part · Level 2 · Sound · output
Active vs passive buzzer explained
Active buzzer (3–5 V) — Give it power, it beeps. It makes its own tone inside.
What it is
A buzzer turns electricity into sound. Inside the little black can is a piezo disc — a ceramic that flexes when voltage is applied — and, in an active buzzer, a tiny oscillator circuit that wobbles that voltage a couple of thousand times a second on its own. Give it steady DC and it beeps at its built-in pitch, usually around 2–3 kHz.
A passive buzzer has the disc but no oscillator. It stays silent on DC; you have to feed it a wobbling signal from a 555 timer or a microcontroller, and in return you choose the pitch. Yours is active: simpler, louder for its size, one note.
It has polarity: the longer leg (and the leg by the + mark on the top) goes toward the battery's red wire.
How it works
Because the buzzer contains its own electronics, it limits its own current. On the 4.5 V pack it draws about 30 mA, which behaves like a load of 4.5 V ÷ 0.030 A ≈ 150 Ω. That is why, unlike an LED, it connects straight across the supply with no resistor: the 30 mA is what it wants, and nothing in it can run away.
Add a resistor anyway and you get a volume control. With 1 kΩ in series the current falls to 4.5 ÷ (1000 + 150) ≈ 3.9 mA — a whisper (the Two-Tone Doorbell). With a 10 kΩ pot at maximum it is 4.5 ÷ 10 150 ≈ 0.44 mA, effectively silent (the Whisper Alarm).
A transistor can switch it: the 2N2222 handles up to 600 mA, so 30 mA is trivial, and the base needs only around 30 ÷ 200 = 0.15 mA to do it. That is the Cookie Jar Alarm and its cousins.
Battery life at full volume: 2000 mAh ÷ 30 mA ≈ 65 hours of continuous noise — but an alarm that is silent until triggered draws essentially 0 mA between events.
The numbers
| Operating voltage | 3–5 V — works on the 4.5 V pack |
|---|---|
| Current | ≈ 30 mA — at 4.5 V; behaves like ~150 Ω |
| Polarity | long leg / + mark to + |
| Tone | fixed, ≈ 2–3 kHz — set inside — passive buzzers let you choose |
| Current with 1 kΩ in series | ≈ 3.9 mA — quiet mode |
See it working
The Panic Doorbell circuit, simulated live. Open it on the Workbench to change anything.
simulating…
Mistakes everyone makes
- Backwards. Silent, and some active buzzers are damaged by reverse voltage over time. Fix: + leg toward the red wire; check the sticker on top.
- Adding a 220 Ω "like an LED". It still works but at 4.5 ÷ 370 ≈ 12 mA it is noticeably quieter. Fix: no resistor unless you want quiet.
- Trying to play a tune. An active buzzer has one note. Fix: a passive buzzer or piezo disc driven by a 555 or microcontroller.
- Holding it to your ear. It is loud at close range. Fix: don't.
- Sharing a lane with an LED without its own resistor. The LED sees the buzzer's 4.5 V and pops. Fix: separate lanes, 220 Ω on the LED lane.
Questions people ask
- What is the difference between an active and a passive buzzer?
- An active buzzer has an oscillator built in and beeps on plain DC at one fixed pitch. A passive buzzer needs a changing signal from a timer or microcontroller, which lets you pick the note.
- Does a buzzer need a resistor?
- An active buzzer does not — its internal circuit sets the current (about 30 mA at 4.5 V). A series resistor is optional as a volume control: 1 kΩ drops it to about 4 mA.
- Which leg of a buzzer is positive?
- The longer leg, usually next to a + printed on the top of the case. It goes toward the battery red wire.
Projects that use this part
- 🔔 Door Buzzer — Your first sound circuit — a real doorbell for your bedroom door. L2 · 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. L2 · 15 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
- 🔔 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
- 🍪 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. L3 · 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. L3 · 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. L3 · 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. 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
- 🎉 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
verified against: SparkFun — Buzzer Basics · SparkFun — Transistors