This 1964 Electronic Design circuit uses a photo-FET as a sensor. The component is rare today.
This circuit was obtained from a 90s Radio Electronics. The value of R1 determines the scale...
This circuit is from 1992 documentation, but it can still be assembled today, as the components used are...
This circuit is from the Motorola Linear Databook of 1990. The values of the components depend on the...