This circuit was found in the July 1978 issue of Radio Electronics magazine. The circuit uses a common digital voltmeter as the indicator. The sensors are integrated circuits of the time.
This adapter circuit was found in a 1990 documentation. It is possible to connect a telephone line...
This receiver circuit was found in a Hands On Electronics from the 90s. The circuit uses a PLL...
The operational amplifier of this low current source may be any of the JFET type. The output...