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 1967 Philips circuit recognizes a light signal (visible or infrared) modulated by tone. The...
This circuit makes use of the LM11, 112 or 113 operatives and was found in a 1980s documentation. The...
Found in a 1969 Ferranti documentation, this circuit uses only bipolar transistors from that time....