circuit produces the famous Big Ben sound. It produces
the "ding dong" sound when switched ON.
Basically the circuit alternates between two frequencies
which are adjustable. This produces the "ding-dong"
The first IC(left) oscillates at about 1Hz. The second
IC's tone is modulated by the changing voltage at the
output of the first IC.
IC determines how fast the changeover from one frequency
to the other takes place and second IC determines the
tone of the final output.
By varying the VR1, the changeover rate can be adjusted.
By varying VR2 the tone can be adjusted.