Found in 1980s Electronic Engineering, this circuit uses common phototransistors as sensors. The circuit is CMOS using an integrated 4011.
The cut-off frequency of the filter shown in the figure can be adjusted to values between...
This circuit was found in a Popular Electronics from the 90s. The components used are all common...
This circuit uses a dual floodgate MOSFET not very easy to obtain today. Its handling is very...