We found this circuit in the August 1990 issue of Radio Electronics magazine. The two-digit circuit uses a pressure sensor and is powered by a 9V battery.
This is a MOSFET version of a grid dip meter for frequencies between 1.8 MHz and 150 MHz,...
This circuit has a sensitivity of 2uW. We found it in documentation from the 1980s. The integrated...
The sensors in this circuit are photodiodes with filters. The circuit is suggested by the National...