic components take advantage of the characteristics of electrons to allow them to be controlled. Therefore, electronic devices could not be made until we understood well what electrons were and how they reacted to outside effects. Thus, electronic components such as LEDs and Transistors are very recent inventions of the last 50 years or so. Improvements are consistently being made to improve the efficiency and to reduce the size of components. New materials are constantly being developed to create new components that give new effects and uses – eg the blue LED has been developed extensively in only the last ten years..
  • LED stands for Light Emitting Diode
  • Diodes only conduct electricity in one direction.
  • To connect properly, connect the positive or + side of the battery to the LONG lead of the LED.
  • Directly connecting an LED across a battery can break the LED. It can get hot, and so can the battery. The LEDs used will tolerate a few seconds of direct connection. However, the circuits have been designed to use the fingers or the carbon circuit board to limit the current flowing. To minimise the number of components, extra current reducing resistors have not been used. See the web site for alternative circuits.
  • Some modern LEDs are so sensitive and efficient that they will glow even from the small amount of electricity that can flow through a person using a 9volt battery
  • The more electrons that are flowing through the LED, the brighter it will be.
  • The transistor being used has three terminals called:
    • Base
    • Emitter
    • Collector
  • Transistors can be considered as switches or amplifiers or multipliers.
  • Multipliers are probably the easiest word for most people to understand. The number of electrons flowing through the base is amplified or multiplied by the gain of the transistor. This result is then how many electrons will flow through the collector and the emitter (almost)..
  • The gain of a transistor is a characteristic of each transistor, based on its fabrication style and parameters. The BC108 transistor being used has a gain of about 300. So for every electron that flow through the base, about 300 will flow though the collector/emitter part of the circuit.
  • In the transistor circuits, you can see that the transistor has amplified the number of electrons flowing through your fingers or PCB, because of the difference in the brightness of the two LEDs in the circuit.
Example of multiplication of electrons in the circuit – for every electron flowing through the Base, 300 or so will be flowing through the Collector/Emitter.



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