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Light sensitive switch circuit design electronic project

This light sensitive switch circuit is designed using common electronic parts and can be used in applications like scale automatically lighting, automatically opening a door under the action of a beam of light .
This light sensitive switch circuit uses photo detection method , with an element placed in a bridge circuit and a comparator is used as a detector of "balanced bridge". Comparators output order a thyristor through a transistor. For this circuit, protective measures must be taken because it is not insulated from photoresist (LDR). IC1 is used in comparator configuration and the voltage will be approximately 1.8 V when the potential at the inverting input (negative) will surpass voltage of the noninverting input. Resistance R5 creates a hysteresis of about 1 V to prevent T1 and thyristor to oscillate at the limit of light. Tipping point of the comparator can be adjusted from P1. With the potentiometer set to minimum (minimum resistance) lamp will be lit at twilight. If you want more flexibility, replace P1 with one that has a value of 1Mohm. If you want a reverse operation, the position in the scheme of photoresistor can be changed with the P1/R4 group. LA1 lamp goes out, in this case, at the dark.
Maximum gate current is 250 uA Th1, which means you need to use a very sensitive thyristor.

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Light sensitive switch circuit design electronic project