This circuit was found in a 90s Popular Electronics. The sensors can be common speakers that reach from 15k to 25 kHz, such as piezoelectric tweeters.
This circuit multiplies the input resistance of an operational amplifier. As the indicated...
This conventional flip-flop configuration with two transistors was found in documentation from the...
The input impedance of this amplifier is of the order of 1014 being the same indicated for pH...