Sound effects generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators
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We bring to your attention a scheme that can amuse children. It can generate police car siren sounds, birds chirping, space ship sounds, etc. In addition, the circuit can be used in doorbells or used in alarms. This circuit is easy to make and contains inexpensive components.
The circuit consists of four parts: a binary counter, a digital-to-analogue converter (DAC), a voltage controlled oscillator (VCO), and an audio output amplifier. The speed at which the counter counts depends on the frequency of the VCO at its output, and the frequency of the VCO in turn is determined by the counter. This feedback loop forms the output signal.
According to the circuit shown in the figure, the initial frequency of the oscillator assembled on the elements IC2a and IC2b is set by the potentiometer VR1 and the capacitor C1. Initially, the oscillator operates at a relatively low frequency, the frequency gradually increases as the voltage at the DAC output increases.
(click to enlarge)
The DAC is a group of resistors R1...R8, connected to the output of the counter IC1, providing the base current of the transistor TR1. When all outputs of IC1 are set low, a small current will flow through the base of transistor TR1, hence the control voltage will be low. As the counter outputs appear logic ones, the base current of the transistor TR1 will increase, and consequently the output frequency of the VCO will increase.
The VCO itself is assembled on the elements IC2a, IC2b, TR1, diodes D2 ... D5, capacitor C1, resistors R10 and VR1. The diode bridge works basically as a voltage controlled resistor.
The buffer amplifier is assembled on four IC2 elements connected in parallel, the output of the amplifier is connected to the loudspeaker LS1 through the capacitor C2. The output signal level is sufficient for experimental purposes; to obtain a greater volume, the output amplifier can be replaced with a conventional ULF.
The connections on the circuit are made in the usual way, the wiring is not critical, but make sure that the polarity of the power supply is connected to the chips correctly. By pressing the button S1, you will hear a sound, which will depend on the position of the potentiometer VR1. To change the effect, press the S1 button.
Author: Craig Kendrick Sellen, Carbondile, Pennsylvania, USA
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