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.
The circuit shown in the figure has elements for maximum gain at maximum speed. By setting the...
This instrument, based on a 555, measures frequencies up to 1 kHz, but its scale can be modified by...
Using a CA3130 operational amplifier, this circuit was found in an English publication from 1977....