projects

Build something real.

Every project explains why the circuit works — actual numbers, not magic — and ends with a challenge that has more than one right answer.

L1 Light

Your first circuits — make light happen.

First Light Build a real flashlight circuit and learn why every circuit is a loop. 15 min · ●○○○○ Morse Code Messenger A push button, an LED, and a secret code — send real messages with light. 20 min · ●○○○○ Twin Reds Two red LEDs on one loop — same current, half the leftover push, and a lesson in how voltages stack when parts sit end to end. 15 min · ●○○○○ Two Greens Twin Reds with green LEDs — bigger voltage bites, less leftover for the resistor, and a great lesson in how far a 4.5 V battery can actually push. 15 min · ●○○○○ Night Pin One 10 kΩ, one red LED, one slide — the simplest dimmer. A single big resistor runs the LED at 0.27 mA: invisible in daylight, perfect for a dark room. 10 min · ●○○○○ Tabletop Traffic Light Three LEDs on three parallel lanes, all lit by one switch — build a tabletop traffic light and discover parallel circuits. 25 min · ●●○○○ Bike Torch One yellow LED, two switches: a slide for a battery-friendly low beam, a push button for a bright flash, both lanes feeding the same lamp in parallel. 15 min · ●●○○○ Signal Pair Two push buttons, two LEDs, one battery — no sharing. Each button lights its own lamp with its own current, independent of the other. 15 min · ●●○○○ Dim Candle A 1 kΩ and a 10 kΩ in series throttle a red LED to a candle glow. Flip the bypass slide — the 10 kΩ gets shorted and the LED pops to normal brightness. 15 min · ●●○○○ Three Sisters Three red LEDs side by side from one battery — each with its own 220 Ω — proving parallel lanes do their own Ohm's law and the battery adds the bill. 15 min · ●●○○○ One for All Three LEDs on ONE shared 220 Ω — the shortcut that fails. Red and yellow dim-split the current; green sits dark. Lesson: each LED needs its own resistor. 15 min · ●●○○○ Step Up Three 1 kΩ lanes in parallel into one red LED, each with its own slide switch. One slide = candle, two = glow, three = full lamp. The lanes stack. 15 min · ●●○○○ Longer Loop Three 1 kΩ speed bumps stacked end-to-end on one lane feed a single red LED. Resistors in series ADD up — the LED is throttled to a near-dark 0.87 mA. 15 min · ●●○○○ Bright and Dim Two red LEDs on one battery — one through 220 Ω (bright), one through 1 kΩ (candle). Same LEDs, two currents. The resistor sets each lane's brightness. 15 min · ●●○○○ Rainbow Loop Red, yellow and green LEDs on three parallel 220 Ω lanes under one slide. One flip lights all three, each lane running its own Ohm's law. 15 min · ●●○○○ Reserve Beacon A 10 kΩ in series with the LED keeps a dim always-on pilot glow. Flip the bypass slide — it shorts the 10 kΩ, and the pilot pops to full First-Light brightness. 15 min · ●●○○○ Short Cut First Light with a slide switch wired straight across the LED. Flip the slide and the LED goes dark even though the loop stays complete. 15 min · ●●○○○ The Vault Two buttons, one loop — the LED only lights when BOTH are pressed at the same time. 15 min · ●●○○○ Do Not Disturb Sign A green "chill" LED plus a switched red "leave me alone" LED — two lanes on one battery, and a switch that only touches one of them. 20 min · ●●○○○ Handhold Chain Three switches in a line — the LED only lights when all three are closed at once. AND, one step past The Vault. 15 min · ●●○○○ Two-Door Signal Two slide switches in parallel, one shared LED — either switch alone lights the lamp. The OR gate, at Level 1. 15 min · ●●○○○ Signal Light A slide switch and a push button in parallel — the slide is the steady beacon, the button is the extra flash. Either lights the lamp. 15 min · ●●○○○ Escape Hatch The Vault with a big red emergency button wired around both locks — turn BOTH keys, or hit the button, and the light comes on. 20 min · ●●○○○ The Brightness Lab Run a real experiment: predict, measure with your eyes, and prove Ohm's law. 30 min · ●●●○○

L2 Sound

Add noise. Doorbells, alarms, annoying siblings.

Door Buzzer Your first sound circuit — a real doorbell for your bedroom door. 20 min · ●○○○○ Pocket Beeper Level 2's answer to First Light: battery, push button, buzzer. Three parts, one loop, one loud beep — no resistor and no LED to explain. 10 min · ●○○○○ Dial-a-Brightness Twist a knob and watch the LED fade up and down — your first "how much" input. 20 min · ●●○○○ Dial-a-Buzz Dial-a-Brightness for sound — one knob rides the buzzer between full alarm and library silence, with no button in the way. 15 min · ●●○○○ Continuity Tester Your first real tool — two probe wires that beep and light up whenever the tips touch anything that conducts. 20 min · ●●○○○ Panic Doorbell Two buttons wired so either one fires the same buzzer and light — your first OR gate. 20 min · ●●○○○ Whisper Alarm A doorbell with a volume knob — the pot lives in the buzzer lane, so twisting it changes the beep without touching the light. 25 min · ●●○○○ Two-Tone Doorbell Two call buttons, one doorbell: LOUD rings the buzzer and lights the porch LED; QUIET starves the buzzer and shows why it can't just be dimmed. 25 min · ●●○○○ Arm & Ring A doorbell that ignores you unless a hidden slide switch is armed first — series-AND with sound, plus an 'armed' LED that shows the state. 20 min · ●●○○○ Twin Bells One doorbell button rings two buzzers in parallel — one in your room, one in the kitchen — with a slide switch that mutes just the bedroom bell at night. 20 min · ●●○○○ Two-Hand Bell Two push buttons in series feeding a buzzer and an LED — both hands must stay pressed for the alarm to sound. 20 min · ●●○○○ Silent Alarm Three panic buttons wired in parallel, all inside an armed lane — any one of them fires the buzzer, and a small LED tells you the alarm is watching. 25 min · ●●○○○ Quiz Buzzer Two teams, two big buttons: yours lights your LED and rings your buzzer, theirs does the same on their side. Two independent doorbells sharing one battery. 20 min · ●●○○○ Loud/Polite Doorbell One doorbell button, one buzzer, and a slide switch that shorts across a 1 kΩ resistor — flip it to swap between a startle-loud beep and a scratchy whisper. 20 min · ●●○○○ Duet Doorbell One button, two buzzers in parallel — one wired direct at full 30 mA, one starved through a 220 Ω to about 12 mA — voicing together at two different loudnesses. 20 min · ●●○○○ Vault Chime Three slide switches in a line, a buzzer and a red LED hanging off the end — the chime only sings and glows when every single switch is closed. 20 min · ●●○○○ Hidden Mute A doorbell with a secret slide switch tucked inside just the buzzer lane: flip it and the ring button still lights the LED, but the sound stays off. 15 min · ●●○○○ Power Pilot A green pilot LED that glows the whole time the battery is plugged in, next to a red alarm LED and buzzer that only fire when the button is pressed. 15 min · ●●○○○ Shared Knob One pot sits above the merge of two parallel LED lanes (red + yellow). Twist it and BOTH LEDs fade together — the knob throttles the shared rail. 15 min · ●●○○○

L3 Sense

Circuits that react to the world around them.

Automatic Night Light A light that switches itself on when the room gets dark — no hands, no code. 35 min · ●●●○○ Sunrise Alarm The night light — flipped. Swap two parts and the LED wakes up with the sun instead. 25 min · ●●●○○ Cookie Jar Alarm The Sunrise Alarm's brain wired to a buzzer instead of a lamp — quiet in the dark jar, screaming when the lid comes off. 25 min · ●●●○○ Trip Wire Alarm A thin wire across a doorway holds the alarm silent. Break the wire and the buzzer screams — until you connect it back. 25 min · ●●●○○ Warm Hand Alarm Cup your hand over the sensor and the LED lights up — a thermometer that turns into a switch. 30 min · ●●●○○ Reading Light The Automatic Night Light with a knob on top — turn it to dial in how dark the room has to get before the lamp fires. Your first tunable threshold. 30 min · ●●●○○ Vacation Nightlight The Automatic Night Light with a manual override — flip the slide switch off and the lamp stays dark even in a pitch-black room. 25 min · ●●●○○ Study Lamp The Automatic Night Light with a force-on override — flip the slide switch and the lamp stays lit even in daylight, ignoring the sensor. 25 min · ●●●○○ Curfew Beeper The Automatic Night Light's brain with a buzzer where the LED used to sit — beeps the moment the room goes dark, so you never miss sunset. 30 min · ●●●○○ Fever Beeper The Warm Hand Alarm's brain wired to a buzzer instead of a lamp — silent in a normal room, beeping the second a warm palm covers the sensor. 25 min · ●●●○○ Dusk Chorus The Curfew Beeper with a red LED wired in parallel with the buzzer — one dusk sensor drives a chime and a lamp at the same time. 30 min · ●●●○○ Warm Hand Chorus Fever Beeper with a red LED added in parallel with the buzzer — one warm-hand sensor drives a chime and a lamp at the same time. 30 min · ●●●○○ Dawn Chorus Cookie Jar Alarm with a red LED added in parallel with the buzzer — one light sensor drives a chime and a lamp the moment the sun hits. 30 min · ●●●○○ Trip-Wire Chorus Trip Wire Alarm with a red LED added in parallel with the buzzer — one thin wire holds the whole chorus silent; snap it and both mouths fire. 30 min · ●●●○○ Night Doorbell A doorbell that only works at night. The ring button fires buzzer and LED together — but only once the LDR sees darkness. In daylight the button does nothing. 30 min · ●●●○○ Alley Lamp Automatic Night Light with a push-button override. Dark room OR button press fires the lamp — a wired-OR built straight onto the transistor's base. 30 min · ●●●○○ The Upside-Down Transistor A PNP transistor switches the + side of a lamp and turns on when you pull its base DOWN. Same button, same LED, whole circuit flipped. 30 min · ●●●○○

L4 Motion

Make things spin, wobble, and go.

Puff Button First Spin with the slide swapped for a push button. Press for a spurt of breeze, let go and it stops — a dust puffer for a keyboard or camera lens. 10 min · ●○○○○ First Spin Your first motor. A switch, a coil, and a diode that catches the voltage kick when the current stops. 15 min · ●●○○○ Safety Blender A slide lid switch and a push run button, both in series with the motor. Fan only spins when the lid is on AND your finger is on the button. 15 min · ●●○○○ Handheld Fan Press the button, the fan spins. A tiny finger current commands a hundred-milliamp motor through a transistor. 20 min · ●●●○○ Sunrise Fan Sunrise Alarm with the LED swapped for a motor. The sun rises, the fan starts — an automatic wake-you-up desk breeze. 25 min · ●●●○○ Panic Fan Two buttons, either one fires the fan. Panic Doorbell wearing a motor — an OR gate that spins. 20 min · ●●●○○ Party Spinner One button, three mouths: a spinning motor, a red LED, and a buzzer all fire together. One transistor drives them all. 25 min · ●●●○○ Twin Wheels Two motors from one button — a Level 9 robot drivetrain, five levels early. 25 min · ●●●○○ Dial-a-Spin Dial-a-Brightness with a motor instead of an LED. Twist the knob and watch the fan speed slide from full spin to a slow crawl. 20 min · ●●●○○ Trip Wire Fan Trip Wire Alarm's brain wearing a motor. The wire is intact — the fan is silent. Snap it — the fan spins as the alarm. 25 min · ●●●○○ Sun Beacon Sunrise Fan with a second lane — a yellow LED lights and a motor spins together the moment daylight hits the sensor. One brain, two mouths. 25 min · ●●●○○ Dusk Fan Sunrise Fan's mirror image — the room gets DARK and the fan spins. A bedside cooling breeze that starts as the lights go out. 25 min · ●●●○○ Warm Hand Fan A little desk fan that starts when you cup your palm over the sensor. Warm-Hand Alarm's brain, motor mouth. 25 min · ●●●○○

More projects land level by level. Every one opens in the Workbench before you touch a real part.