555 Timer Tone Generator: Circuit, Measurements and Online Simulator

To build this 555 Timer Tone Generator circuit you need a bench power supply, an oscilloscope, a 555 timer, a 1 kΩ resistor, a 6.8 kΩ resistor, a 220 nF ceramic capacitor, a 100 µF electrolytic capacitor, a 47 Ω resistor and a speaker 8 Ω. A 555 astable at about 440 Hz (the note A) drives an 8 Ω speaker through a 100 µF coupling capacitor. Turn the sound on to hear it. Make the 18 connections in the wiring table, press Run, and with sound on: you hear about 440 Hz. Change R2 to 3.3 k for a higher note, or C to 22 n for a much higher one. The scope shows the square wave and the capacitor sawtooth.

Open this circuit in the free Electronics bench simulator

Parts list

Qty	Part	What it does
1	Bench Power Supply	Set the voltage and a current limit. It holds the voltage (CV) until the load wants more than the limit, then holds the current (CC). + and − float; GND is earth.
1	Oscilloscope	Two channels against earth (GND). Turn TIME/DIV and VOLTS/DIV to fit the wave, set the trigger level to steady it, and read Vpp, RMS and frequency. X-Y mode draws Lissajous figures. Choose a digital (DSO) or phosphor (CRO) screen.
1	555 Timer	The classic timer. Astable: R1 from VCC to DIS, R2 from DIS to THR+TRIG, C to GND — f ≈ 1.44 / ((R1 + 2·R2)·C). Tie RESET to VCC.
1	1 kΩ resistor	Limits current. 220 Ω in series with an LED; 10 kΩ as a pull-up or pull-down.
1	6.8 kΩ resistor	Limits current. 220 Ω in series with an LED; 10 kΩ as a pull-up or pull-down.
1	220 nF ceramic capacitor	Stores charge; blocks DC, passes AC. With a resistor it sets a time constant τ = RC (1 kΩ × 1 µF = 1 ms). Not polarised.
1	100 µF electrolytic capacitor	A large, polarised capacitor for smoothing supplies: the stripe marks − . Reverse it, or exceed its voltage rating, and it fails.
1	47 Ω resistor	Limits current. 220 Ω in series with an LED; 10 kΩ as a pull-up or pull-down.
1	Speaker 8 Ω	An 8 Ω loudspeaker: you hear whatever AC drives it. Feed it from the function generator, a 555, or a pin through a transistor — and a capacitor to block DC.

Wiring

#	From	To
1	Bench Power Supply +	555 Timer VCC
2	Bench Power Supply +	555 Timer RESET
3	555 Timer GND	Bench Power Supply -
4	Bench Power Supply -	Bench Power Supply GND
5	Bench Power Supply +	1 kΩ resistor leg 1
6	1 kΩ resistor leg 2	555 Timer DIS
7	555 Timer DIS	6.8 kΩ resistor leg 1
8	6.8 kΩ resistor leg 2	555 Timer THR
9	555 Timer THR	555 Timer TRIG
10	555 Timer THR	220 nF ceramic capacitor 1
11	220 nF ceramic capacitor 2	Bench Power Supply -
12	555 Timer OUT	100 µF electrolytic capacitor +
13	100 µF electrolytic capacitor -	47 Ω resistor leg 1
14	47 Ω resistor leg 2	Speaker 8 Ω +
15	Speaker 8 Ω -	Bench Power Supply -
16	555 Timer OUT	Oscilloscope CH1
17	555 Timer THR	Oscilloscope CH2
18	Bench Power Supply -	Oscilloscope GND

Step by step

Open the electronics bench. Open the BitForBytes Embedded Lab in your browser. A circuit with no microcontroller runs on the analog bench: no install or account is needed.
Add the parts. Add a bench power supply, an oscilloscope, a 555 timer, a 1 kΩ resistor, a 6.8 kΩ resistor, a 220 nF ceramic capacitor, a 100 µF electrolytic capacitor, a 47 Ω resistor and a speaker 8 Ω from the parts palette (Instruments, Power, Passive and Semiconductors).
Wire 1. Connect Bench Power Supply + to 555 Timer VCC.
Wire 2. Connect Bench Power Supply + to 555 Timer RESET.
Wire 3. Connect 555 Timer GND to Bench Power Supply -.
Wire 4. Connect Bench Power Supply - to Bench Power Supply GND.
Wire 5. Connect Bench Power Supply + to 1 kΩ resistor leg 1.
Wire 6. Connect 1 kΩ resistor leg 2 to 555 Timer DIS.
Wire 7. Connect 555 Timer DIS to 6.8 kΩ resistor leg 1.
Wire 8. Connect 6.8 kΩ resistor leg 2 to 555 Timer THR.
Wire 9. Connect 555 Timer THR to 555 Timer TRIG.
Wire 10. Connect 555 Timer THR to 220 nF ceramic capacitor 1.
Wire 11. Connect 220 nF ceramic capacitor 2 to Bench Power Supply -.
Wire 12. Connect 555 Timer OUT to 100 µF electrolytic capacitor +.
Wire 13. Connect 100 µF electrolytic capacitor - to 47 Ω resistor leg 1.
Wire 14. Connect 47 Ω resistor leg 2 to Speaker 8 Ω +.
Wire 15. Connect Speaker 8 Ω - to Bench Power Supply -.
Wire 16. Connect 555 Timer OUT to Oscilloscope CH1.
Wire 17. Connect 555 Timer THR to Oscilloscope CH2.
Wire 18. Connect Bench Power Supply - to Oscilloscope GND.
Run and measure. Press Run with sound on: you hear about 440 Hz. Change R2 to 3.3 k for a higher note, or C to 22 n for a much higher one. The scope shows the square wave and the capacitor sawtooth.

Lab sheet

// Electronics bench: 555 oscillator as a tone generator
//
// f = 1.44 / ((R1 + 2·R2) · C) = 1.44 / ((1 k + 2 × 6.8 k) × 220 nF) = 448 Hz.
// The 100 µF capacitor blocks the DC so only the tone reaches the speaker,
// and the 47 Ω resistor limits the current the 555 output has to supply.

What to try

Press Run with sound on: you hear about 440 Hz. Change R2 to 3.3 k for a higher note, or C to 22 n for a much higher one. The scope shows the square wave and the capacitor sawtooth.

Frequently asked questions

How do I wire the 555 Timer Tone Generator circuit?

Make 18 connections: Bench Power Supply + to 555 Timer VCC; Bench Power Supply + to 555 Timer RESET; 555 Timer GND to Bench Power Supply -; Bench Power Supply - to Bench Power Supply GND; Bench Power Supply + to 1 kΩ resistor leg 1; 1 kΩ resistor leg 2 to 555 Timer DIS; 555 Timer DIS to 6.8 kΩ resistor leg 1; 6.8 kΩ resistor leg 2 to 555 Timer THR; 555 Timer THR to 555 Timer TRIG; 555 Timer THR to 220 nF ceramic capacitor 1; 220 nF ceramic capacitor 2 to Bench Power Supply -; 555 Timer OUT to 100 µF electrolytic capacitor +; 100 µF electrolytic capacitor - to 47 Ω resistor leg 1; 47 Ω resistor leg 2 to Speaker 8 Ω +; Speaker 8 Ω - to Bench Power Supply -; 555 Timer OUT to Oscilloscope CH1; 555 Timer THR to Oscilloscope CH2; Bench Power Supply - to Oscilloscope GND.

What parts do I need for the 555 Timer Tone Generator?

A bench power supply, an oscilloscope, a 555 timer, a 1 kΩ resistor, a 6.8 kΩ resistor, a 220 nF ceramic capacitor, a 100 µF electrolytic capacitor, a 47 Ω resistor and a speaker 8 Ω.

Can I simulate the 555 Timer Tone Generator online for free?

Yes. The BitForBytes Embedded Lab solves the circuit in time, the way SPICE does (nodal analysis with real diode, transistor and capacitor models), and gives you a bench power supply, function generator, oscilloscope and multimeter to measure it — free, in the browser.

What does this circuit show?

A 555 astable at about 440 Hz (the note A) drives an 8 Ω speaker through a 100 µF coupling capacitor. Turn the sound on to hear it.