Electronics and robotics
Electronics and robotics projects for class 9 and 10: 72 ideas.
Each project below opens to its own page with what it shows, the science behind it, the materials, safety, step-by-step instructions, what you should see and viva questions. Many can be made from things at home; where a kit helps, the page links one.
Other subjects for class 9 and 10: Physics, Chemistry, Biology, Maths, Earth and space, Environment, Computing and coding.
Automatic street light with an LDR
A light dependent resistor (LDR) has a high resistance in the dark and a low resistance in light. A transistor uses that change to switch the LED on when it gets dark.
Water level indicator
Tap water conducts a little electricity because of the salts dissolved in it. As the water rises it touches wires at different heights, and transistors light an LED or sound a buzzer for each level.
Smart dustbin with Arduino
An ultrasonic sensor sends out a pulse of sound and times its echo to measure distance. When a hand comes close, the Arduino tells a servo motor to lift the lid.
Obstacle-avoiding robot
The robot measures the distance ahead with an ultrasonic sensor. When something is too close, the program stops, turns and looks for a clear path, driving the motors through a motor driver.
Line follower robot
IR sensors shine infrared light at the floor: white reflects it and black absorbs it. The controller reads which sensor sees the line and steers the motors to stay on it.
Automatic plant watering system
A soil moisture sensor gives a reading that changes with the water in the soil. When the soil is dry, the Arduino switches on a small pump until it is moist again.
Pocket dark detector that beeps when you cover the LDR
A light dependent resistor has a low resistance in bright light and a very high resistance in the dark. In a voltage divider with a fixed resistor, this change swings the base voltage of a transistor, which switches a buzzer on when it gets dark.
Bucket overflow alarm that beeps when water touches two wires
Tap water conducts a small current because of dissolved salts. Two BC547 transistors joined as a Darlington pair multiply that tiny current enough to drive a buzzer, so the alarm sounds the moment water bridges the probe wires.
Rain alarm with an interleaved foil strip sensor on a card
Raindrops bridge the gap between two sets of foil strips that are close but not touching. The water lets a tiny current flow, which a Darlington pair of BC547 transistors amplifies to sound a buzzer, warning you to bring the washing in.
Two-station Morse telegraph line across a room with LEDs
Two keys and two indicator LEDs on one long wire pair let either station send to the other. It shows that a signal is really a current switched on and off, and that one shared return wire is enough for a two-way line.
Energy transfer: one toy motor spins another that lights an LED
A DC motor is also a generator. When a second motor is turned by the first, its coil spins inside its magnets and produces a voltage that lights an LED, showing that electrical and mechanical energy can be converted in both directions.
Salt water conductivity tester with a transistor and an LED
Water conducts electricity only through dissolved ions. Two probes in a liquid feed a tiny current into a transistor, which amplifies it to light an LED. Distilled water gives nothing, tap water a faint glow and salt water a bright one.
Pocket continuity tester with a buzzer and an LED in a tic-tac box
A continuity tester tells you whether a path conducts: touch its two probes to the ends of a wire, a fuse or a switch and it beeps if current can flow. It is the first tool for finding broken wires and checking which materials conduct.
Cardboard conveyor belt driven by a toy motor and rubber band
A motor turns a small pulley, a rubber band carries that rotation to a larger roller, and a loop of cloth belt stretched between two rollers moves objects along. It shows belt drives, friction grip and speed reduction through pulley sizes.
Motorised cardboard crane that lifts a load with a thread spool and reversing switch
A motor winding thread onto a spool converts rotation into lifting. A DPDT slide switch swaps the battery polarity so the same motor raises and lowers the hook, which is how real crane winches are controlled.
Electric bell model with a nail electromagnet and a hacksaw blade clapper
An electromagnet pulls a springy steel strip towards it, which breaks its own contact, loses the magnetism and springs back to close the contact again. The strip vibrates to and fro, striking a tin lid to ring like a doorbell.
555 timer blinking an LED once a second on a breadboard
A 555 timer in astable mode charges and discharges a capacitor through two resistors, producing a steady stream of pulses. With 1 kΩ, 470 kΩ and 1 µF the output switches about 1.5 times a second, blinking an LED without any switch being pressed.
Finger touch sensor with two BC547 transistors that lights an LED
Dry skin has a resistance of hundreds of kilohms, far too high to light an LED directly. Two transistors in a Darlington pair multiply the microampere current through a fingertip by about 40,000, so a light touch across two pads switches the LED on.
555 tone generator with a knob that changes the pitch of a piezo disc
Running a 555 astable fast enough produces audio frequencies. A potentiometer changes the timing resistance, so turning the knob slides the pitch up and down, demonstrating the link between frequency and pitch.
Magnetic door alarm with a reed switch that sounds when the door opens
A reed switch closes when a magnet is near and opens when it moves away. With the magnet on the door and the switch on the frame, opening the door removes the magnet, and a transistor circuit turns the buzzer on, the same way shop door sensors work.
Bicycle wheel revolution flasher with a spoke magnet and a reed switch
A magnet on a spoke closes a reed switch on the fork once every turn, flashing an LED. Counting flashes in a known time and knowing the wheel circumference gives the bicycle speed, the same method a bike speedometer uses.
Thermistor hot water warning that beeps when a cup gets too hot
An NTC thermistor loses resistance as it warms. In a voltage divider with a potentiometer, warming raises the transistor base voltage until it switches a buzzer on, giving an adjustable temperature alarm like the one in a geyser or a kettle.
Cold night warning LED for seedlings using an NTC thermistor
With the thermistor placed on the ground side of a voltage divider, cooling raises its resistance and the base voltage, lighting an LED when the air drops below a set temperature. It shows how the same sensor can trigger on cold instead of heat just by swapping its position.
Relay latching alarm that stays on after one press until reset
A relay module can hold itself on: once its coil is energised, its own contact keeps feeding the coil even after the trigger button is released. This latch is how real alarm panels remember that a sensor tripped, until someone presses reset.
Night fan: an LDR and relay module that start a motor when it gets dark
A small sensor signal can control a bigger load through a relay. The LDR and transistor sense darkness, the relay module switches a separate motor circuit, and the two circuits never share current, which is how electronics controls heavy machinery.
Solar powered spinner: a small solar cell drives a toy motor top
A solar cell turns light directly into electrical energy. Connected to a toy motor with a paper disc, it spins in sunlight, slows in shade and stops indoors, showing how output depends on the amount and angle of light.
How the angle of a solar cell changes its voltage and LED brightness
The electrical output of a solar cell falls as the light strikes it at a shallower angle, because the same beam is spread over a bigger area. Measuring voltage and current at known tilt angles shows why rooftop panels in India are tilted roughly at the latitude angle.
PIR corridor light that stays on for a set time after movement
A passive infrared (PIR) sensor detects the heat of a moving person. An Arduino switches a 12 V LED strip on through a relay and keeps it on for a timer period that restarts with every new movement, so the light never cuts out while someone is still walking.
Room comfort meter with DHT11 and an OLED display
A DHT11 measures temperature and relative humidity, an Arduino calculates a heat index, and a small OLED screen shows the readings with a comfort message. The project shows how a digital sensor sends numbers over one wire.
Flame sensor store room alarm with a small sprinkler pump
An infrared flame sensor module detects the flicker and wavelength of a flame from a metre away. The Arduino sounds an alarm and runs a 5 V submersible pump through a relay so a tiny sprinkler sprays water on the model store room.
Automatic curtain that opens at dawn using an LDR and a DC motor
An LDR measures daylight, the Arduino decides open or closed, and an L298N driver runs a geared DC motor in either direction to pull a string curtain across a model window. Two limit switches stop the motor at each end.
Rain sensor that closes a model window with a servo when drops fall
A rain sensor board has interleaved copper tracks whose resistance drops when water bridges them. The Arduino reads that change and swings a servo to shut a hinged cardboard window, then reopens it when the board dries.
Tipping bucket rain gauge with a reed switch counted by Arduino
Rain collected by a funnel fills one side of a tiny see-saw bucket; when it tips, a magnet passes a reed switch and the Arduino counts one tip. Knowing the volume per tip and the funnel area gives rainfall in millimetres on an LCD.
Field bird scarer that flaps and beeps when a PIR detects movement
A PIR sensor detects a bird or animal entering a model field; the Arduino then flaps a shiny ribbon with a servo and plays random beeps for a few seconds. Random timing stops birds getting used to it, a real problem with fixed scarecrows.
Grain store humidity alarm with an ESP8266 that warns the phone
A DHT11 inside a model grain bin watches humidity; stored grain spoils and grows mould when air humidity stays high. The NodeMCU shows the reading on a phone page, sounds a buzzer and sends an alert when humidity stays above a limit for a set time.
Classroom noise meter with a sound sensor, LED bar and OLED readout
A microphone sound sensor module gives a voltage that swings with sound pressure. The Arduino measures the swing over short windows, shows it on an LED bar and an OLED, and flashes a warning when the class is too loud for too long.
Alternate LED flasher with two BC547 transistors and two capacitors
Two transistors, each switching the other through a capacitor, make an astable multivibrator: a circuit with no stable state that swaps over by itself. The two LEDs flash alternately about once a second.
LED strings on a 9 V battery: working out resistors for series and parallel
Three red LEDs in series share one resistor and draw one LED worth of current, while three in parallel each need their own resistor and draw three times as much. Working out the resistor with R = (supply minus LED voltages) divided by current shows why.
Knob dimmer for an LED using a 10 kΩ potentiometer on a 9 V battery
A potentiometer wired as a variable resistor changes how much current an LED gets, so turning the knob dims or brightens the light. Less resistance gives more current and more light.
Weak cell finder: loaded and unloaded voltage of old and new AA cells
A cell that reads 1.4 V with nothing connected can still be nearly flat, because its internal resistance has grown. A voltage reading while it lights a small bulb shows the true condition.
Three-LED water level indicator for a bottle using three BC547 transistors
Water with a little salt conducts a tiny current. Each probe that touches the water passes enough base current to switch a BC547 on, so one LED lights for each level reached.
Polarity-proof LED lamp: a four-diode bridge that works either way round
A diode lets current through in one direction only. Four diodes arranged as a bridge always pass the current the same way through the LED, so the lamp lights even if the battery is connected backwards.
Push button LED that fades out slowly, powered by a charged capacitor
A capacitor stores charge like a tiny rechargeable tank. A quick press of a button fills it, and when the button is released the capacitor keeps the LED glowing for several seconds as it empties.
Measuring the current gain of a BC547 with a 1 MΩ and a 1 kΩ resistor
A transistor turns a very small base current into a much larger collector current. The ratio Ic / Ib, called the current gain, can be found with a multimeter and two resistors.
Hot water alarm that buzzes when an NTC thermistor reaches about 45 degrees
An NTC thermistor is a resistor whose resistance falls as it gets hotter. In a voltage divider, this change swings a transistor base voltage and switches a buzzer on at a chosen temperature.
Light-chasing buggy with two LDR eyes steering two toy motors
Each light dependent resistor switches the motor on the opposite side, so the buggy turns towards the brighter side and drives at a torch. This is a simple analogue form of phototaxis used in robots.
Knock sensor: a piezo disc and a BC547 that flash an LED when you tap the desk
A piezoelectric disc makes a small voltage when it is squeezed or struck. A transistor amplifies this short pulse so it lights an LED for a moment.
Secret code box: four toggle switches in series that light an LED in one setting
Switches in series work like the word AND: the loop is complete only if every switch is in its correct position. With four two-way toggles there are 16 settings and only one lights the LED.
Toy motor dynamo run by a bicycle tyre with two opposite LEDs
A DC motor works backwards as a generator. When its shaft is turned by a spinning tyre it makes a voltage, and reversing the spin reverses the voltage, which lights the other LED of an opposite pair.
Voltage divider board: measured against calculated voltages with a 10 kΩ load
Two resistors in series share a voltage in proportion to their sizes. A load connected to the output pulls the voltage down, which is why dividers are not power supplies.
Two-tone siren built from two 555 timers and a small speaker
One 555 timer makes a slow beat of about one per second, and it wobbles the pitch of a second 555 that produces an audible tone. Together they give a rising and falling siren.
Delay light: two BC547 transistors and a 100 µF capacitor that switch on after 20 seconds
A capacitor charges slowly through a very large resistor. Only when its voltage reaches about 1.4 V does a pair of transistors, the Darlington pair, switch the LED on, giving a timed delay.
Eight-key toy organ with a 555 timer and a trimmer for each note
The pitch of a 555 astable depends on its timing resistor. Eight keys, each connecting a different resistor, give eight notes of a musical scale.
Adjustable metronome with a 555 timer, a knob, an LED and a click
A very slow 555 astable circuit beats like a clock. A 100 kΩ potentiometer sets the speed from about 35 to 160 beats per minute, which is useful for music practice.
How fast a toy motor spins with one, two, three and four AA cells
The speed of a DC motor rises almost in proportion to the voltage across it. More cells in series give more speed and also a larger current.
Plant pot dry soil alert with two steel nails, a BC547 and an LED
Damp soil conducts electricity far better than dry soil. A transistor circuit lights a red LED when the soil resistance between two nails rises, which tells you the plant needs water.
One LED used as a light sensor that switches a second LED through a BC547
An LED is a diode that makes light when current passes, but in strong light it also makes a small voltage itself. A transistor can use this voltage to switch another LED on, so one LED acts as a light sensor.
Capacitor charging curve plotted from a multimeter and a stopwatch
A capacitor charges quickly at first and then more slowly, following an exponential curve. The time constant RC is the time to reach about 63 percent of the supply voltage.
Propeller thrust test: how blade angle and blade number change the push
A propeller pushes air backwards and is pushed forwards in return. The size of the push depends on how many blades there are and how they are angled to the air.
Car parking sensor with an Arduino whose beeps speed up as the wall nears
An ultrasonic sensor measures distance from the time an echo takes to return. The Arduino turns this distance into LED steps and a beeping speed, like the sensor in a car bumper.
Digital room thermometer with an LM35 and LCD showing the day’s minimum and maximum
The LM35 gives 10 millivolts for every degree Celsius. The Arduino reads this voltage with its analog input, converts it to degrees and shows the present, lowest and highest readings on a screen.
Digital lap stopwatch with an Arduino, three buttons and an LCD
The millis() timer counts milliseconds since the board started. Storing the start time and subtracting it from the present value gives elapsed time, which can be shown to a hundredth of a second.
Two-road traffic junction with an Arduino and a pedestrian crossing button
A traffic controller is a state machine: the lights follow a fixed sequence, but a pedestrian button can ask for a change. It shows how timing and input are combined in a program.
Reaction time tester with random delay and false start detection (Arduino)
The time between a light and your button press is your reaction time, usually around 0.2 to 0.3 seconds. A microcontroller timer measures it to a thousandth of a second, so you can compare people and conditions.
Simon memory game with four coloured LEDs, buttons and a buzzer
The Arduino stores a growing random sequence in an array, plays it with lights and tones, and checks the player repeats it. It teaches arrays, loops and random numbers in a game.
Four-servo robot arm that copies the angles of four knobs
Each joint of the arm is a servo whose angle is set by a PWM signal. Reading four potentiometers and mapping each to 0 to 180 degrees lets you pose the arm by hand-turned knobs and pick up light objects.
Hand-wave theremin: an ultrasonic sensor that plays higher notes as your hand nears
The Arduino turns the distance of your hand into the frequency of a tone, so you can play music in the air. It shows how a sensor reading can be mapped to a sound.
Touch-free soap dispenser with an ultrasonic sensor, relay and small pump
When a hand comes within about 10 cm, the sensor detects it and the Arduino runs a small pump for a fraction of a second. It shows how sensors, relays and timers are combined in a hygiene device.
Temperature-controlled 5 V fan with PWM speed steps and a logic-level MOSFET
Pulse width modulation switches a fan on and off thousands of times a second; the fraction of time it is on sets the average power and speed. The Arduino raises the duty cycle as the temperature climbs, as a computer cooling fan does.
Double-clap switch for a 5 V USB lamp with a sound sensor and relay module
A sound sensor turns the loud burst of a clap into a signal. The Arduino counts claps within a time window and toggles a relay, which switches a small lamp on and off.
Old TV remote that switches three LEDs and a servo through an IR receiver
A remote control flashes an invisible infrared LED in a coded pattern, and a receiver module decodes it into a number. The Arduino can read that number and act on it, so any old remote becomes a controller for your projects.
Coin-cell LED night lamp with an ice-cream stick switch
A complete circuit of a cell, an LED and a switch lights the lamp. It shows that current flows only in a closed loop and that an LED works in one direction only.