Small practical electronics projects covering analog circuits, digital logic, Arduino, sensors, and mixed-signal experiments.
Build lighting for a fish tank that reacts to ambient light on its own. Three LEDs are involved: the white ones should glow more strongly as daylight gets brighter, while the blue ones take over once it gets dark. Sensing is done with a small solar cell, which reaches about 15 V under full midday sun. The circuit should stay simple and use only basic components.
A lamp manufacturer needs a quick go/no-go test for its 12 V lamps: anything drawing more than 1 A fails. Come up with the lowest-cost circuit that turns on a red LED above that threshold and a green LED below it — essentially a one-point current comparison with a visual output.
Add a state-of-charge indicator to a device running from a 12 V battery. The circuit draws its own supply from that same battery and compares the terminal voltage against a 10 V threshold: green above it, red below it.
Design temperature-triggered switching for an engine cooling fan. Once the measured temperature climbs past the set point, the fan should turn on by itself, with no manual input.
Revisit the previous fan circuit and add hold-over behaviour. Rather than cutting out the instant the temperature falls back, the fan should keep running for a short while afterwards before shutting down.
Give a homeowner keyless entry to a room. Entry is by typing a stored passcode on a keypad, so nothing has to be carried around; a correct entry releases the lock.
For a toy manufacturer, work out a way to reverse a DC motor from a joystick — pushing one way spins the motor forward, pushing the other way spins it backward.
Let a homeowner know from indoors whether anything has arrived in the mailbox. Something dropped into the box should be detected, and an LED should then stay lit rather than flashing briefly.
Create a parking aid that signals distance by tone instead of a display. A speaker sounds a pitch that climbs higher as the vehicle closes in on a wall. An LDR is one option for sensing the distance, though any other suitable sensor is acceptable.
Extend the mailbox project with a more expressive output. Instead of a single LED, drive a 7-segment display that spells out POST one character at a time in sequence whenever mail is detected.
A manufacturer needs a way to alternate between two lamp settings of different output — one equivalent to three LEDs, the other to five. A single ordinary switch is the only control the user gets, so the circuit itself has to handle the toggling logic. Build it around a 555 timer.
A plant supervisor needs the four operations his machine performs to fire in a fixed order rather than at random. Build a circuit that issues a trigger signal to each of the four stages one after another, cycling through them in sequence. Use 555 timers together with a few basic components.
Starting from a clock source that ticks once per second, use a CD4017 decade counter to drive two banks of LEDs so that they flash back and forth — one bank on while the other is off, swapping on every pulse.
Build a starting-signal circuit for a race. It counts down through three, two, one, and then gives the "go" indication — a drag-strip style light tree, where each stage holds for a fixed interval before advancing to the next.
Note: the output stage is left open — three sequential LEDs plus a final one, a 7-segment showing the digits, or a countdown with an audible tone at the start. A 555 clock feeding a CD4017 would cover it.
A client wants a saleable consumer product: a lamp toggled by hand claps. Each clap flips the lamp to the opposite state — on becomes off, off becomes on. A microphone-based sound detector supplies the trigger, and a CD4017 handles the toggling.
Note: the CD4017 is a ten-stage counter being used for a two-state job, so reset it after the second step to make it divide by two. The harder part in practice is the front end — the sound detector needs enough conditioning to fire once per clap rather than several times on one sharp transient.
An extension of the clap-lamp idea, now with multiple brightness levels instead of a simple toggle. Each clap advances the LED through a four-state cycle: off, full brightness, medium, dim, then back to off. As before, a sound sensor provides the trigger and a CD4017 tracks which state you're in — but here three of its outputs each need to produce a different current through the LED rather than just switching it.
A company wants the cheapest possible control board for an electric household water heater. Design a simple thermostat built around a Schmitt trigger, adding a relay and whatever basic components you need. The switching thresholds are deliberately separated: the heater cuts out once the water passes 60°C and switches back on when it falls to around 40°C.
Note: that 20°C gap is the point of the exercise — the hysteresis is what stops the relay from chattering around a single set point, and the Schmitt trigger is where you set it.
Put the oscillator and step-up converter material to practical use. Design a handheld torch powered by a single 3.7 V lithium cell that drives a string of six white LEDs wired in series.
Note: the series arrangement is what forces the design — six white LEDs stack up to roughly 18–20 V of forward drop, well above the cell, so a boost stage is unavoidable. Current regulation matters more than voltage regulation, since the LEDs share one current path.