Introduction: Non Soldering Solar Lantern

About: I used to teach middle school science, but now I run my own online educational science website. I spend my days designing new projects for students and Makers to put together.

Outdoor solar lighting has become extremely popular in the past few years, yet how many people do you know that can explain how it works? Luckily solar is a super simple power source which we can use alongside some simple electrical tricks to make a fun project. This non soldering version is perfect for anyone new to electronics, and is a great project for parents to do with their children.

In this guide I'll be showing you how to create a simple non-soldering Solar Lantern project that can do the following electrical tricks:

Solar Charging

Dark Detecting

Voltage Boosting

While I will be showing you some really fun laser cut designs which you can freely use, I'll also be showing you how to do this same project with a $1 Mason Jar. If the $1 Mason Jar is not your style, a hole punched tin can works wonders as does some well cut heavy card stock. (We'll leave the creativity up to you on this one.)

Step 1: Parts Needed

Many of these parts can be found at a local Radio Shack, but they're going to over charge you on them. We at Brown Dog Gadgets have kit versions of this project available for both the electronics only or the electronics with a laser cut box included.


Wire Stripper

Small Screw Driver Set


Double Sided Foam Tape or Hot Glue

Electronics Parts Needed:

Mini Breadboard

2 Breadboard Screw Terminals

1N914 Diode

2N3904 Transistor

2N3906 Transistor

4.7K Ohm Resistor

1K Ohm Resistor

10mm Diffused LED - (Any color, and you can use more than one.)

Solar Cell rated 4V or Greater

2 AAA Battery Holder

2 AAA Batteries


2 Feet of Solid Core Wire in Red

2 Feet of Solid Core Wire in Black

Options for Enclosure:

Mason Jar

Laser Cut Box (Available for Download)

Step 2: How It Works

We're pretty much making the exact same circuit as found inside your average outdoor garden light. If you can find a cheap one, or a broken one, take it apart and look inside. They're rather simple.

In our project we're really got three different circuits happening at once.

Solar Charging

The first is the Solar Charging aspect of our circuit. This is made up of the solar cell, diode, and battery pack. The solar cell is creating power during the day, the batteries are storing the power, and the diode is preventing power from flowing in the wrong direction. Solar cells have a nasty habit of trying to suck power back into themselves at night, which in turns destroys the solar cell.

In fact, this simple circuit is all you need to make a solar powered AA charger during the next zombie invasion.

Dark Detecting:

Since we don't want our lights to be on during the day, wasting precious energy, we need to assemble a simple circuit that detects darkness. In this situation we're using the solar cell as our "sensor", a 4.7K Ohm Resistor, and a 2N3906 Transistor to control it all.

In a nutshell, the transistor works like a gate. When Voltage from the solar cell is high, the gate is pulled shut preventing energy from flowing through it to the rest of the circuit. As the Voltage drops the gate opens to allow more and more energy through. The resistor is there to adjust the sensitivity of the gate. If you wanted to change how sensitive the dark detecting is you can swap out the resistor for a larger or smaller one.

Voltage Boosting

Voltage is like water pressure. Imagine you have a hose and you're trying to push a ball around with it. Too much pressure and things get out of control. Too little pressure and the ball won't move at all. Like most things in life the conditions have to within a certain range to work properly.

In this situation our "ball" is really the LED. We've got to have enough pressure pushing on the LED to light it up. Unfortunately our two rechargeable AAAs only give us 2.4V of power, and a white LED needs 3.6V of power. Granted, we could just use a larger solar cell and 3 AAA batteries, but we can easily make our own power transformer and boost the voltage up.

To do this we need an iron toroid, two lengths of solid core wire, a 3N2904 Transistor, a 1K Ohm Resistor, and an LED or two.

As you'll see in the following steps we'll be wrapping our wires around the toroid. As you might know, when electricity moves through wire it create magnetism, and wrapping wires around an iron core turns the iron into a magnet (which is how we can create super strong electromagnets!). When this happen around our toroid we end up with a strong magnetic field inside the center of the toroid, which in and of itself is kind of useless. That is until we bring our second transistor into the mix. The 3N2904 transistor is turning this magnetic field on and of over one thousand times a second causing our magnetic field to be created and then destroyed over and over again.

When the field is destroyed the magnetic energy has to go somewhere and the easiest place to go is back into the wires around the toroid. Through this process we end up boosting up the Voltage. In fact if we wanted to we could power a great many LEDs through this simple circuit. Going back to our water analogy, it would be similar to you putting your finger over the end of a hose to change the pressure coming out, giving you more power.

With the voltage boosted up the LED can now turn on... and off... 1000 times a second. Though to our eyes it looks continuous. It's exactly the same process that movies and TV use to trick our brains into turning 30 pictures per second into continuous movement, or bored students use to create flip book animations on the corners of their notebooks.

The only downside to this process is that in exchange for the increased Voltage we end up wasting Amperage. If Voltage is water pressure, Amperage is the amount of water you have in reserve. Also, this process doesn't work with all types of LEDs. Specialized natural color changing LEDs won't work since they require a constant stream of energy to do their fancy color changing.

Step 3: Video Directions

In case you're more of a video person, here is a step by step guide to wiring it all up.

Notice how even I mess up at one point. Thank goodness I'm using a breadboard.

Step 4: How a Breadboard Works

Back in the old days of electronics, people would build their projects onto pieces of wood in order to hold everything down. Frequently they'd use actual breadboards as they were flat, smooth, and readily available.

Our modern day Breadboards are very handy tools for prototyping projects and a whole lot easier to use.

Breadboards work by connecting components that are side by side together. Inside every Breadboard are long parallel strips of copper. If you plug five items together in Row 1, it would be the same as if you soldered them all together. All the holes in Row 1 are independent from all the pins in Row 2, and so on.

The joy of using a breadboard is the fact that if you screw up, or want to change something, or really really really screw up, all you need to do is unplug your parts. No harm, no foul.

One of the best visual representations I've seen as been from the Arduino-Info Wikispace. In the above diagram you can see which holes are shared, and which ones are not shared. A breadboard is an inexpensive "must have" for anyone doing electrical projects.

I'm using a very small breadboard in this project which only has horizontal strips, and lack the long vertical "power bus" strips found on larger breadboard. Mine also lacks numbers or letters on it.

Hidden Breadboard Fact: All mini breadboards and most other breadboards have double sided foam tape on the bottom. This means that you can peel off the bottom protective layer and stick it to any surface. Though once it's on it isn't going anywhere. We'll be doing just that in our project.

Step 5: Prepare the Parts

Before we start you'll need to make sure a couple parts are properly prepared.

Your solar cell needs to have wire attached to it. Yes, that may seem obvious, but it's kind of important. Our kit version comes prepared that way. You can also buy solar cells with wires attached to them.

Same with your 2 AAA battery holder.

You can do the same to the long solid core wires, but you probably should just wait on that.

Step 6: Dark Detecting Circuit

First, grab one of the screw terminals. Screw the Positive wire from the Solar Cell into the right hole, and the Positive wire from the Battery Holder into the left hole. Which hole we use does make a difference.

The Breadboard is divide into two halves, and we'll only be using one half. My Breadboard is also not numbered, but I'll be giving you rows if yours is. If yours isn't numbered, well, just count them down since we're not doing a lot. If you're confused, scroll down a bit and you'll find a row by row breakdown of everything.

Put the Screw Terminal into the top left two slits of your Breadboard. If the rows are numbered, this would be row 1 and 2. Notice how I have it facing "backwards" so that the wires are going away from me.

Grab your Transistor. You want the 3N2906 Transistor. With the transistor facing you, bend the left leg out a bit.

Put the left leg in the second row, in the first hole not taken up by the terminal block. The middle leg should skip a row (Row 3) and into Row 4. The final leg, the far right leg, can go in the next row which would be Row 5.

Grab your Diode. Notice how one side has a black line on it. That is the Negative side.

Put the Positive side of the diode into the first row, in the first available hole not blocked by the terminal. The Negative side will go to the second row.

Grab your 4.7k Ohm Resistor. It does not have a Positive or Negative side.

Put one end of your Resistor in Row 1, and the other end in Row 4. Row 4 is the middle leg of your Transistor.

If you feel the urge to you can cut the legs of your Diode and Resistor down some in order to get them to sit more flush with the Breadboard.

By Row

Row 1: Solar Cell, Positive side of Diode, 4.7k Ohm Resistor

Row 2: Battery Pack, Negative Side of Diode, left leg of transistor

Row 3: Nothing

Row 4: Middle leg of transistor, 4.7K Ohm Resistor

Row 5: Right leg of transistor

In the future, Row 5 will have two bits of our solid core wire going into it, but not now.

Step 7: Winding the Toroid

If you're going to mess up, this is where it's going to be. Pay careful attention to how you wrap your wires, and which wires to choose.

Grab your two lengths of solid core wire. They should be around two feet in length.

Put the about 3 inches through the Toroid.

Now start wrapping the two wires around the Toroid. You want them tight.

Its extremely important that your two wires are always parallel with each other. Meaning that they don't cross or overlap at any point. In my case I'm paying close attention to make sure that they're always going RED BLACK RED BLACK RED BLACK.

Again, overlapping is bad. Twisting is bad. Crossing is bad.

You want at least 8 wire loops by the time you come around.

Give yourself about 3 inches of wire at the end, then cut, then strip all the wires.

Now you've got two wires, two colors, and four ends.

Lets call the Side A and Side B. This means we have Red A, Black A as well as Red B, Black B.

Take Red A and Black B and twist the wires together. These two wires are the ones that go into Row 5 with our first transistor.

Black A and Red B are needed in the next section.

Step 8: Voltage Boosting

In this part we'll be thinking "right to left" on the breadboard. This means that the furthest right row is now "Row 1" in this section.

Take the Negative wire from the Battery Pack and the Negative wire from the solar cell and twist them together.

Screw them into the right side of the second Screw Terminal.

Put that Screw Terminal in the top most right side of your Breadboard. Going from right to left, this means Row 1 is empty and Row 2 has the two Negative Wires.

Grab your Transistor. This is the 3N2904 Transistor.

With the transistor facing you, put the right leg in Row 2, which is the same as the Negative wires. The middle leg is in Row 3 and the left leg is in Row 4.

Grab your 1K Ohm Resistor. Put one of it's legs in Row 3, which is the same as the middle leg of the transistor. Place the other leg somewhere to the left in the middle of the breadboard. It doesn't matter where.

Grab your LED. Notice how it has two legs. One leg is long, one is short. The long leg is Positive and the short leg is Negative.

Put the Negative leg in Row 2, which is also the same row as the right leg of the Transistor and the Negative Wires.

Put the Positive leg in Row 4, which is the same as the left leg of the Transistor.

Take a deep breath. Grab your Toroid.

The two wires you twisted together, put them both on the "Dark Detecting" side of your Breadboard. They will go with the first transistor's far right leg.

Now you have two leftover wires. Take one (it doesn't matter which) and put it in the same row as the Positive Leg of your LED. (From right to left, this is Row 4)

Take the final Toroid wire and put it in the same row as the unused leg of your 1K Ohm resistor. In my pictures this is in the middle of my board away from everywhere else.

By Row - Right to Left

Row 1: Empty - Unused pin of the Screw Terminal

Row 2: Negative Wires of the Solar Cell & Battery Pack, right leg of the transistor, Negative leg of the LED.

Row 3: Middle Transistor Leg, One side of the 1K Ohm Resistor

Row 4: Left leg of the Transistor, Positive leg of the LED, one of the two "free" Toroid wires.

Middle of nowhere: Other leg of the 1K Ohm Resistor, now of the two "free" toroid Wires.

Step 9: What Can Go Wrong

Put your batteries in. Put your hand over the solar cell, or have it face down, and your LED should light up. At this point you can grab your enclosure and put the Battery Holder and Breadboard on the inside top over, and the solar cell on the top.

That is, if it's all working.

Common mistakes:

1) You've gotten your Transistors mixed up, or they're facing backwards.

2) You've got your LED in backwards. Long leg is Positive.

3) You have overlap issues with your Toroid. Undo the wires, try again.

4) The solar cell or battery pack wires are mixed up.

5) You're off a row. Somewhere. Make sure everything is lined up properly. It's easy to accidentally put a leg in the wrong hole.

6) Something isn't pushed in. Usually this is with the Toroid wires.

7) Is your solar cell facing up? If so it's reading "daylight", so just put your hand over it.

Step 10: Easy Enclosures

We have a few easy and inexpensive suggestions for enclosures.

Easy: Mason Jar. Wide mouthed, otherwise things don't fit inside. Attach everything via foam tape.

For extra fun paint the jar, cover it with glue and roll it in colored salts, sand blast it, etch it, or fill it with colored glass.

Easy: Tin Can

Poke holes in ti and use it to make stars on the wall. A coffee can works best.

Easy: Pumpkin

Is it Halloween? Light up your pumpkin. Use two LEDs, attach some long wires to them, and give your Pumpkin two LEDs eyes. Solar Pumpkin? Oh yes.

Step 11: Laser Enclosures

We really love making our Lanterns using laser cut designs. If you have ANY experience with graphic design you can create your own stencil in no time.

If you're not good at graphic design, well, just download one of our very nerdy designs. I suggest the Globe design in conjunction with a Blue LED.

These files are set up for 1/8th inch wood. We use either Baltic Birch or Acrylic. For the diffusion panels you can use paper, though in our kits we use a different thin piece of laser cut plastic.

If you'd like to get really fancy you can paint or wood stain your box. A little bit of spray paint makes them looks nice, a bit of wood stain makes them look classy.

To make your wooden/ acrylic lantern box you'll need some glue, some foam tape, and some rubber bands.

First, use the foam tape to tape the diffusion panels into place. You'll want to do this on the "inner" side of the four sides. With a laser cutter this typically means the side with the scorch marks on it. (Which is why this is the inside so we can't see it.)

Next, grab two sides. Make sure they fit together. Grab your glue and put small dots along the side where they meet. Test this out first to make sure you've lined everything up.

Once two sides are done, put glue on a third side. Then a forth.

Then add the bottom. It helps to have your box upside down so that gravity holds the bottom in place.

DO NOT glue the top on, but for stability it helps to put the top on.

Once everything is glued, and you've most likely got glue all over yourself, use rubber bands clamp it all together. If you have clamps, use those. Be sure to use a paper towel to dab away any excess glue that has poked out.

Wait for an hour or so for it all to dry.

Once dry, put your solar cell on top, and the Breadboard and Battery Holder on the inside. The breadboard does have a foam tape bottom for easy securing it to the lid. The Battery Holder will need a small amount of tape.

Step 12: What About Soldering?

Yes, you could easily freehand solder this! Or just grab the PCB version that I've also got available. Same thing, just with an easy to solder PCB.

I'm not a big fan of freehand soldering this project. The transistors tend to get their legs broken frequently.

If you were very adventurous you could use two terminal blocks to screw everything into place, provided the transistor legs stretched that far. I've done it once, but it was quite annoying.

Step 13: Display and Enjoy

At this point you're enjoying a very pretty lantern, or cursing the heavens because it doesn't work or because you're all covered in glue. Either way you probably had fun.

Feel free to use the laser cut designs we've provided for your own noncommercial use.

The lights on these guys should run all night after a decent day's sun. Our Kit version uses a 6V 80mA solar cell, which means we should get around 400mA of power out of a day's sun (assuming five hours of decent light).

Of which, you should really grab one of our Kits. We have both a Soldering and Non Soldering version, and versions that come with Laser Cut boxes if you need one.

One nice thing about the Breadboard version is that it's very simple to swap out LEDs. Halloween? Red LED. St. Patricks Day? Green LED. Mood lighting for a romantic evening? Blue LED. Looking to annoy people? Yellow LED.


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