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Solar Charging Night Light

Instructables Electronics Project

Like so many electronics projects in my life, I got this idea while randomly walking around Hobby Lobby. I came across these cute little glass "light bulbs." They have screw off tops, a flat bottom, and only cost $1.50. Who could pass that up? My original idea was to try to cram a LED, battery and switch in there. Yeah, that wasn't ever going to happen. My second idea was to make it solar powered because as we all know, everything is better with solar. (Yes, even puppies!) In a nutshell what I ended up making was a little side box that had a solar panel, Joule Thief circuit and a switch on it connected to the glass bulb. Oh yeah... I threw in a simple dark detecting circuit as well. Just cuz. This is a fun beginners project for anyone wanting to do some soldering. I have other light detecting solar circuit kits on my gadget website, Brown Dog Gadgets.

Required Tools:
Hot Glue Gun
Soldering Iron

Parts List:
Breadboard (optional, but super handy.)
22 Gauge Wire
Magnet Wire
5KΩ resistor
1KΩ resistor
1 Zener diode
3 White LEDs
PNP transistor
NPN transistor
Toggle switch
4.5V solar panel
AAA battery holder
AAA NiMh battery (you can also use AA)
Glass Lightbulb
Little Plastic Bead Box

Tools You Will NeedTools You Will Need

Gauge WireGauge Wires

Battery HolderBattery Holders

Light BulbLight Bulb

Step 1: Making the Circuit

In addition to making the circuit (borrowed from evilmadscientist.com) I'm am also adding a switch between the LED and the battery. This will allow the battery to charge even if the switch is off.

The first transistor PNP 2N3906 acts as a dark detector. When power (sunlight) is hitting the solar panel, the transistor is off. When there is power (darkness) coming from the solar panel the pathway turns on and we get power.

If you decide, you can skip this step and control the LEDs via the switch. After the first transistor we get the famous Joule Thief Circuit.

Schematic Switch Placement
Schematic Switch Placement

Step 2: Wire Up The Solar Panel

Solder on wires as shown in the images below. When you're done, put some tape over the tabs – they break easily.

Panel and Wire Panel and Wire

Tape the Tabs Tape the Tabs

Step 3: Wrap Your Toroid

Wrap your toroid up with wire. Use two wires, coated of equal lengths. Wrap the wire around the toroid at least seven times. Lastly, take a wire from one "end" and hook it up with the opposite color from the other end.

Wrapped ToroidWrapped Toroid

Connected WiresConnected Wires

Step 4: Breadboard Testing

It is highly recommend to use the breadboard to test everything out.

Image A: The LED is off because the solar panel is getting light.
Image B: I covered the panel and the light goes on. Darkness detected!

Breaboard Testing Image A: Breaboard Testing

Led turns on by covering solar panel Image B: Led Turns On by Covering Solar Panel

Step 5: Drill Baby Drill

Drill three holes in the bead or plastic box. I placed one in front for the solar panel wires, one on top for the switch and one out the back for the LED wires. The size is up to you and depends on how big of a switch you're using.

Drill holes in plastic boxDrill Holes in Plastic Box

Step 6: Soldering the Dark Detecting

If you're not going to be working on the dark detecting section, you can skip this section. Otherwise, read on!

First, don't forget to thread your solar panel wires through the hole first. Now solder the zener diode and the 5kΩ ohm resistor to the positive wire. Solder the resistor to the center leg (base) of the PNP transistor. Then solder the zener diode, as well as the positive side of the battery case, to the left leg (emitter) of the transistor. Solder the double twisted end of the toroid to the right leg (collector) of the transistor.

Solder connectionsSolder Connections

Back side of the transistorBack Side of the Transistor

Attaching the toroidAttaching the Toroid

Step 7: Test the Connections Again

Use the breadboard and test everything again. It never hurts.

Breadboard testingBreadboard Testing

Step 8: Diffuse Your LEDs

If you're smart, you would be using diffused LEDs. If you only have clear LEDs, you'll have to diffuse them first. To do this you can either use a big ball of hot glue to cover the lens or use sandpaper to scuff it up.

Clear LEDsClear LEDs

Diffused LEDsDiffused LEDs

Step 9: Joule Thief

Off of the toroid are two wires. Take one (doesn't matter which) and solder the 1KΩ resistor to it. Now solder the other end of the resistor to the middle leg (base) of your NPN transistor. Solder the other toroid wire onto the right leg (collector) of your NPN. The Joule Thief is nearly finished.

Joule ThiefJoule Thief

Step 10: LED Connection

I used long pieces of thick magnet wire because of the look and I wanted to hide the box away from the bulb. Anything will do, provided it fits through the hole in the bulb cap. First step is to put the wires through the bulb cap. (You can always make it bigger by using your drill). Then hook up all positive legs of your LED to one wire and all negative to another.

Note: If you're using a 8mm or 10mm LED, you might want to start with two and see if they'll fit into the bulb. Then, maybe add a third while the other two are inside the bulb. It's just like working on a ship in a bottle.

LED ConnectionLED Connection

Step 11: Hook Up the Wires in the Box

Take the other end of your LED wires and put them through the hole in the box. Solder the positive one to the far right NPN leg (collector) (the one you already soldered the toroid wire onto).Then run another wire off the switch. Last, solder the new wire off the switch, the negative battery wire and the negative solar wire all to the left leg (emitter) of the NPN transistor. Now you're done soldering.

Positive Wire ConnectionPositive Wire

Negative Wire ConnectionNegative Wire

Solder Final Wires Negative LED Wire, Battery Wire and Solar Wire Soldered

Hot Glue Gun Getting Ready to "Goo"

Step 12: Warm Liquid Glue or Should We Say "GOO Phase"

Now we have a big mess of wires and stuff that needs to go into the box, and we want to make sure to avoid the possibility of a random exposed wire touching random exposed wires.

Hot glue powers activate!

Covering all the random exposed bits with hot glue makes things much easier. Word on the street is that the technical term for this is "potting."

Hot Glue GunGetting ready to "Goo"

Cover exposed wires with glueHelp me I'm Melting

Step 13: Shove It All in the Box

Be careful to shove everything into the plastic box. Again BE CAREFUL. Breaking something now would be a big pain to fix.

Component CaseEnclosed Case

Step 14: Enjoy!

You have now created what amounts to a very fancy looking outdoor solar light, the kind you can buy for less than $5. Only this one looks very impressive and was built by you. This is a great project for those interested in a beginner's circuitry project and is inexpensive to make.

To really impress your friends, use two colors of lights inside the bulb that you control using a second toggle. Go from the NPN to a toggle switch with two positive lines running out. Use a common negative line back. You'll have three wires instead of two.

LED Light BulbCompleted LED Light Bulb

View complete project instructions here.