The FLED Solar Engine





Introduction: The FLED Solar Engine

Ever wanted to make a BEAM robot, but couldn't find a easy circuit to build? Well, meet the FLED solar engine! The robot works by collecting sunlight in the capacitors, then when the voltage is just right the transistors turn on allowing a pulse of electricity, this pulse travels to the FLED (Flashing Light Emitting Diode) which gives the motor a quick turn, then the cycle repeats. The most important part of this project is the FLED which essentially control's most of the electricity generated, so if you use a regular LED the circuit will not work. Now let's get started.

Step 1: Materials

You will need the following materials...

A solar cell with an output of 3vDC (Volts Direct Current)
At least a 1400 uF Capacitor (or more)
A 2.2K ohm resistor 5% (color bands are Red, Red, Red, Gold)
2N 3904 Transistor
2N 3906 Transistor
Motor (make sure it runs on 3Vdc, most do, but just to be sure check with two AA batteries)
FLED (flashing LED)

I got all my components from ripping them out of toys and buying them online. You can try or or ebay.

you will also need:
a soldering Iron (any cheap one will do)
some solder ( a small/ thin size works great)
a pair of Extra Hands (can buy online or at Radio Shack)
and a sunny location for testing

Step 2: Understanding the Solar Engine

The solar panel creates engery from sunlight, the engery is stored in the Capacitor(s), when there is enough power the transistors allow the current to be released to the FLED, because there is a flashing circuit in the LED the current is controlled and let out in short bursts of engery, the burst of engery travels to the motor, the motor shaft moves and the robot shifts forward. Some of you might be asking what the resistor is for? Its basically there to control the amount of current coming out of the transistors to the FLED (so the FLED wont burn out and die).

Step 3: Putting It All Together

I found out that it is a lot easier if you follow the pictures, like you would on a jig saw puzzle. In the same way you to can "connect the components" by looking at the picture.


Polarity Rules for FLED, LED's, and Capacitors

- Capacitors have a line on their side that is a different color that the other more dominant color, this is the negative. Ex: a Capacitor is blue all over except a black line, that would be the negative.

-FLED's and LED's have a flat side around the bottom of their base, this is the positive lead. Ex: a green FLED has a circular base and a flat side near one of its leads, this is the positive lead.

Once you have followed the diagram below and have soldered everything up it is now to test or troubleshoot the Solar Engine.

Step 4: Testing and Troubleshooting

Ok time to test it out. take a marker and mark a spot on the shaft of the motor, anywhere will do but just make a dot. Now put the solar engine in some sunlight and if the shaft moves you should see that dot move. if it works, you have created a Solar Engine. If it doenst move for about 6 minuites its time to troubleshoot.

Here are some common mistakes:

bare wires touching
bare wires touching metal that touches other bare wires
to big of a capacitor, and taking to long to charge
not enough power comming from solar panel
broken motor
any broken/ really dammaged component
wrong components



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    79 Discussions

     please please please help me .i have made the circuit correctly.checked 5 times.i connected 3 volts to it the fled starts on off on off but motor do not spin.after shorting fled the motor to correct my circuit

    4 replies

    Its unfortunate that this happened to you; I would suggest you restart your circuit. or at the very least check for any other shorts, bad connections, wrong components, anything that isn't described here...remove. Also you might want to replace the FLED. the problem could also be the motor, check to make sure it requires a voltage of 1.5 no less, I think the FLED needs 2-3V  either way the FLED and the motor put together should requre a total of 3v (hence the needed 3v solar panel) if the required voltage is greater than this the circuit wont work. I hope this helps you solve your problem and please contact me if your problem continues.

     i do not have fled but i used 2 in one color led means one color then it changes to another color.

    I have the very same issue , when struck by light it works continuously...
    About the others saying it's not working there is a small possibility that you damaged the FLED or transistors during the construction

    I have built the FLED solar engine and mine is sort of working. But I don't have a solar panel so, I replaced it with a 5v dc motor that I crank by hand. I have all the correct components and also have checked for bear wires touching.

    So my question is should the capacitors charge up before the switch is triggered to start turning the motor?

    In my case the capacitors are charging up but then dumps the charge immediately. I have to crank the dc motor pass 2.10v for the other motor to start turning.

    Any ideas would help

    Thanks :)

    I just built this circuit and it works good could you change the caps to drive a bigger motor?

    1 reply

    Possibly, but the it would take longer for the solar panel to charge them up. Unless of course you upgrade the panel as well.

    i am using a 6v,250mA solar panel and want to run a 12v,400mA motor using it, so can u tell me what resistor and capacitor values shuold i use??

    Great Instrucable! There is one error though. You stated above, that the FLAT side of the LED represents the Positive, or Anode lead. Actually, the flat side of the LED represents the negative, or Cathode lead.

    1 reply

    Oh true, well as long as you follow the diagram it should work. Thanks for pointing that out!

    hey cool symet, i just completed my first instuctable on how to build one too! if you want to see it check it out or just visit my blog at, and thanks :) !

    1 reply

    i have the same problem but i have a fled. i have checked ten times!!! help!!!!!

     you have to improve this fled solar engine.please try to make a your photos of fled there are two leds more capacitors.but your is different.make fled solar engine according to circuit components and a photo of circuit.plz

    1 reply

    I am sorry for the instructable's crappy nature. Believe me I too want to redo it, its just finding the time, with finial exams coming up and everything else. When I have the time I will post proper pictures and circuit diagrams.