We found this circuit in the Radio Electronics magazine of February 1993. The main integrated circuit is from that time and the power supply is made with voltages of 6 to 15 V.
This photometer is based on a Wheatstone bridge that must be balanced by the linear potentiometer P1. The...
This circuit also appears elsewhere on this site, obtained from other sources. This is an 80's...
This circuit is from a 90s Popular Electronics. The circuit employs a ZN461E that is not a common...