The movement of mechanical arms, robots and other automatisms studied in mechatronics is obtained through silent motors.
In a demonstration it may be interesting to have some kind of sound effect that mimics the noise of an engine in a stronger way, in order to give more realism to the operation of such devices.
The circuit we propose is simple and can be powered with voltages from 3 to 6 volts.
The efficiency of the circuit is very good and the small speaker can be built into the automation or installed in a suitable box.
The circuit also has a frequency setting that serves as an accelerator for the purpose and that can be within reach of the operator or even be coupled to some automatic activation device.
Basically the design consists of an oscillator where the frequency is either determined by C1 (which can be altered) or by the setting of P1 (acting as "throttle").
In figure 1 we have the complete diagram of this apparatus.
In figure 2 we show the arrangement of the components in a terminal strip which is the simplest and most immediate version mainly for beginners.
The transistors allow equivalents and even Q2 can be a BD136 or TIP32 and the 12 V powered circuit for higher power.
In this case, however, power must come from source or battery, since a simple set of batteries would not be able to supply the required energy.
The speaker can be 5 to 10 cm with 4 or 8 ohms of impedance.
The resistors are 1/8 W or larger and the electrolyte is 12 V.
To test the appliance, just turn on the power.
Sound pulses should occur at a greater or lesser speed as we adjust the potentiometer.
Adjust to get the sound equivalent to a motor.
Proven operation is just to install the set in a box and use the device in the best way, embedding it in your robotics or mechatronics assembly or wherever you want.
Parts List
Q1 - BC548 or equivalent - general purpose NPN transistor
Q2 - BC558 or equivalent - general purpose PNP transistor
FTE - 4 or 8 ohms - small speaker
S1 - Single switch - optional
B1 - 3 or 6 volts - 2 or 4 batteries - see text
P1 - 1 M ohms - potentiometer
R1 - 10 k ohms - brown, black, orange
R2 - 1 k ohms - brown, black, red
C1 - 10 uF / 12 V - electrolytic capacitor
Miscellaneous:
Terminal strip, mounting box, two or four battery holder (optional), button for potentiometer, wires, solder, etc.
