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 is from an American 80's documentation. The transistor is general purpose,...
We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an...
This old configuration, using a unijunction transistor (UJT) controls a LED than blinks if an...