Introduction: LedUSB : Converting Solar Energy Into Electrical Energy With the Use of LEDs

Yes you read it right.

Today we are going to make a LED matrix that generates free energy enough to charge your phones and tablets.It is a portable handheld device that can charge a device. We had the main concern on that it should be portable , lightweight and cheap.This LED matrix can be made very cheaply as 100 Red LEDs cost only $2 on . We have used a joule thief circuit with a resistor, a ferrite toroid, a ceramic disk capacitor and a transistor as extra materials that cost you $1.Whereas solar panels that give you 5v are much bigger than this and are expensive ranging between $40 - $100.

So basically we are going to develop a source of infinite energy (till sun remains) which charges your phone for lifetime under $3 and then also it is 1/4 of the size and 1/8 of the cost of same capacity solar panel . A phone battery is charged around 1826 times in its lifetime so if we divide $3 by 1826 so it costs $0.00164293538 to charge a phone one time . Literally, that's what we spend on nothing . So it's a bit cheaper than normal solar panel that cost $0.0273822563 per charge that means 2 cents for every charge.

So now you must have understood that what we are going to do in this project. Literally we are going to Save Energy.

Watch LedUSB Teaser.

Our Main Concept Video.

Step 1: Google Science Fair 2015

This is our contest entry for Google Science Fair 2015.

Please support us by watching,liking and sharing our videos.

Thanks for your support. Each and every view matters.

Step 2: Research

For this project we searched a few sites and we found that very less has been posted about this idea.

Then we found two sites namely and that had some research data.

Through them we inferred the following data-

Working of LED
In any normal PN junction diode, when a recombination occurs, the energy produced at the junction is released in the form of heat. These radiations are invisible. Unlike a PN junction diode, semiconductor materials like GaAsP and GaP are used in case of LED. If these materials are used, then recombination at the junction results in production of photons. Thus, the junction can act as a source of light.In the figure shown below, anode is given a more positive potential than the cathode. This makes P region more positive than the n region. This positive potential at P region repels holes to the n side and the negative potential at the n side repels electrons to the P side. So, holes and electrons recombine at the PN junction and this produces energy. In case of an LED, this energy will be released in form of photons. These photons escape through the window provided on the anode and hence, the LED acts as a light source.

Colours & constructions-

Depending on the type of material used to make the PN junction, the wavelength of light produced varies. Different colours are produced for different materials used in the construction.

Amber - AllnGaP

Blue - GaN

Green - GaP

Yellow - GaAsP

Red - GaAsP

White - GaN

How LED works as a solar cell?

Red LEDs act as solar cells when irradiated by solar energy.When solar light is allowed to fall through the window of an LED, the photons in the light which has wavelength equal to the band gap of LED penetrates deep into the PN junction. On absorbing energy from these photons, the electron hole bond at the PN junction breaks and result in accumulation of electrons in the n side and holes in the p side. So, p side will be more positive than n side. This makes anode positive and cathode negative. Hence, LED acts as a cell.

LED solar panel -

The voltage produced by a single red LED is around 0.7 to 1.3 volts but its output current is very low. So, a single LED cannot be used for powering any device. To increase its output current and voltage, we will use a combination of LEDs which are connected both in parallel and in series. The advantage of this is that the parallel combination increases current rating while the series combination increases voltage rating.If the current output of a single LED is around 100uA, then 2 LEDs in parallel can produce 200uA. Similarly, if the voltage produced by a single LED is around 1.3 volts, then 2LEDs in series can produce 2.6 volts.

Typical applications
1. They can be used to construct cheap solar cells.

2. They can be used for mobile phone charging.

3. They can power double voltage oscillators used for low power devices like mosquito repellents , calculators and digital watches.


1. The cost incurred is low. They are economical in use.

2. They are easily available.


1. If it is exposed to sunlight for long period, the LED can damage. In order to prevent this, high power LEDs can be used.

2. All the LEDs should face the sun at the same angle. This can be done by mounting all the LEDs on a common PCB.

3. Since the output current is low, for high power applications, more number of LEDs must be used but this makes the circuit bulky.

After all this research we made a circuit and tested it

It's Video-

Step 3: Concept

After reading the previous data we started to work on leds like which color provides most energy and which size of the leds is suitable.

After studying all this we have found that red and infrared led work best and 5mm normal leds work best as all sizes of leds give mostly similar outputs.

Then we thought to design a few prototypes and circuits of this idea.

First Prototype:


Design First


Circuit First

We made this prototype first.In this prototype we needed a lot of LEDs and they all should face in same angle. Constructing this we found that it was a big version and needed some changes to make it more reliable and portable.

Second Prototype:


Design Second


Circuit Second

After first prototype we founded some changes and then developed entirely new circuit with minimal LEDs and minimal components. But what if there is no sunlight around? To find this answer we made another prototype.

Third Prototype:


Design Third

This was the final prototype of LedUSB which gave output of 5.2v in minimum sunlight.This circuit is just same as second circuit but we have added rechargeable cells to improve its working. This is the circuit we are going to make in this instructable.

*Hint-Click the images for bigger images. :D

Step 4: Watch the Video

Our Main Concept Video-


Testing the Output Voltages-

Making the Joule Thief-

Step 5: Gather Stuff

For making this project you may need the following stuff-

(4x) 5mm Red Leds$1.99Buy
(1x) Perfboard$2.41Buy
(1x) 1K ohms Resistor$0.29Buy
(2x) Rectifier 1N4007 Diodes$0.20Buy
(1x) 5v or 6v Zener Diode$0.33Buy
(1x) 2N2222 Transistor$0.95Buy
(1x) 16v 100nf Ceramic Disk Capacitor$2.27Buy
(1x) Ferrite Toroid$0.24Buy
(4x) 1.5v Rechargeable Cells$11.99Buy
(2x) 9v Battery Caps$2.99Buy
(1x) USB Port$0.01Buy
Some Wires

*Hint-Click the print button to save a copy of this bill in PDF format. :D

Note-All items rate are in bulk.

Step 6: Scavenging Parts From Old Electronics

In this Instructables we need some common parts so why not scavenge them from old electronics?

Where we can get these things?

  1. LEDs-We can get these from old electric bulbs that may have a maximum of 30 LEDs.
  2. Diodes-We can get upto 9 diodes from a broken CFL.
  3. Capacitors-We can get these also from old CFLs.
  4. Transistors-We Can get these from old R/C cars and stuff.
  5. Resistors-We can get some resistors from old phone chargers.
  6. Toroids-We can also get these from a CFL.
  7. USB Port-We can get this from old pen drives or USB Cables.
  8. Battery Cap-We can get some battery caps by opening a 9v Battery.

Opening a CFL-

Opening A 9v Battery-

Step 7: Tools Needed

For this project you may need these tools-

  1. Soldering Iron
  2. Multimeter
  3. Pliers
  4. Wire Cutter
  5. Hot Glue Gun
  6. Dremel
  7. Super Glue

It's not necessary for you to have these tools so you can get them here.

Let's start working on this project.

Step 8: Making the LED Circuit

Now let's start making the first and very important part of our project that is the LED Matrix.

Just take all four LEDs and solder each two in parallel as shown in the images.

Then solder the two groups in series and take out wires for positive and negative.

Step 9: Winding the Toroid Core

Now just take the ferrite toroid core and two simple wires.

Then start rolling the wires round the ferrite toroid core about 7-8 times.

make sure that the wires are evenly spaced.

Video Tutorial-

Step 10: Making the Joule Thief Circuit

First of all, place all the six components including the ferrite toroid on the perfboard. Make sure that everything fits perfectly on the perfboard and the perfboard should be of dimensions 2*3.5 = 7cm².

Then turn the perfboard and solder all the components as shown in images.

This completes the joule thief circuit.


Joule Thief Circuit

Video Tutorial-

Step 11: Completing Circuit

Now take the LED matrix and solder its positive and negitive terminals to the joule thief circuit input.

And now take the USB port and solder it to the output of the joule thief as shown in images.

Now take a battery cap and solder it with a rectifier diode and then solder it to the USB port as shown in the circuit.

Step 12: Preparing the Battery

Now take any old battery and take out everything from inside and take the battery case.

For doing this just use the pliers and open the case from top.

Then gently push everything upside and you will be able to get a battery case with six 1.5v cells and a battery cap.

Video Tutorial-

Step 13: Drilling Holes in the Battery Case

Now take the battery case and cover and drill holes in them as shown in the images.

And don't forget your safety is most important.

Video Tutorial-

Step 14: Assembling Everything Together

First take the battery cover and insert it into the USB port as shown in images.

Then secure the circuits by gluing them.

Now take the USB with the cover and gently push it inside the battery.

Then take the LED Matrix and push it inside the battery case and then gently insert the joule thief case.

Now take the battery case and insert it onto the other side of the battery as shown in the images.

Now take hot glue or super glue and seal everything inside. Do not apply much on the LED Matrix.

Step 15: Finishing Touches

Now, after completing the circuit work we decided to decorate it and do some creative work.

We just grabbed some white and red paints and brushes and started to paint it.

After some paint job we printed some labels for it and then glued them.

After getting some satisfaction and believing that it's up to the mark we left it to dry.

Step 16: Taking This Vision Further and Older Prototypes

Before making this prototype we have have made a few before and will make a few afterwards.

This section describes them.

Older prototypes-

  • It was a bigger version with around 25 LEDs
  • It had indicators to indicate charging and working,etc.
  • It had an on off switch
  • It had some space left to store something like 9v batteries.
  • It could charge 2 or more devices simultaneously.
  • It wasted energy as it didn't used joule thief and used 7805 for regulated 5v output.

Future Prototypes-

  • It needed ferrite toroid.
  • It needed only 4 LEDs
  • Less wastage of energy as no 7805 and use of joule thief.
  • Little in size; can be stored anywhere like in pocket.
  • It can charge only a device at a time.
  • It needs OTG Cable or something like that.

Step 17: Using It and Testing

For using it just grab your OTG Cable or something like that and plug your phone and LedUSB into it.

Then place it into the sun for charging. But what if there's no sunlight or you want to use this in the evening. Remember about, an extra battery cap and 4 rechargeable cells??

Just connect them in series and connect a battery cap to it and then just plug it into the battery cap of the LedUSB.

Step 18: Vote, Like and Share

This instructable means a lot to us.

If you like it please vote, like and share.

If you have any queries just comment them we will reply you soon.

If you like it you may also like our other projects.

Check out them here

More awesome projects coming soon.
Stay tuned.

Thanks for giving your precious time. Have a nice day.☺☺☺☺☺

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