Light Controlled Blinker

This project is a very slow blinker (oscillator) with a frequency of one cycle every few seconds (depending on the amount of light present). The CdS cell controls the charge and discharge rate of the 100uF Capacitor and this controls the ON/OFF time of the 2SA(2) Transistor. This, in turn, controls the ON/OFF time of the 2SA(1) Transistor.

When it is ON, the 2SA(1) supplies current to energizes the Relay coil. This completes a path for electricity from the 3V Battery to flow to the Lamp and turn it ON.

When the 2SA(1) is OF, the Relay coil is de-energized and the Relay contacts return to their other position.

At first you may think the Lamp should be ON all the time, because of the current from the 9V Battery. However, if you look closely you will see that the Diode is biased against the the current from the 9V Battery and will not let it flow to the Lamp. You will find that this project works best without the CdS Cell, unless you are in extremely bright light.

You may want to try replacing the 100uF Capacitor with the 10uF, for a faster rate of blinking.