Let's learn how to build dark activated LED lights to brighten up the dark time of the year.
It's winter, it's cold, and it's dark outside. What's better than bringing some light into this darkness. In this year's DIY project, we are going to build our own dark activated LED lights from a cheap battery operated LED string.
Here is what we need:
Additionally, you are going to need to following tools:
Let's have a look at the circuit for this project. The LEDs shall light up when it gets dark outside. We can achieve this by using a simple transistor circuit which is shown below.
The LDR and the resistor R1 form a voltage divider. The resistance of the LDR increases the darker it gets. A high resistance of the LDR means a higher voltage at the MOSFETs gate. As soon as the gate voltage crosses the 1 V mark the MOSFET starts to turn on.
To control at which brightness level that happens we can tune the value for resistor R1. The optimal value depends on how you want to use your LED string. If it you want it to only turn on, if it is fully dark you require a high value like 470 kΩ or more. If you want it to also light up on darker days, you need a lower value like 10 kΩ.
I can only encourage you to experiment, until you find the value that fits your use case. If you don't feel like experimenting, I can recommend you to use 100 kΩ. It should fit for most indoor use cases.
Step 1: Let's go! As a first step, we place the components on the perfboard without soldering them in yet. If you want to, you can already cut them to the right length.
Step 2: With the components in place, we can use a pencil to mark the positions in which we want to drill the holes for the wires.
Step 3: For drilling, we need to remove the components again and make sure to safely clamp the perfboard on a piece of scrap wood. We can then drill the two holes.
Step 4: With the holes made, we can now place the components to finally solder them in.
Step 5: After that, we connect the resistor and the LDR to the MOSFETs gate with a solder bridge.
Step 6: Next, we need to attach our LED string and its battery holder. For this, cut its wire in half and tin the ends of each side.
Step 7: Pull the wire through the holes and fixate them in place with a knot. The knot serves as a strain relieve.
Step 8: Now for the tricky part: Take a multimeter and determine the correct polarity of the LED string and the battery holder. Connect the positive side of the LED string and the battery holder directly together (+). Connect the negative side of the string to the MOSFETs drain (D) and the negative terminal of the battery (-) to its source pin (S).
Step 9: As a final step, use some wire or the cutoffs of the components to connect the LDR to the negative and the resistor to the positive side of the battery.
Finished: It's done! If you turn on the battery and cover the LDR, the LEDs should now light up. In light, they should turn off again.
And there it is. Using our little circuit, we now have made our own dark activated LED lights. May they be of joy to you!
Have a merry Christmas and a happy new year. Be blessed!