I made a circuit for automatic night lamp using LM358 ic and photodiode which cost less than $1.

Step 1: Gather the Components

1 x photodiode

1 x 10k ohm resistor

1 x 10k preset

1 x 5v SPDT relay

1 x LM358 IC with 8 pin ic base

few wires

and soldering iron

Step 2: Place the Compponents

Place the components according to circuit diagram I've given above

Keep in mind that photodiode has to be placed in reverse bias direction. Reverse bias means cathode of photodiode connected to positive wire coming from power supply and anode connected to 10k resistor.

Reason behind connecting photodiode in reverse bias direction is ,photodiode is more sensitive to IR rays in reverse bias direction than forward bias and gives more resistance when not engage with IR rays.

Pin 3 of IC base is connected to junction where photodiode and 10k resistor is connected

and pin 2 of IC base is connected to middle pin of 10k preset (variable resistor).

Output is obtained at pin1 of IC base

Step 3: Connection of Relay

Relay has two pin for coil and has NO,NC and common pins.

Output coming from IC is connectd to one of pin of coil and other pin of coil is connected to ground.

whatever appliances you want to run on relay or gadgets should be connected to COM and NC pin of relayin series combination . Means if you want to connect your night lamp to relay, just cut a signle wire coming from AC supply to night lamp.

Now your night lamp is coonected to AC supply by only one wire and another has cut off by you.

Now take the end of cut wire of night lamp and solder to NO pin of relay and end of cut wire coming from AC supply solder to COM pin of relay.

Step 4: Working

During daytime,sun emmits sun rays with IR rays which detected by circuit so it gives signal to LM358 IC which amplify the signal and gives enough voltage to relay to actuate.

So that connection NO pin becomes NC, and therefore your night lamp is not working.

AS sunsets,IR rays in atmosphere goes low and so photodiode does not send any signal to LM358 and hence whole circuit is not working except relay, NC pin activates and completes circuit between AC supply and night lamp , and so your night lamp glows !!!

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