Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics magazine. It covers frequencies in the range of 45 Hz to 45 kHz.
Other CMOS gates can be used in this sensor, which we found in the July 1995 Electronic Now...
This circuit is from the American magazine that no longer exists Science & Electronics,...
Using the 4046 PLL we found this circuit in the December 1989 Radio Electronics. The circuit...