Here is a simple but useful switch circuit that will activate a relay when light falls below a particular level. The sensitivity of the light level circuit can be adjusted by VR1 and the relay contacts that may used to drive an external light or buzzer.
The ORP12 photocell works as a light sensor in the circuit. The dark resistance of ORP12 will high as 1M and in light it will be as low as 80 ohm. The 1M preset will give you a selection capability of light sensitiveness to the dark activated switch. The op-amp senses the voltage difference between pins 2 and 3. The control VR1 is adjusted so that the relay is off, the output of the op-amp will be around 2 Volts. When light falls the resistance of the photo cell increases and the difference in input voltage is amplified by the opamp. This cause an increase in the base voltage of the transistor which results in activating the relay and switching action will takes place.
The ORP12 photocell works as a light sensor in the circuit. The dark resistance of ORP12 will high as 1M and in light it will be as low as 80 ohm. The 1M preset will give you a selection capability of light sensitiveness to the dark activated switch. The op-amp senses the voltage difference between pins 2 and 3. The control VR1 is adjusted so that the relay is off, the output of the op-amp will be around 2 Volts. When light falls the resistance of the photo cell increases and the difference in input voltage is amplified by the opamp. This cause an increase in the base voltage of the transistor which results in activating the relay and switching action will takes place.
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You can assemble the circuit on a general purpose PCB and make sure that the relay contacts provide adequate isolation and have ample rating for the load.
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1 comments:
please i want you to send me the steps on how to design a dark activated switch and the circuit diagram
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