skill

Switches

Breaking and completing loops on purpose — the root of all control.

first shows up at Level 1 · Light

See it working

simulating…

Switch closed — loop complete, LED on. Open the circuit, tap the switch to pop a gap in the loop, and the LED goes dark no matter where in the loop that gap sits. 🔧 Open this circuit in the Workbench →

A switch is the simplest control device in electronics: it's a gap you can open and close on purpose. Push the button and the gap closes: current flows, so the LED lights. Let go and the gap opens. The loop breaks, and the LED goes dark.

The two big families

Momentary switches (push buttons): they're only "on" while you're pressing them. Great for doorbells, game controllers, "fire" buttons.
Toggle switches (slide, rocker, toggle): they stay in the position you put them. Great for on/off power switches.

Position matters

Where you put the switch changes what it controls, not whether it works. Since a broken loop stops everything, a single switch anywhere in the loop turns the whole circuit off. That's why the switch in a flashlight can be at the tail end and still cut power to the bulb at the front.

Once you're comfortable with switches, transistors will feel familiar — a transistor is just an electronic switch that a tiny current can flip instead of your finger.

Projects that teach this

First Light Build a real flashlight circuit and learn why every circuit is a loop. L1 15 min Morse Code Messenger A push button, an LED, and a secret code — send real messages with light. L1 20 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. L1 10 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. L1 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. L1 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 a clear, steady glow. L1 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. L1 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. L1 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. L1 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. L1 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. L1 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. L1 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. L1 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. L1 15 min The Vault Two buttons, one loop — the LED only lights when BOTH are pressed at the same time. L1 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. L1 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. L1 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. L1 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. L1 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. L1 20 min Door Buzzer Your first sound circuit — a real doorbell for your bedroom door. L2 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. L2 10 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. L2 15 min Panic Doorbell Two buttons wired so either one fires the same buzzer and light — your first OR gate. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 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. L2 15 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. L3 25 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. L3 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. L3 25 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. L3 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. L3 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. L3 30 min 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. L4 10 min First Spin Your first motor. A switch, a coil, and a diode that catches the voltage kick when the current stops. L4 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. L4 15 min Handheld Fan Press the button, the fan spins. A tiny finger current commands a hundred-milliamp motor through a transistor. L4 20 min Panic Fan Two buttons, either one fires the fan. Panic Doorbell wearing a motor — an OR gate that spins. L4 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. L4 25 min Twin Wheels Two motors from one button — a Level 9 robot drivetrain, five levels early. L4 25 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. L4 25 min The Two-Key Lock Two NAND gates make an AND: the LED lights only while BOTH buttons are down. The first logic chip, and the reason NAND is called universal. L6 45 min The Alarm That Remembers Two NAND gates wired into each other make a memory. Tap SET and the red LED stays on after you let go, until someone presses RESET. L6 45 min The Two-Switch Hall Light A light with a switch at each end of the hall: flip either and the light changes. Four NAND gates in one CD4011 make an XOR. L6 60 min