Found in a Popular Electronics from the 90s, this circuit can act as a transmitter for an audio link. The output transistor admits a higher power equivalent, depending on the LED.
In the figure we have a piezoelectric transducer drive circuit that can be used in conjunction with the...
This circuit is from a Ferranti publication of 1968. The circuit generates a signal according to the...
This is one of the possible triac power control configurations using as a trigger element a...