USB Rechargeable Flashlight

Introduction: USB Rechargeable Flashlight

In this instructable I will show you how to make a flashlight that charges within seconds and lasts for about one hour. All with USB! Please tell me about how I am doing on this Instructable. This is my first. Thank you. A while back Trialex posted this instructable. His instructable gives calculations if you need them. 

Step 1: Buy Parts

The parts you will need are

1. A 1 farad 5.5 volt super capacitor

2. A male USB connector. (You can cut a USB adaptor and use only the red and black wires or + and - connections

3. A normally open push button switch

4. (Optional) A toggle switch

5. A perf board or etched circuit board

6. A Led any LED works as long as it is not above 4.5 volts. Preferably with built in resistor. You can also use this color changing LED

7. A resistor if your led does not have one.

8. Wires if you are using a perf board

9. A usb charger. (You may be able to use a computer USB port but I don't take any responsibility for any damages to your equipment.)

Most of the parts can be bought from They have the very best prices that I have seen so far.

Step 2:

Build on perf board or etched coper clad board. You must have some soldering skills to do this project. Check all of your connections before plugging into USB. You do not want to short your connections.

Step 3: Finished Product

If you made one of these post it in the comments. I would like to see how helpful this instructable was.



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    25 Discussions

    Nice instructable, but your embedded video no longer exists. Please fix.

    Just a note: A capacitor will draw a high current at the start of its charge, and this will reduce as it charges. The current when the capacitor is at 0V is theoretically infinite (so in practice, fairly high). This isn't really the sort of load you want to be putting onto a USB socket, even if it is current limited (are they at all?). A suggestion would be to put a 50 ohm, 0.5 watt resistor in series with the capacitor. This would limit the current to 100mA, which is the standard maximum current that can be drawn out of a USB socket without negotiation over the USB protocol.

    so im trying to figure out what kind of super-cap i need to power an led flashlight for an hour. i tought the idea was 1F = 1 Amp/second, so if you drew an amp, it would run out in a second, but if you drew 10 mA, you would have power for 100 seconds.

    if you're saying this will last for ~hour then my formula doesn't jive well. Am i missing something else here?

    1 hour = 60 minutes = 3600 seconds,

    1000ma / 3600 = ~.30 mA per second. i don't know any LED's that will light up at all with that little current...


    3 replies

    Also, this is a 1 fared capacitor at 5.5 volts. This LED only draws about half of that at about 3-5 mA. The LED also dims quite a bit after about a half hour.

    "Low current LEDs" can operate at currents below 5mA, although most of these are red.

    How long it lasts depends on the led and resistor you use. It also depends on the charge time. For me after about a half an hour the led gets quite dim. If you use a larger resistor the led will stay on longer. You can also try building a joule thief or a D.C voltage booster to light up a low current led for a longer time. A neon lamp requires very little current so if you boost the voltage high enough you may be able to light it up for quite some time. Thanks for the reply.

    Can everybody please rate my instructable so I know how I am doing. Thanks.

    If I were to add more caps I parrerell would it last longer, or a cap with more ufs then just one uf?

    3 replies

    Yes, but I believe that if you wire the capacitos to gain a higher capacitance, the the voltage will be cut in half.

    Actually, if you wire them in parallel, you'll add up capacitance without any voltage loss ;)

    The problem will appear if you wire them in series: you'll surely have more voltage, but here the capacitance will be hugely reduced...

    Great idea.
    Have you thought of replacing the capacitor with a CMOS baterry? Little changes in the setup and will last a lot longer and can add another LED. What about a picture of the backside. With a 1 foot long cable can be used to light the keyboard while connected to the laptop.(for those times you are in bed and do not want to disturb your roommate). Once encased, just push the cable inside of it with theplug, Both will be protected at the same time, more transportable,

    1 reply

    Great ideas. Unfortunately I do not have a CMOS battery and do not know where to get one. If you decide to try it I would love to see the pictures. Thanks!

    hi....why does the push button switch did not include in the schematic diagram??? tnx....

    1 reply

    I think you mean the toggle switch. I built the diagram before I made it. So I came up with the idea to have the toggle switch while building it.

    I loved it.It was excellent and so easy also.