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.
This circuit was obtained from a Popular Electronics of 1994. The magazine no longer exists in its...
This circuit is from Motorola documentation on 1976 power devices. SCRs are powered according to...
This latching alarm using SCR was found in a Popular Electronics from 1992. The circuit triggers a...