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