This didactic project can be used in elective subjects and technical courses as practical assembly. Thus, we give the version in an assembly both in terminal bridge and in contact array.
This circuit consists of a very low frequency oscillator using complementary transistors.
The circuit can be powered by voltages from 3 to 6 V and directly excites a small speaker.
The loudspeaker then produces sound pulses whose cadence (frequency) can be set in a potentiometer.
All components used are common and inexpensive.
In figure 1 we have the complete diagram of the metronome.
The terminal strip mounting is shown in figure 2.
The assembly using an array of contacts is shown in figure 3.
Capacitor C1 can be changed over a wide range of values depending on the desired frequency range.
The speaker can be 4 or 8 ohms with 2.5 to 10 cm in diameter.
Material list
Q1 - BC548 - NPN general purpose transistor
Q2 - BC558 - general purpose PNP transistor
FTE - 4 or 8 ohm speaker
P1 - 1M - potentiometer
R1 - 10 k ohms x 1/8 W - resistor - brown, black, orange
R3 - 1k ohms x 1/8 W - resistor - brown, black, red
C1 - 10 uF - electrolytic capacitor - 6 V or more
C2 - 100 uF x 6 V - electrolytic capacitor
S1 – On-Off switch
B1 - 3 to 6 V - 2 to 4 small batteries
Several:
Terminal strip or contact array, wires, solder, etc.
