An electrical circuit is a complete loop that allows electric current to flow from the power source to components and back to the source. Even the most complex electronics consist of combinations of simple circuits performing specific functions.
This article provides a step-by-step walkthrough on how to make basic working circuits using common components and supplies. It covers fundamental circuit theory, schematic symbols, breadboard and PCB construction, component selection, safety measures and troubleshooting basics.
Learning how to assemble simple circuits forms the foundation for more advanced electronics projects and helps demystify how devices around us work.
Circuit Theory Basics
To understand how to make a functioning circuit, it helps to first cover some basic electrical principles:
What is Electric Current?
Electric current is the orderly flow of charged electrons through a conductive path. It is measured in Amperes.
Ohm’s law relates voltage (V), current (I) and resistance (R). It states:
V = I x R
where V is in Volts, I is in Amperes and R is in Ohms.
Kirchoff’s Current Law (KCL) – Total current entering any junction must equal total current leaving it.
Kirchoff’s Voltage Law (KVL) – Sum of all voltages in a closed loop must equal zero.
Power (P) = Voltage (V) x Current (I)
Series and Parallel
Components connected end to end are in Series. Current is same through all.
Components side by side are in Parallel. Voltage is same across all.
These fundamental principles govern current, voltage and power relationships in electrical circuits.
Circuits are represented using standard symbols before constructing them. Some common symbols include:
|Electronic Component||Schematic Symbol|
These symbols are used to create circuit diagrams showing connections before physically constructing the circuit.
Tools and Components
Some essential tools and components needed for assembling simple circuits are:
- Multimeter – Measures voltage, current, resistance
- Needle nose pliers – For bending and cutting component leads
- Wire cutters – Cutting wires to size
- Wire strippers – Removing insulation from ends of wires
- Soldering iron and solder – For permanent circuits
- Safety glasses – Protect eyes from debris
- Resistors – Limit flow of current
- Capacitors – Store electric charge
- Transistors – Semiconductors that amplify or switch
- Diodes – Allow current flow in one direction
- LEDs – Light emitting diodes
- Integrated circuits – Prebuilt circuits for complex functions
- Battery – Provides electrical energy
- Wires – Transport current between components
Having these supplies on hand will enable building a wide range of simple demonstrative circuits.
Breadboards provide a convenient way to prototype circuits without soldering. The contact holes are connected in rows underneath to distribute power and signals.
- Power bus strips on sides supply positive and negative terminals.
- Components plug in spanning center gap.
- Jumper wires make connections.
Breadboards allow creating temporary circuits and modifying them easily.
Selecting proper components involves checking:
- Resistor values – Measured in ohms (Ω). Common values are 220Ω, 1kΩ, 10kΩ.
- Capacitor values – Rated in farads (F). Common are 0.1μF, 1μF.
- Power ratings – Resistors and capacitors should be rated for at least 1/4 watt.
- Voltage ratings – Must exceed circuit voltage. Electrolytic capacitors are polarity sensitive.
- Inductors – Measured in henries (H). Values like 1mH, 10mH used.
- Transistors – Small signal or power types, NPN or PNP, voltage and power rating.
- Integrated Circuits – Choose IC complexity needed. Check supply voltage and logic levels.
Matching electrical characteristics of components to the circuit requirements ensures proper functioning.
- Use insulated hookup wire solid core wire for breadboards, stranded for soldering.
- Cut wires to required lengths using wire cutters.
- Strip off about 1⁄4 inch of insulation from ends using strippers.
- Make firm insertions into breadboard holes or solder joints.
- Use wire colors toaid in following circuit layout.
- Avoid loose connections which can cause erratic operation.
Using quality connections helps circuits perform reliably.
Sample Circuit 1 – LED
This circuit lights an LED using battery power.
- 5mm LED
- 470Ω resistor
- 9V battery
- Jumper wires
- Insert 470Ω resistor on breadboard spanning center gap.
- Place LED across gap with longer lead on the same side as resistor.
- Connect 9V battery positive to resistor end.
- Connect battery negative to LED other end.
- LED illuminates.
This demonstrates using a resistor to limit current through an LED.
Sample Circuit 2 – Transistor
This circuit uses a transistor to switch on an LED.
- BC548 NPN transistor
- 10kΩ resistor
- 470Ω resistor
- Red LED
- 9V battery
- Connect switch, 10kΩ resistor, base of transistor in series.
- Emitter connects to negative side of LED.
- Positive supply to collector via 470Ω resistor.
- Close switch, transistor conducts switching on LED.
- Open switch, transistor switches off turning LED off.
This demonstrates using a transistor as an electrically controlled switch.
Sample Circuit 3 – 555 Timer
This circuit uses a 555 timer IC to flash an LED.
- NE555 Timer IC
- 10kΩ resistor
- 1kΩ resistor
- 10μF capacitor
- Red LED
- 9V battery
- Insert NE555 timer on breadboard with pins spanning gap.
- Connect pin 8 to positive voltage.
- Connect pin 1 to negative via 10kΩ resistor.
- Connect capacitor between pins 6 and 7.
- Connect pin 3 to positive via 1kΩ and LED.
- On power up, LED starts flashing periodically.
Demonstrates using a 555 timer in astable mode to generate flashing output.
Moving to PCB
For permanent circuits:
- Design schematic and PCB layout.
- Order fabricated bare PCB.
- Solder components onto board.
- Provides rugged encapsulated circuit.
Use soldering iron, solder, and flux for assembling PCB.
Electrical Safety Tips
- Use batteries or low voltage sources to limit shock hazard.
- Avoid touching bare conductors when powered.
- Do not touch components connected directly to wall sockets.
- Unplug supply when adjusting partially assembled circuits.
- Double check polarities before connecting batteries.
- Wear safety glasses and be mindful of hot solder/iron.
Following basic precautions is important when working on circuits.
Common circuit issues include:
|Circuit dead,no activity||Power not reaching circuit, loose connection, blown fuse|
|Short circuit, high current flow||Component leads touching, incorrect resistor value|
|Component getting hot||Excess current flow, undersized resistor|
|Component not working||Wrong placement, incorrectly wired|
|Erratic circuit behavior||Cold solder joint, wire intermittance|
|Weak signal||Depleted battery, low supply voltage|
|LED not lighting||Wrong polarity, inadequate current limiting|
|IC not functioning||Incorrect pin connections|
Methodically checking connections, voltages and component placement helps identify issues.
In summary, assembling simple functioning circuits involves:
- Understanding fundamental circuit theory concepts
- Selecting appropriate components
- Planning layouts using schematic symbols
- Using solderless breadboards for initial prototyping
- Making firm reliable connections
- Testing circuits systematically and troubleshooting issues
- Iterating designs using PCBs for permanent circuits
Learning these basics helps demystify circuits for enthusiasts. One can leverage online circuit simulators and community forums for more complex circuits. Building circuits helps develop electronics skills in a hands-on manner.
Frequently Asked Questions
Q1. What is the simplest electrical circuit?
The simplest complete circuit consists of a battery with positive and negative terminals connected by a single conductive wire looped between them. This allows a flow of continuously circulating current.
Q2. What components are best to learn basic circuits?
Recommended entry-level components like resistors, capacitors, diodes, LEDs, transistors, ICs like 555 timer and 741 op-amp allow assembling a wide variety of basic circuits for learning fundamentals.
Q3. Is any special equipment needed for building circuits?
A basic toolkit consisting of a solderless breadboard, jumper wires, needle nose pliers, cutters, strippers, multimeter and a low voltage power source is sufficient to get started. Advanced tools can be added later as needed.
Q4. What safety gear should be used when prototyping circuits?
Safety glasses should always be worn to prevent eye injuries from debris. Electrical gloves, enclosed footwear, and protective clothing should be used if working with high voltages. Work in a clutter-free, dry area away from flammables.
Q5. What resources are available for learning more about circuits?
Online circuit simulators, builder communities like Instructables, textbook guides like “Art of Electronics”, YouTube channels like EEVBlog, Great Scott and Make Electronics, online course platforms like Coursera, and hands-on training institutes like Makerspaces provide deeper learning opportunities about electronics circuits.