The frequency of each note depends on R2, which must be replaced by a keyboard. The circuit is from Radio Electronics from April 1980. The power supply is 9 V for the amplifier used.
The circuit shown in the figure can be used as an indicator of presence and high voltage in a...
This circuit uses the 2N626, the first commercial Darlington transistor. We found it in Radio...
This circuit can generate signals from 80 to 800 Hz with an amplitude of 0.3 V. We find it in a...