Amplifier Circuit DiagramsAudio Circuit DiagramsOscillators Circuit Diagrams

Steam Whistle Schematic Circuit Diagram

Six Oscillators Generating Complex Square Wave Signals

This innovative circuit incorporates six square wave oscillators, each producing its distinct frequency. Square waves, composed of numerous harmonics, can be combined to create a signal with a vast range of frequencies. The resulting sound closely resembles that of a steam whistle. This circuit finds applications in modeling and sound studios. Remarkably, it utilizes only two ICs for its operation. The initial IC, a 40106, houses six Schmitt triggers, all functioning as oscillators. Varied frequencies are achieved by utilizing diverse feedback resistors.

Complex Sound Generation through Six Oscillators

Utilizing six square wave oscillators, this circuit generates a complex audio signal. Square waves, rich in harmonics, are blended to produce a signal resembling a steam whistle’s sound. This versatile circuit finds utility in modeling and sound studio environments. Surprisingly, the circuit relies on just two ICs for its operation. The primary IC, a 40106, integrates six Schmitt triggers, all configured as oscillators. The incorporation of different feedback resistors enables the generation of varied frequencies.

Steam Whistle Schematic Circuit Diagram

Signal Mixing and Amplification

The signals generated by the Schmitt triggers are combined using resistors and then amplified by IC2, specifically an LM386. This integrated circuit has the capability to deliver approximately 1 watt of audio power, which proves adequate for most applications. By excluding R13 and all components after P1, the output can be linked to a more robust amplifier, allowing the creation of an exceedingly loud steam whistle effect. The signal’s ‘frequency’ can be fine-tuned using P2, while P1 governs the volume.

LM386 Power Amplifier Functionality

The LM386 serves as a power amplifier, meticulously crafted for low voltage applications in the consumer sector. Internally, the gain is preset to 20 to minimize external component requirements. However, attaching an external resistor and capacitor between pins 1 and 8 allows the gain to be adjusted within the range of 20 to 200. The inputs are grounded, and the output automatically biases to half the supply voltage. Remarkably, the quiescent power consumption is merely 24 milliwatts when operating from a 6-volt supply, making the LM386 exceptionally suited for battery-powered operations.


  • Battery operation
  • Minimum external parts
  • Wide supply voltage range: 4V–12V or 5V–18V
  • Low quiescent current drain: 4mA
  • Voltage gains from 20 to 200
  • Ground-referenced input
  • Self-centering output quiescent voltage
  • Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8Ω, PO = 125mW, f = 1kHz)
  • Available in an 8-pin MSOP package


  • AM-FM radio amplifiers
  • Portable tape player amplifiers
  • Intercoms
  • TV sound systems
  • Line drivers
  • Ultrasonic drivers
  • Small servo drivers
  • Power converters

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