This circuit was found in a Hands On Electronics from the 80's. The circuit emits an audible alert when dawn and the sensor receives solar illumination.
This circuit uses a 100 kHz crystal, but nearby frequencies can be obtained with appropriate...
The component used in this circuit that we found in an old documentation, is not easy to obtain...
This oscillator uses germanium transistor avaialble in 1958 when the project was published....