Found in old American documentation, this receiver transmits signals via the power grid. We can use it on links or remote control. The components admit equivalents.
This circuit reproduces the dial noise in a small speaker. The transistor can be a general-purpose type....
We found this circuit in an 80's schematic. The circuit uses LEDs in series with zeners to...
This circuit turns off after a time given by capacitor C1. This component can have from 1 to 1,000...