The reference voltage for this circuit can be selected digitally. The circuit is from Radio Electronics dated February 1981. The 741 must be powered by a symmetrical source.
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...