Description.
Many automatic night light circuits had been published here. This one
uses a photocell for detecting the light intensity. At full light the
resistance of the photocell will be few ten ohms and at darkness it will
rise to several hundred ohms. The IC1 uA741 is wired as a comparator
here. At darkness the resistance of photocell increases and so the
voltage at the inverting input of the IC1 will be less than the
reference voltage at the non inverting input. The output of the IC1 goes
to positive saturation and it switches ON the transistor to activate
the relay. By this way the lamp connected through the relay contact
glows. The diode D1 works as a freewheeling diode.
Circuit diagram.
Notes.
- The circuit can be assembled on a Vero board.
- Use 9V DC for powering the circuit.
- POT R7 can be used to adjust the sensitivity of the circuit.
- The relay K1 can be a 9V, 200 Ohm SPDT type.
- L1 can be a 230V,60W lamp.
- R8 can be a ORP 12 photocell.
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