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.
The frequency depends on the coil and is not found in the original documentation but should be...
This is a device for those who need to show that they know how to use digital electronics but have...
Using an operational amplifier with FET, this circuit from a 1977 publication can generate...