What a 220 ohm resistor is for

Projects that use this part

• 🔦 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
• 🎈 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. L1 · 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. L1 · 15 min
• 🚦 Tabletop Traffic Light — Three LEDs on three parallel lanes, all lit by one switch — build a tabletop traffic light and discover parallel circuits. L1 · 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. 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
• 🔴 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
• 🔦 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
• 🧪 The Brightness Lab — Run a real experiment: predict, measure with your eyes, and prove Ohm's law. L1 · 30 min
• 🔔 Door Buzzer — Your first sound circuit — a real doorbell for your bedroom door. L2 · 20 min
• 🎛️ Dial-a-Brightness — Twist a knob and watch the LED fade up and down — your first "how much" input. L2 · 20 min
• 🔧 Continuity Tester — Your first real tool — two probe wires that beep and light up whenever the tips touch anything that conducts. L2 · 20 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
• 🖐️ 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
• 🎵 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
• 🌙 Automatic Night Light — A light that switches itself on when the room gets dark — no hands, no code. L3 · 35 min
• 🌅 Sunrise Alarm — The night light — flipped. Swap two parts and the LED wakes up with the sun instead. L3 · 25 min
• 🌡️ Warm Hand Alarm — Cup your hand over the sensor and the LED lights up — a thermometer that turns into a switch. L3 · 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. L3 · 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. 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
• 🌇 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. L3 · 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. L3 · 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. L3 · 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. 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
• 🙃 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. L3 · 30 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
• 🌅 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. L4 · 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. L4 · 25 min
• ⚖️ The 3.3-Volt Rule — A zener diode holds 3.3 V for the LED no matter what the 9 V battery wants. Flick the switch to add a second load and watch the zener share. L5 · 30 min
• 🪶 The Switch That Uses No Current — A MOSFET turns the LED fully on, yet its gate draws nothing. Hold the button, then tap the 10 kΩ to make it 100 kΩ and see the gate still win. L5 · 30 min
• 🌙 The Night Gate — A night light switched by a MOSFET. The gate takes no current, so the moment it turns on is plain voltage-divider math you can work out exactly. L5 · 30 min
• 🔋 The Zener Battery Tester — A zener in series with an LED makes it ignore the first 3.3 V. A fresh 9 V lights it; a run-down battery barely can. A sharper gauge than a bare LED. L5 · 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 Four-Step Chaser — A 555 ticks five times a second and a CD4017 counter walks the light from LED to LED, round and round. Hold a button and the chase freezes. L6 · 60 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