Introduction: The FLED Solar Engine

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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


rohanpsp (author)2010-05-30

 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

GreeceFallout (author)rohanpsp2014-05-04

It's the solar panel , you need more power from it

TXTCLA55 (author)rohanpsp2010-05-31

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.

rohanpsp (author)TXTCLA552010-06-03

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

TXTCLA55 (author)rohanpsp2010-06-10

Those are Bi-color LED's they will not work for this project.

sci4me (author)2010-06-17

actually, its always on. sorry.. help!!!!!!!!!!

GreeceFallout (author)sci4me2014-05-03

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

warboys (author)2014-04-09

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 :)

hplumbing (author)2013-11-27


themaddhacker (author)2013-04-20

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

TXTCLA55 (author)themaddhacker2013-04-21

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

harman65 (author)2012-12-26

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??

The Dragonborn (author)2012-06-09

Awesome Project ill do this soon!

dualqual (author)2011-07-29

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.

TXTCLA55 (author)dualqual2011-07-29

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

simplebotics (author)2011-02-04

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 :) !

TXTCLA55 (author)simplebotics2011-02-04

Thanks, I will!

sci4me (author)2010-06-17

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

rohanpsp (author)2010-06-03

 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

TXTCLA55 (author)rohanpsp2010-06-10

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.

meerut260 (author)2010-04-09

Where to buy cheap solor cells for these projects. It will be a great help if block diagram is also added with project

TXTCLA55 (author)meerut2602010-04-11 is a great website for cheap solar cells, or you can go to your nearest radio shack or the source by circuit city but they tend to have limited or no supply of powerful solar cells like those you would use in this project. as for the diagram i will start work on one as soon as possible as i do realize the hand drawn one isn't as helpful as i hoped. 



thestyrofoampeanut (author)2010-03-10

 ive been having trouble with this little bot for a while due to a number of silly reasons
i finally got a fled that works with my voltage
i hooked it up DIRECTLY to the solar panel and it works fine
does this mean i dont need the resistor?
my radio shack solar panel says 6V but i really think its putting out less, its kinda crappy

No, the resistor is there to "level" or "steady" the off and on current; protecting it from the pulses of the solar panel. If you need a better solar panel I suggest buying one off of this website they may not be cheap but they are high grade. Oh and a word of advice...because of their prices I would buy a bundle of things you may save some money if you need parts later on. Hope this helps!

beannie (author)2009-10-04

can I use a 6v solar panel?? what change would be needed in the circuit??

salahaddam (author)beannie2010-02-19

 Best to add some diodes to the circuit for higher voltage solar panel.
 Then you get higher trigger level.

 Checkout my Solar Robots and  Kits

salahaddam (author)salahaddam2010-02-19


TXTCLA55 (author)beannie2009-10-06

Hmmm you could. But the power comming off it may be a little too much for the FLED. if you really want to you can add a resistor.

 i also want to use a 6v solar panel
if i put in 2 FLEDs in series instead of one would that work?

yes it would still work.

salahaddam (author)2010-01-09

 These are just like the robots at

abdul moiz (author)2009-12-20

Can u plz give the specifications of the solar panels to be used ( i mean voltage and current specifications).
It would be kind of u if u  gimme a link of the site to purchase it too...
          thanx in advance..

TXTCLA55 (author)abdul moiz2009-12-20

The solar panels I used are rated for three volts, the amps I am not sure though. As for where to buy these parts, you can check out this web page  and search thier components for all the parts exept the resistor, which you can probably scavenge out of a toy or other electronic equipment (that's how I get most of my parts). They also sell kits that feature many of the principals in this instructable (Ex: The Solar Roller Parts Bundle or the SolarSpeeder V2.0 They (the kits) can be a bit expensive at times, so I would suggest you just buy the parts. Hope this helps! And all the best in your future projects!

milsorgen (author)TXTCLA552010-01-06

they have solar panels at most radioshack locations, easier to get those than breadboards where im at lol but i dont think they are putting out as much power as the board your using

worth a shot for those of us who dont like to wait tho ;)

abdul moiz (author)TXTCLA552009-12-20

 Thanx bro..i hope it helps.. :) ...

abdul moiz (author)abdul moiz2009-12-20

 The maximum size of the boat which is to be prepared is 25*20*20 cm^3 ..
i was concerned with the area and the number of the solar panels to be used..
it would be great if u refer to this link and solve my problem

milsorgen (author)2010-01-06

optical drives are a good place for motors, found upwards of 3 in some older CD-ROM drives

peterjacob (author)2009-12-25

thanks for this :3

beannie (author)2009-10-08

I have a solar cell that can output 4.5v. But the problem is it only provides very little power and it still takes a long time to charge the cap.. what would I do??

TXTCLA55 (author)beannie2009-10-10

Well i would suggest you try using a bunch of small caps together (so they make up one large cap) or try and find a better solar panel. Hope this helps! let me know if you still have problems.

imakethings (author)2009-08-25

can i use a 1.5 v solar cell?

TXTCLA55 (author)imakethings2009-08-25

Yes you can use a 1.5v but you will need to use two because the FLED, the prime component must get 3.0v to function. So if you were to use two the circuit woul work; and thus one would not. Hope this helps you and good luck building the project!

Colonel88 (author)TXTCLA552009-09-28

no u can use a single 1.5 volt but it would take a hell lot of time to charge the cap

imakethings (author)2009-08-27

IS it ok if i do not add the FLED? and put a jumper wire in there?

Colonel88 (author)imakethings2009-09-28

no because the FLED is the "timer" in this project without it it would not work

TXTCLA55 (author)imakethings2009-08-28

No the FLED is the pluse emitter with out it's steady impluses the circuit would not work. If you test the circuit your self you will see that the motor will not turn. I hope this answers your question.

confudled person (author)2009-08-07

nice pic !!!!!!!!!! :)

chickenz56 (author)2009-06-07

whta if we use a normal led. not a flashing one

TXTCLA55 (author)chickenz562009-06-07

The FLED provides a pulse current which controls the engines output. If there is no pluse circuit, and a regular LED is used, this pluse that would normaly drive the motor would not exist. thus the motor would not turn. the Fled also allows the capacitors to recharge (every "off" pluse) thus they can charge up again and emit that charge to the motor whe the FLED thurns on again.

rockendrumer (author)2009-05-30

on the how to make a dooms day survival box it talked about a solar charger and created a link to this Instructable, and I was wondering how to make a solar charger out of this (I don't wana make a few to understand how they work to make one) so if some could help me that would be great

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