EMS1EP Lecture 2Electronic 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 = I x RV: 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
Images from: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html
sand filter
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
INPUT OUTPUT0 11 0
Truth table
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
INPUT 1
INPUT 2
OUTPUT
0 0 0
0 1 0
1 0 0
1 1 1
Truth table
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
INPUT 1
INPUT 2
OUTPUT
0 0 0
0 1 1
1 0 1
1 1 1
Truth table
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)
INPUT 1
INPUT 2
OUTPUT
0 0 0
0 1 1
1 0 1
1 1 0
Truth table
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