# 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

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## 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.
Hoolaput4 years ago
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?
janw (author)  Hoolaput4 years ago
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:
 Value Preset voltage trigger point RoHS Compliant 1381C 2.0 (to 2.2) Yes 1381E 2.2 (to 2.4) Yes 1381G 2.4 (to 2.6) Yes 1381J 2.7 (to 2.9) Yes 1381L 3.0 (to 3.3) Yes 1381N 3.4 (to 3.7) Yes 1381Q 3.8 (to 4.1) Yes 1381S 4.0 (to 4.3) Yes 1381U 4.6 (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