We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the transistor BC558. The relay has an operating voltage according to the power supply.
This high-performance circuit was found in the 1982 SGS Linear Integrated Circuits Manual. The...
This circuit for audio applications was found in an English magazine from the 80's. The circuit...
The circuit presented uses an integrated circuit Sanyo, not very common in our day. This amplifier provides...