Found in a Popular Electronics from the 90s, this circuit uses common components with several operational options, including the use of an optocoupler that allows its application in a shield.
With the configuration shown in the figure, a common 12 V lamp lights up when light no longer...
This circuit was obtained in documentation on medical applications from 1966. The circuit is used in...
We found this circuit in an Australian publication from 1991. The circuit has good sensitivity, presenting...