Introduction: Automatic Light System

About: Hi, I am 17 years old and I love making new things and learn something new along the way, so E-Mail me at:

Lights are essentials in every home, and when your guests arrive you have to turn them on, right? But lights are wasteful, they take so much energy, so I have come up with this design to help you turn the lights for the guests and save energy.

And if you are annoyed about hooking it up to an electric outlet, no problem it has a built in solar panel to power it along with 4 AA rechargeable, and the best part is that it costs roughly 10 $!!!

Please look at the schematic, understand it and then make it, this is not an easy build so be careful, you will learn also a lot about electronics.

But how does it work? Simple. the first LDR detects if it is day or night and the second LDR detects motion from people, so if it's day and there is someone detected by LDR it will not turn on because it's day, but if there is someone and it is at night it will light up.

Please vote for it in the contests.

Step 1: The Schemtic

Look at the schematic and understand it.


1. It doesn't matter if you have a 1 mega ohm resistor in Dark, all you have to do is change the transistor from PNP to NPN.

2. R2 is important and varies from one circuit to another, so experiment or use a variable resistor.

3. L1 and W1 are a relay, a 5V Normally Open Relay.

4. The motion detector is 1$ Electronic Guest Saluting Doorbell.

5. C3 is for protecting the transistor from a shock when the power is out.

6. R3 is for protecting C3 from a shock when there is no shock.

7. You can get the parts abo

Step 2: Materials and Tools

For this project you will need:

These Parts:

1. 6V solar panel.

2. Motion Sensor from the dollar store.

3. 5V Normally Open Relay.

4. LDR 1M Light/Dark.

5. Transistors (Mainly NPN)

6. 7805 5V Voltage Regulator.

7. 1000uF Capacitor.

8. 100nF Capacitor × 2.

9. 1uF capacitor.

10. 1N4001 Diode × 2.

11. Resistor.

And these tools:

1. Soldering Iron.

2. Solder.

Step 3: Breadboard Your Parts

You can check your components by using a breadboard.

Step 4: PCB: Daylight Switch + Regulator

This step is pretty complicated so I have put images to show it in detail, here are the steps:

1. Split the PCB in half or cut it.

2. Add two wires to represent the positive and negative supply lines.

3. Add the transistors, I recommend using the 2N3906 PNP transistor if you have a 1M LDR in light, or the 2N3904 NPN transistor for 1M LDR in dark, just pay attention to the polarity, from left to right the pins are (Emitter, Base, Collector) for both transistors, if you are using the PNP put the Emitter to the positive supply line, if you are using the NPN connect the Collector to the positive supply line.

4. Add the LDR (It doesn't have a polarity).

5. Add R2, R3,C3 (from the schematic), put one end to the transistor's base and the other to the negative supply line.

6. Add the regulator with it's capacitors as shown in the schematic, paying attention to the polarity.

7. Open the device, since it only has a battery pack of 3 we will attach another one, and since it has a maximum voltage of 4.5 we are going to use 2 diodes to reduce the voltage.

8. Connect the output of the transistor to the positive supply line of the device after you connect the battery.

Step 5: PCB: Relay Module

To the other PCB add add the NPN transistor with the relay, the diode, the 1000uF capacitor and a 1 Ohm resistor, then remove the speaker wires identify the positive from the negative, then connect the positive to the base of the transistor and the negative to ground,

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