Transcript Slide 1

EMS1EP Lecture 2
Electronic Circuits
Dr. Robert Ross
Overview
(what you should learn today)
•
•
•
•
Ohms law
Voltage/Current/Resistance
Analog/Digital
Breadboards
Voltage/Current/Resistance
• Three important
quantities in electronics
• Related by Ohms Law:
V=IxR
V: Voltage (Volts)
I: Current (Amps)
R: Resistance (Ohms)
• How many Amps flow
through this circuit?
Hydraulics Analogy
• These quantities are based on electrons which
are very small and hard to see
• A nice (but not perfect) analogy can be made
with a closed hydraulic system
sand
filter
Images from: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html
Voltage
• Measured in Volts (V)
• Is the ‘electric potential’ between two points
– “Voltage is the work done per unit charge against
a static electric field to move a charge between
two points”
• Common sources: Power supply, battery,
power point
• Like the water pressure in the hydraulics
analogy (this is supplied by a water pump)
Current
• Measured in Amps (I)
• Is the flow of electric charge through a circuit
– Typically the flow of electrons through a wire
• Like a the water pump in the hydraulics analogy which
provides water pressure
• DC (Direct Current): Current only flows in one direction
• AC (Alternating Current): Current changes direction at a
determined frequency
• For Hydraulics analogy – like the flow-rate
– More water flowing through pipe = higher flow-rate
– More electrons flowing through circuit = higher current
Resistance
• Measured in Ohms (Ω)
• Opposition to the passage of current flowing through
a conductor
• Wire has low resistance so it is a good conductor
• We use resistors to introduce resistance of a defined
amount into a circuit
– e.g. to limit the current to an LED to control the brightness
• Hydraulics analogy – Sand filter decreases
water flow
Resistor colour codes
• The colours printed on
the sides of the
resistors specify the
value
• What would the
following resistors be:
Review
A circuit therefore has:
• Different voltages
between different points
• Current flowing through it
(pushed on by the
voltage)
• Resistances which restrict
the flow of current
• These are all related by
Ohms law
Image from: http://www.sengpielaudio.com/calculator-ohmslaw.htm
Analog/Digital
• Common perception:
– Digital is all about 0’s and 1’s
– Analog is something different not using 0’s and 1’s
• In electronics:
–
–
–
–
Digital is where only two voltage levels are used
One voltage (e.g. 0V) represents a ‘0’
Another voltage (e.g. 5V) represents a ‘1’
This is based on a number system called binary (values can
only be ‘0’ or ‘1’
– Analog is where voltages follow a continuous value (not
two prescribed values)
Analog/Digital
• Analog Voltages: Continuous voltages
• Digital Voltages: Discrete voltages
Digital Revision – Analog/Digital
• Analog Voltages: Continuous voltages
• Digital Voltages: Discrete voltages
Digital Logic Voltages
• Digital electronics is an abstraction of analog
electronics
• Typically we select two voltages and label one
as low (typically 0V) and one as high (1.2V,
1.8V, 3.3V, 5V ect)
• In Ardiuno-land we normally talk as:
– Low = 0V
– High = 5V
Why is digital useful?
• Allows us to do logical computations and
comparisons between different binary
numbers
• If this were all analog (using continous
numbers) this becomes difficult for us to
design and program
• In digital domain very easy to program by
writing code
Digital Revision – Number Systems
• Computers use binary (base 2 number system)
• Humans like to use decimal (base 10 number system)
• Hexadecimal (hex) is a nice way of displaying binary
numbers
• Notations:
– Binary: 01010010b or 010100102
– Decimal: 212 or 21210
– Hex: 0x31 or 31h or 3116
• When you write code – the compiler doesn’t understand
the subscript 2, 10 or 16, so just use the first notation
• In later maths and electronics subjects you will be
required to calculate back and forth between number
systems.
Logical Binary Operations
• There are a number of basic logical operations
that we can easily perform on binary
numbers:
– NOT
– AND
– OR
– XOR
Logical Operations: NOT
• This operation inverts (flips) a binary bit
– Changes 0->1 and 1->0
• We can do this in code by using:
– ~ (tilde) for inverting each bit in a value separately
or
– ! for changes the value from 0->1 / 1->0
• There is also some electronic hardware (inverter or
NOT gate) which also does this on an individual bit
• Symbol:
Logical gates: NOT
Truth table
INPUT OUTPUT
0
1
1
0
Logical Operations: AND
• If all the inputs are ‘1’
then the output will be
‘1’
– 1 AND 1 => 1
– 0 AND X => 0
• In programming: & and
&& symbols
Truth table
INPUT 1 INPUT 2 OUTPUT
0
0
1
0
1
0
0
0
0
1
1
1
Electronic Symbol
Logical Operations: OR
• If any of the inputs are
‘1’ then the output will
be ‘1’
– 0 OR 0 => 0
– 1 OR X => 1
• In programming: | and
|| symbols
Truth table
INPUT 1 INPUT 2 OUTPUT
0
0
1
0
1
0
0
1
1
1
1
1
Electronic Symbol
Logical Operations: XOR
• If the inputs are
different then outputs
will be ‘1’
– X XOR X => 0
– X XOR NOT(X) => 1
• In programming: ^
(caret)
Truth table
INPUT 1 INPUT 2 OUTPUT
0
0
1
0
1
0
0
1
1
1
1
0
Electronic Symbol
Windows Calculator
• Switch to ‘Programmer
mode’
• Has HEX, DEC, OCT and
Binary number systems
• Allows you to convert
back and forth and
perform computations
• Shortcut: use Function
keys (F5, F6, F7 and F8)
Breadboards
• Breadboards (AKA: White
chocolate boards)
• Good for prototyping low
frequency circuits
• Very quick to construct and
reconfigure circuits by
plugging in wires
• We use these in the labs for
prototyping circuits
Using Breadboards
• The holes are
connected as follows:
– The holes on the sides
are connected
vertically (use for
power and ground
connections)
– The holes in the
middle are connected
horizontally (use to
build your circuit)
Using Breadboards
Summary
(What you learnt in this session)
• Ohms Law
– Voltage, Current and Resistance
• Analog and Digital
• Breadboards