What is a circuit diagram and its prerequisites to understand?

What is a circuit diagram and its prerequisites to understand? The answer of this question is that:

A circuit diagram is termed as: “a visual display of an electric circuit using either industry standard symbols or basic images of parts”. It is also called as electronic schematic or electrical diagram. These (Circuit diagrams) are the milestone of each electronic device. These are used for designing, constructing and troubleshooting in an electronic circuitry.

In a circuit diagram; symbol usage is based on the audience viewing / using the diagram.

It has two major types:

1. Pictorial Circuit Diagram:

It uses basic images of components. It is designed for less technical audience as it is clear from following diagram that we have a battery as a power supply source, a resister for limiting the current value, a voltmeter for voltage measurement & an ammeter for current measurement.

2. Schematic Diagram:

It uses industry standard symbolic representation of components and their interconnections within a circuit. It is designed for a highly technical audience, especially electrical engineers or the personnel involved in troubleshooting activities.

Prerequisites of circuit diagrams:

The main prerequisite of a circuit diagram is the final analysis that which type of audience will be going to view the diagram.

By keeping in view the target audience, there are some basic technical things to be understood for better design, construction and troubleshooting.

• Symbols:

Each electric / electronic part has number of unique symbols used in circuit diagrams. So, to develop a circuit diagram; one should be first aware of symbols used for electrical instruments.

Here we have made a comprehensive table containing details of each component / instrument name, its symbol and its meaning in electrical terminology.

Mostly used Electrical Symbols

Symbol	Component name	Meaning	Real world example
Wire Symbols
	Electrical Wire	Conductor of electrical current
	Connected Wires	Connected crossing
	Not Connected Wires	Wires are not connected
Switch symbol
	SPST Toggle Switch	Disconnects current when open
	SPDT Toggle Switch	Selects between two connections
	Pushbutton Switch (N.O)	Momentary switch – normally open
	Pushbutton Switch (N.C)	Momentary switch – normally closed
	DIP Switch	DIP switch is used for onboard configuration
	SPST Relay	Relay open / close connection by an electromagnet
	SPDT Relay
	Jumper	Close connection by jumper insertion on pins.
	Solder Bridge	Solder to close connection
Ground Symbols
	Earth Ground	Used for zero potential reference and electrical shock protection.
	Chassis Ground	Connected to the chassis of the circuit
	Digital / Common Ground
Resistor Symbols
	Resistor (IEEE)	Resistor reduces the current flow.
	Resistor (IEC)
	Potentiometer (IEEE)	Adjustable resistor – has 3 terminals.
	Potentiometer (IEC)
	Variable Resistor / Rheostat (IEEE)	Adjustable resistor – has 2 terminals.
	Variable Resistor / Rheostat (IEC)
	Trimmer Resistor	Preset resistor
	Thermistor	Thermal resistor – change resistance when temperature changes
	Photoresistor / Light dependent resistor (LDR)	Photo-resistor – change resistance with light intensity change
Capacitor Symbols
	Capacitor	Capacitor is used to store electric charge. It acts as short circuit with AC and open circuit with DC.
	Capacitor
	Polarized Capacitor	Electrolytic capacitor
	Polarized Capacitor	Electrolytic capacitor
	Variable Capacitor	Adjustable capacitance
Inductor / Coil Symbols
	Inductor	Coil / solenoid that generates magnetic field
	Iron Core Inductor	Includes iron
	Variable Inductor
Power Supply Symbols
	Voltage Source	Generates constant voltage
	Current Source	Generates constant current.
	AC Voltage Source	AC voltage source
	Generator	Electrical voltage is generated by mechanical rotation of the generator
	Battery Cell	Generates constant voltage
	Battery	Generates constant voltage
	Controlled Voltage Source	Generates voltage as a function of voltage or current of other circuit element.
	Controlled Current Source	Generates current as a function of voltage or current of other circuit element.
Meter Symbols
	Voltmeter	Measures voltage. Has very high resistance. Connected in parallel.
	Ammeter	Measures electric current. Has near zero resistance. Connected serially.
	Ohmmeter	Measures resistance
	Wattmeter	Measures electric power
Lamp / Light Bulb Symbols
	Lamp / light bulb	Generates light when current flows through
	Lamp / light bulb
	Lamp / light bulb
Diode / LED Symbols
	Diode	Diode allows current flow in one direction only – left (anode) to right (cathode).
	Zener Diode	Allows current flow in one direction, but also can flow in the reverse direction when above breakdown voltage
	Schottky Diode	Schottky diode is a diode with low voltage drop
	Varactor / Varicap Diode	Variable capacitance diode
	Tunnel Diode
	Light Emitting Diode (LED)	LED emits light when current flows through
	Photodiode	Photodiode allows current flow when exposed to light
Transistor Symbols
	NPN Bipolar Transistor	Allows current flow when high potential at base (middle)
	PNP Bipolar Transistor	Allows current flow when low potential at base (middle)
	Darlington Transistor	Made from 2 bipolar transistors. Has total gain of the product of each gain.
	JFET-N Transistor	N-channel field effect transistor
	JFET-P Transistor	P-channel field effect transistor
	NMOS Transistor	N-channel MOSFET transistor
	PMOS Transistor	P-channel MOSFET transistor
Misc. Symbols
	Motor	Electric motor
	Transformer	Change AC voltage from high to low or low to high.
	Electric bell	Rings when activated
	Buzzer	Produce buzzing sound
	Fuse	The fuse disconnects when current above threshold. Used to protect circuit from high currents.
	Fuse
	Bus	Contains several wires. Usually for data / address.
	Bus
	Bus
	Optocoupler / Opto-isolator	Optocoupler isolates connection to other board
	Loudspeaker	Converts electrical signal to sound waves
	Microphone	Converts sound waves to electrical signal
	Operational Amplifier	Amplify input signal
	Schmitt Trigger	Operates with hysteresis to reduce noise.
	Analog-to-digital converter (ADC)	Converts analog signal to digital numbers
	Digital-to-Analog converter (DAC)	Converts digital numbers to analog signal
	Crystal Oscillator	Used to generate precise frequency clock signal
Antenna Symbols
	Antenna / aerial	Transmits & receives radio waves
	Antenna / aerial
	Dipole Antenna	Two wires simple antenna
Logic Gates Symbols
	NOT Gate (Inverter)	Outputs 1 when input is 0
	AND Gate	Outputs 1 when both inputs are 1.
	NAND Gate	Outputs 0 when both inputs are 1. (NOT + AND)
	OR Gate	Outputs 1 when any input is 1.
	NOR Gate	Outputs 0 when any input is 1. (NOT + OR)
	XOR Gate	Outputs 1 when inputs are different. (Exclusive OR)
	D Flip-Flop	Stores one bit of data
	Multiplexer / Mux 2 to 1	Connects the output to selected input line.
	Multiplexer / Mux 4 to 1
	Demultiplexer / Demux 1 to 4	Connects selected output to the input line.

Hope you must have gotten what is a circuit diagram and its prerequisites to understand.

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After being aware of component name and symbol; one should also check its function in real world. You can check functionality from Google. Next most important prerequisite is the selection of efficient software for design and construction of a circuit diagram.

We will elaborate the top 10 free software for circuit diagram / schematic here.

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