Desktopfun! Build a Cute Little Flagwaver.

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 www.solarbotics.net 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 www.solarbotics.com . 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.