Cool circuits club
LED Circuits
LEDs have to be connected
the right way round. The + from the battery must go to the long lead of
the LED. They only conduct electricity in one direction.
LEDs can also break easily.
DO NOT CONNECT AN LED DIRECTLY ACROSS THE BATTERY. YOU MUST USE FINGERS OR THE
CIRCUIT BOARD AS SHOWN IN THE DIAGRAMS, OTHERWISE YOU MIGHT BREAK THE LED.
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?
Notes
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..
LEDs
- 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.
Transistors
- 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.
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.
