We found this receiver circuit for modulated light in a 90s Popular Electronics. Equivalent audio amplifiers can be used. Transistors are commonly used.
This interesting circuit of a 1988 documentation consists of a mouse trap where the sensor is left to...
This circuit is more elaborate than the previous one, employing an integrated amplifier circuit of the...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...