This alarm circuit with NC sensors in series was taken from an article in Radio Electronics magazine from May 1971. The SCR can be any of the 106 series.
This antenna for the frequencies 146 or 440 MHz was found in a magazine 73 for Amateur Radio of...
We found this circuit in an 80's EDN. The circuit makes use of a MAX680, being given a table with...
This circuit was found in a 1986 publication. However, it can still be easily assembled, as the...