The sensor used in this circuit is uncommon today, however equivalent types can be tried. The comparator also supports modern equivalents. The circuit is from 80's documentation.
The first circuit, shown in the figure, generates a stepped signal whose frequency depends on the...
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
The operational used is like the 741 and the voltage gain is unitary. The circuit is from the...