Desktopfun! Build a Cute Little Flagwaver.




Introduction: Desktopfun! Build a Cute Little Flagwaver.

About: I'm mainly interested in music, food and electronics but I like to read and learn about a lot more than that.

It's cute, it brings a bit of fun onto your desktop, it makes everyone smile when they see it moving and even your girlfriend will tolerate it in the house. Yes, it's a tiny flagwaver.

It is a perfect project if you are new to electronics. You can have a very nice result in no time and almost nothing can go wrong.

English is only my 3th language so please forgive me if I made a mistake somewhere.

I used 2 schematics in this instructable. They both are from so they get the credits for those

Step 1: How Does It Work?

The circuit we need to make the flagwaver wave its flag is a basic solar engine. More specific a 1381 - based solar engine.

Most small solar cells aren't able to  make a motor spin when connected directly to it. So we need to store all the energy of the solar cell until there is enough for the motor to run. Thats where we need the capacitor for. Slowly it fills up until it reaches the desired voltage. The 1381 - voltage supervisor IC trips when the voltage meets the desired level and it puts the voltage to the base of the 2N3904 transistor. That opens the gates for the current to go through the motor and so the motor spins. At the same time the 2N3906 is opened. This allows the current to pass around the 1381 so that the capacitor can be fully drained. Otherwise the 1381 would shut down the circuit it the voltage drops below its trip - point.

Result: The flagwaver will come alive with little bursts of energy an it will wave its flag happely ever after.

Step 2: What Do You Need?

Here is you shoppinglist:
  1. 1 x solar cell. I used a 22mm x 24mm solar cell from . It has an open circuit voltage of 3,4V and a short-circuit current of 12mA.
  2. 1 x 4700uF capacitor.
  3. 1 x 2N3904 transistor.
  4. 1 x 2N3906 transistor.
  5. 1 x 1381E Voltage supervisor. The 'E' stands for the voltage at which the IC trips. In this case it is 2,2V.
  6. 1 x motor. I salvaged mine from a DVD-player.
  7. 1 x 2.2kOhm resistor.
  8. Some wires to connect everything up. Also salvaged from some electronics junk.
  9. Glue. Can be hot-melt or construction-kit or whatever you fancy as long as it is sticky enough to hold all the parts together
  10. A Flag. What else would it wave with
I also used some heatshrinking tube to attach my flag and to give the cute little fellow a bit of color.

Appart from this list, you'll need a soldering iron, solder and something to cut the wires.

Step 3: Connecting the Capacitor to the Solar Cell.

  1. Bend the leads in a way so that they fit onto the + and - pads on the solar cell. Make sure that the negative lead is connected to the negative pad and the positive to the positive pad.
  2. Glue the capacitor to the solar cell.
  3. Solder the leads onto the pads.
Simple to start with, isn't it?

Step 4: Building Up the Brains.

  1. Glue the 2 transistors and the 1381 together as shown in the images.
  2. Connect the leads as shown in the second picture. Do this by bending one of the lead towards the other and solder them together. After the soldering you can cut the leads close to theire connectonpoint.
  3. The rectangle in the second picture is the resistor. Glue it to the side of the 2N3904 and solder the leads.
  4. You should end up with something like in picture 3. Don't worry about the motor and the positive and negative connection yet. That will come in another step.
Well this was really the hardest step of them all.

Step 5: Attaching the Brains.

  1. Glue the 'brain' to the capacitor as close as possible to the negative lead of the capacitor.
  2. Bend the lead down and solder it to the brain on the appropriate spot (see picture). if you can't reach the brain with the lead you will need a small piece of wire to do the connection.
  3. Connect  a wire to the positive connectionpoint. We'll need that later.
We are nearly done.

Step 6: Making It Wave!

Well if we want this thingy to wave a flag, we'll need to connect one more thing: the motor (and a flag).

  1. Glue the motor to the capacitor. The metal casing of the motor isn't always very easy to glue so I used some heatshrinking tube around it to make it stick better.
  2. Solder the loose wire (coming from the positive connectionpoint of the brain) onto one of the terminals of the motor.
  3. Connect a wire from that same terminal to the positive lead of the capacitor. You can cut the unused part of the lead after that.
  4. Now we just need one more connection. use another piece of wire to connect the second terminal of the motor with the correct lead on the 2N3904 (see picture).
  5. Now you can attach a flag to the shaft of the motor. Choose any flag you like. I won't help you there. I attached mine with some heatshrinking tube. I used multiple layers of it until the flag was connected firmly.
Wow you finished it!!!

Step 7: Testing It.

Place you flagwaver under a bright light (as bright as you can find). It should start waving at you within 1 or 2 min. If it doesn't do that, something went wrong.

First thing to check then are all your connections. Maybe some wire is not attached.

Check also the leads of the brain. They should not touch each other on other spots than the connectionpoints.

Those are the two big things to go wrong. Normally by checking them you should find the cause of your troubles.

Be the First to Share


    • Pocket-Sized Speed Challenge

      Pocket-Sized Speed Challenge
    • Metalworking Contest

      Metalworking Contest
    • Maps Challenge

      Maps Challenge

    9 Discussions


    10 years ago on Introduction

    nice instructable!!
    alright 2 questions if I use another voltage supervisor like 1381U will the trigger voltage be different so instead of 2.2v it's gonna be 4.6v? and also if i take out the 2N3906 transistor and the 2.2k ohms resistor the motor will stop running if the voltage across the capacitor is less than the trigger right?

    one more question =) if the voltage across the capacitor is above the trigger (let say I added a button in series with the motor for some reason) will the voltage supervisor still send a signal to the 2N3904?


    Reply 10 years ago on Introduction

    Every 1381 has its own triggervoltage so you have to look up in the datacheet what de voltage for your 1381 is. Here is a list of the most commen:
    ValuePreset voltage trigger pointRoHS Compliant
    1381C2.0 (to 2.2)Yes
    1381E2.2 (to 2.4)Yes
    1381G2.4 (to 2.6)Yes
    1381J2.7 (to 2.9)Yes
    1381L3.0 (to 3.3)Yes
    1381N3.4 (to 3.7)Yes
    1381Q3.8 (to 4.1)Yes
    1381S4.0 (to 4.3)Yes
    1381U4.6 (to 4.9)Yes

    Indeed if you leave the 3906 and resistor out it will stop when the voltage drops below the triggervoltage of the 1381. those 2 are added to drain the capasitor completely.

    If you added a button, the 1381 wil sent a signal to the 3904 but the motor will not spin because you disrupted the current there. As soon as you press the button the motor should start.

     this is a cool project and great for beginners 
    and if english is really your 3rd language thats amazing how good you are at it because it's a complex language


    10 years ago on Introduction

    Cool! I'm thinking this could be the basis for a cat toy to keep them entertained thourhgout the day...


    10 years ago on Introduction

    I've got a couple of solar cells on the way for something similar.  Not quite sure what yet, but I've got a few ideas.
    The short, fat motors which operate a CD / DVD drive tray are pretty good for this type of thing.  They will work down to a couple of volts.


    Reply 10 years ago on Introduction

    Yes indeed, motors out of CD / DVD players are great to work with. For this one I used a tiny motor out og a DVD-rom station. It was used to open and close the player.
    If you want really tiny motor you should salvage them out of digital cameras. The motors used to open and close the lens are really small and run on next to nothing.


    Reply 10 years ago on Introduction

    I salvaged these 2 from cameras. I added a 5mm led so that you can estimate theire size.


    10 years ago on Introduction

    I agree, a great way to get into simple robotics, and to practise your soldering skills.