This circuit allows you to read resistors up to 20 M ohms, converting it into voltage. The circuit is from the 90s. The operational ones used admit modern equivalents.
This circuit produces pulses of great intensity and short duration at a frequency of approximately 1 kHz....
In the figure we show how to implement a voltage reference with the ON Semiconductor rail-to-rail...
This preamplifier for record players with crystal capsules was found in Radio Electronics magazine...