While returning home on a cold winter night it can be really frustrating if one is unable to unlock the gate due to insufficient light. A simple, economic yet reliable solution to the problem is provided by the circuit “Automatic Gate Light”. When it is quite dark, a slightly pressure on the bell switches the gate lights on for a preset interval of time. The circuit automatic gate light is also a valuable addition to domestic security arrangements as it deters unwelcome caller.
Circuit Description of Automatic Gate Light
N1 and N2 if IC1 (CD4011) are wired as inverter gates. When light falls on the LDR, its resistance becomes low, so the output level of N1 at pin 3 becomes high whereas output level of gate N2 at pin 4 becomes low.
VR1 is set so as to switch on the gate light. Switch SW1 is pressed when the light falling on the LDR is very low (at night). VR2 is set for about 0.25V at pin 4 of IC2 when light falls on the LDR and about 0.45V when no light falls on the LDR. Gate light is switched on as soon as switch SW1 is pressed provided no light falls on the LDR. And it remains on for a preset interval of time, which is set with VR3. Gate N3 is also wired as an inverter gate. Its output is high for the time in which SW1 is pressed. Transistor T1 operates relay RL1 which in turn operates the bell. Operation of bell is independent of the light falling on the LDR, i.e. it can be operated both in day and at night whereas the gate light operates only at night.