An interesting configuration shown by Figure 1 can be used to generate a continuous tone in a small loudspeaker or even in a piezoeletric transducer. The frequency is determined by the time constant given by the inductance of the relay’s coil and the capacitance, C. Capacitors rated between 0.047 and 470 nF can be used experimentally in a particular application. Any small loudspeaker can be wired in series with the relay. Piezoelectric buzzers must be Wired in parallel with the coil.
Figure 1 – The passive buzzer.
