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Built-in project · no microcontroller

Doorbell

A pushbutton lifts the 555 out of reset and a 4 Hz astable beeps the buzzer. There is no microcontroller in it: the simulator solves the 7 parts as a circuit, so it runs the moment you press Run, and nothing needs compiling.

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Doorbelllive0.000 s 0.00x
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The circuit itself, running here on the simulator. Press what can be pressed; click anything else to open it in the editor.

How it works

There is no microcontroller in this one, so nothing is compiled: the simulator solves the circuit itself. The file in the editor is the notes that come with it.

sketch.ino
// A doorbell: a button, a 555 and a buzzer.
//
// The buzzer here is an active one: it has its own oscillator inside, so DC
// across it makes its note and nothing across it is silence. The 555 is not
// making the tone, it is making the rhythm: about four pulses a second, so the
// bell beeps instead of droning.
//
//   f = 1.44 / ((R1 + 2 R2) C) = 1.44 / ((10k + 94k) x 3.3 uF) = 4.2 Hz
//
// Hold the pushbutton while it runs. It pulls RESET (pin 4) up to 5 V; let go
// and the 10 k resistor pulls RESET back to ground, which clamps the output
// low whatever the capacitor is doing.
//
// The buzzer is wired straight to the output with no series resistor, on
// purpose: it is a 160 ohm load that needs most of the supply across it to
// sound at all. Put the usual 220 ohm "LED resistor" in front of it and the
// divider leaves 2.1 V across the element, and it goes quiet.

Parts list

9 parts, plus the jumper wires. Every one is in the editor's parts bin.

How it is wired

6 connections, pin by pin, read from the circuit itself. Each line is one set of pins joined together, by a jumper wire or a breadboard strip.

  • 5 V: Resistor, 10k Ω (1) pin 1; NE555 timer pin VCC; Pushbutton pin 2a
  • Ground: NE555 timer pin GND; Capacitor, 3.3 µF pin 2; Resistor, 10k Ω (2) pin 2; Buzzer pin 2
  • Resistor, 10k Ω (1) pin 2; NE555 timer pin DIS; Resistor, 47k Ω pin 1
  • NE555 timer pin TRIG; NE555 timer pin THR; Resistor, 47k Ω pin 2; Capacitor, 3.3 µF pin 1
  • NE555 timer pin OUT; Buzzer pin 1
  • NE555 timer pin RESET; Resistor, 10k Ω (2) pin 1; Pushbutton pin 1b

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