This circuit was found in a 90s Wels' Think Tank. The frequency depends on C2 and R3. The handset or speaker must be at least 80-ohm. Observe the low supply voltage.
The output voltages of this power source are selected by a switch according to the capacitors. The...
This circuit is from a 90s Popular Electronics. The circuit employs a ZN461E that is not a common...
This circuit was found in Siliconix documentation from the 1980s. Equivalent operational...