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.
Found in old documentation, this circuit is the receiver for the previous circuit. Components are...
We found this circuit in the 1994 Linear Applications Handbook by National Semiconductor. The...
This circuit switches the capacitors of a digital filter with the 4046 IC (PLL). The circuit was...