This alarm circuit with sensors in series was found in the Electronics Now magazine of June 1994. The circuit is powered according to the relay used.
This circuit is from a documentation from the 60s. The circuit can be built with transistors like...
Found in a 1966 General Electric documentation, this dimmer should only be used with incandescent...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...