The configuration shown was found in an old Poptronics but can be easily assembled using a common calculator photocell. The relay is according to the supply voltage.
This passive tuned circuit was found in a 90s Popular Electronics. The coils must be according to the...
This circuit is suggested by Motorola and is based on the well-known 723, integrated voltage...
This circuit appears in other versions in this same section of the website and in other sections with...