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.
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.
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 is the flow of
electric charges. In most cases with everyday circuits, this is the flow
Electrons are super small. If
you look the word up in a good dictionary, electron will be defined as :
- a negative charge of 1.6022 x 10-19 coulomb
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..
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
- LED stands for Light Emitting
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:
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.
multiplication of electrons in the circuit – for every electron flowing through
the Base, 300 or so will be flowing through the Collector/Emitter.