Rotating a small engine with the help of a steering wheel produces a sound similar to a siren which will be amplified by an electronic circuit. This project can be used for many interesting applications such as installation on bicycles, toys or for special effects in studios and recordings.
The circuit consists of a common direct current motor that, when turned, works like a small dynamo producing a current whose frequency depends on its speed. This current is amplified by a circuit with two complementary transistors that directly drive a small speaker.
In the basic version the circuit is powered with 3 or 6 V, but to get higher volume we can even feed it with 12 V.
The diagram in figure 1 shows that there are few components used.
The circuit is mounted on a terminal strip. For 12 V power supply transistor Q2 must be mounted on a heat radiator. For higher performance the speaker should be of good performance. In figure 2 we have the strip mounting.
For a better sound effect, which resembles a bombing alert siren, as used in World War II, we can attach a small flywheel to the engine shaft, as shown in Figure 3.
Boosting this steering wheel, the sound effect will be interesting.
Material list
Q1 - BC548 - General Purpose NPN Transistor
Q2 - TIP31 - NPN Power Transistor
M - small direct current motor
S1 - Single Switch
B1-3V to 12V - batteries or source
FTE - Heavy 4 or 8 ohm speaker
R1 - 2.2 M ohm x 1/8 W - resistor - red, red, green
C1-220 nF to 470 nF - Ceramic or Polyester Capacitor
Miscellaneous: battery holder or power supply, handwheel, terminal bridge, heat radiator, wires, soldering, etc.
