Picture of Cheap Easy Solar Powered Robot
Make a very cheap, relatively easy to construct robot which will wake up any time you shine a desk lamp on it. There are no sensors on it, although I suppose the solar panel can be called a sensor. I plan on adding solar panels and another motor, and making it controlled by a PIC microcontroller in the future.

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Step 1: The Circuit

Picture of The Circuit
The circuit for the robot is very simple, it has no digital electronics. It's called a 'miller solar engine' ( and it allows a small solar panel to power a motor.

The solar panel stores energy over time by charging the capacitor in the circuit.

When enough energy is stored (this is sensed by the '1381' part) the energy is allowed to flow through the motor and the robot moves.

Then the whole process repeats.

In the circuit diagram, C1 is a capacitor, D1 is a diode, R1 is a resistor, and the circled M is the motor.


If you buy from, here are the part numbers for 1381 chips (they 'turn on'/'become active' at different voltage levels):

2v: MN1381-C-ND
2.6v: MN1381-J-ND
3v: MN1381-L-ND
3.4v: MN1381-N-ND
4.2v: MN1381-S-ND
4.6v: MN1381-U-ND

here is the part number for a 2N3904 and 2N3906


I got my solar cell from here:

If you can't find the stuff at those sources try these:
or do a google search for BEAM hobby stores.

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sjoshi33 years ago
Hey, U mean by flashing lamp light it works? Okay i am a tyro in this so please bear with me...If u find a way so that u can continuously flash light then the robot will work without stopping ryt? And anyway i can find a way to power a micro-controller with the solar panel??? Thanks a lot!
leevonk (author)  sjoshi31 year ago
flashing light would work too, but a steady light would work better. Yes, if you put it under the light it will keep running until the light goes out. To have the solar power run a microcontroller you would have to have the solar panel charge a battery which is used to provide the microcontroller with a steady electrical current (microcontrollers don't work on little bursts of current).
geeklord6 years ago
Wait a minute, if the 1381 chip goes off at at a certain voltage, wouldn't the thing go off constantly because its connected to the solar panel, or does C1 give it a time delay so that when it gets fully charged the chip aahhh, opens(?) the transistor????
it would'nt go off constantly because the solar cell's current is too low. Anyway the schematic is wrong, there needs to be a diode in series with the cap and cell
wobbler knektek4 years ago
The extra diode isn't needed in this circuit. The function of the diode when used in a typical battery charging circuit is to stop the battery discharging through the solar cell when there is not enough light to power the solar cell. Because this solar powered circuit only works when the sun is on the cell, the diode is superfluous. It would also, in this case, lose some of the voltage generated by the solar cell in the diode drop voltage and therefore make it more inefficient.
knektek wobbler4 years ago
But, the charging current will disharge through the solar cell and cause inneficency. But the diode is not manditory
wobbler knektek4 years ago
This circuit is designed to work only when the solar cell is actually in light, so the cell is always "powered up" and therefore effectively at a greater voltage than the capacitor, so there is no charging current to discharge through the solar cell as such. This circuit does not demand that the capacitor retains its charge when the solar cell isn't in light and so the diode isn't needed and there is no inefficiency without it in this case. However, if you were using a battery or supercap which you wanted to retain its charge when the solar cell was in the dark, it would be necessary.
knektek wobbler4 years ago
Exactly {O{_{O{
 theres so many different types of diodes which one did you use?

...Just use a high speed skotchy (spelling plz) diode. I would reccomend getting 3 in parralel so that there is almost no current loss.
wobbler knektek4 years ago
the MN1381 takes only microamps, so there is no need to use more than one Schottky diode, the others will just be wasted. The advantage of using a Schottky diode is that it has a lower forwards voltage drop over other diodes (0.15–0.45 volts versus 0.6–1.7 volts for a normal silicon diode) and hence less voltage is lost in the circuit where it is present. However, this diode only serves to raise the voltage at which the MN1381 triggers relative to your circuit ground, so using a normal silicon diode just means getting a different MN1381, rated approx.0.5- 1v less than the one you might have used with the Schottky.

paintsniper5 years ago
can u pls show me a top view or email me better pics to make it easier to build without using the schematic
 agreed im not gettin much out of this picture
leevonk (author)  thestyrofoampeanut4 years ago
I laid out my circuit exactly as the circuit diagram is drawn to show you that it is exactly the same and easy to go from the schematic to the circuit. That thing that says '100' is the resistor, that big cylindrical thing is the big capacitor, to the right of the capacitor the solar panel is connected. the bottom-most component is the diode. In other words, as I said,it's all laid out exactly as in he schematic,no tricks.

If you're a beginner it would be best to use a breadboard to make your circuit. Breadboards allow easy construction and modification of circuits without any soldering. Look up how to use them on google.
sparkspooky4 years ago
thats one big solar panel....=D
salahaddam5 years ago

They have some Solar Robots and Kits for sale!

geeklord6 years ago
I was gonna try using a 555 timer for this.
matejasj6 years ago
So we are trying to build the robot and are wondering what motor was used, we are struggling to find one that has a low enough current. Thanks!!
leevonk (author)  matejasj6 years ago
Unit042 leevonk6 years ago
no actually you linked to a different website. Solarbotics' website is We're dealing with an ecommerce storefront hawking robotics equipment, not OSS here...
I'm not sure what OSS is, but I only meant to provide an additional robot help website. I did not mean to correct your posted URL.
OSS = Open Source Software

in case you didn't know.

From first glance that website looked like an OSS website, but now I'm starting to harbor doubts...
Wasn't it also the current CIA, formed in world war two? Operation of Secret Services or somthin...
Thanks for clearing it up. Wkipedia says that OSS is some country somewhere, while google said... well... a that I got a couple hundred thousand hits on all different types of stuff that bear no resemblance to the context of your post. As to the site, well, if you click around, it's actually where some robot guys who run archived a bunch of solar-powered robot schematics. (Feel free to look at the website for longer than 10 seconds) In fact, it's probably where the schematic for the solar powered robot 'ible came from.
geeklord6 years ago
Ok ,this is starting to get annoying.......... In plain English what does a transistor do, beyond "amplifying and switching"?
Before I knew what those magical things did, I was just as annoyed as you are now....

Here's how to work one:
By running electricity from the base to the emitter, you allow an electrical current to flow from the collector to the emitter. This is useful because you can amplify a signal, or use the device somewhat like a relay to build logic gates and other interesting things.

NPN and PNP symbols with base, collector, and emitter labeled:

Ignore the pinouts of the transistors at the bottom of the page. Notice tthat the arrow's direction indicates whether the transistor is NPN or PNP type.

Hope this helps! :-)

The differences between NPN type transistors and PNP type ones lies in thier composition and therefore their behavior. an NPN type transistor will act like the transistor described above, and a PNP type transistor will act in the opposite manner. The gate is normally on, and it is turned off when a base - embitter current is applied.
yep, got that now
I'm not very old and I can't understand Techno-Talk, so I don't even know what to buy. From, Me
I want to make a 3V coin cell-powered robot like this. Would it be possible to use the coin cell, a capacitor, an NPN transistor and a motor to accomplish this (Cell charges capacitor, and when capacitor reaches voltage high enough through the base to trigger transistor, current from capacitor is let through to motor)? Thanks
leevonk (author)  Radioactive_Legos6 years ago
I think that should work, as long as the motor requires less voltage than the base trigger voltage of the transistor.
does anybody has the circuit diagram of this robot
i really wanna make this
n don hav money to buy d book or the PCB
nathan186 years ago
i just signed up and i need some help to get started
crazycade777 years ago
He yhow did you get the battery out of the CD player?
leevonk (author)  crazycade777 years ago
I got the motor out of a portable walkman cd player. there is not battery on this robot, it gets all its energy from the solar panel. To get the motor out of the cd player just tear it apart with a screw driver, or crush it with a hammer. the motor is pretty sturdy so smashing the cd player probably won't hurt it. Once you've gotten the cd player open just look for something that looks like the motor pictured. In cd players the motor shaft is usually attached to a screw looking thing (this is called a 'worm gear', it increases the torque of the motor).
HELP my Walkman is undisectable HELP
leevonk (author)  chemy9996 years ago
either patiently unscrew the tiny hidden screws or smash it with a hammer or a brick or baseball bat, etc. Wear safety goggles or glasses if you smash it.
i have unscrewed all the screws that I have found it still is keeping together p.s. i don't want to smash it
leevonk (author)  chemy9996 years ago
usually some screws are hidden under stickers or soft pad things or other things.
For example:
Do you need the worm gear and is there a chance people could buy a motor from somewhere?
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