This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and the components of the T filter and the multivibrator can be changed to obtain the exact tone.
This oscillator is enabled when a high level is applied to the control input. The operating...
This circuit uses two oscillators to produce a sound that seems the sound of a ring-bell. The...
Found in a Popular Electronics from the 9s, this circuit has output for RS-232 interfaces and current...