This circuit for the 60 kHz range was found in 73 magazine and published in 1995. The circuit uses a ferrite rod. Note the direction of the coil windings.
We found this circuit in a 2005 Linear Technology manual. The resistor is calculated for the...
The frequency of this circuit is determined by the 100 uF capacitors. These components can be...
This circuit appeared in the July 1969 issue of Radio Electronics magazine. The sensor is an LDR....