This circuit uses an HA2400 consisting of 4 digitally controlled operational amplifiers. The circuit is from a Radio Electronics magazine from March 1980. The power supply must be symmetrical.
Using components from the era, this 90's EDN circuit is used in analog to digital conversion...
Found in an American publication from the 90s, this circuit allows the supply of 3, 6 and 9 V...
We found this circuit in an old Popular Electronics. The circuit is experimental, driving an LED...