After calibrating in software...  I've been able to get 1sec/10 days drift with Arduino Uno.  Assuming the temp is constant.

Love your Simulator!  Looking forward to the new version!

If you can find an old 50w PS and your laptop needs 65w it will do exactly what we want it to in Windows 7: Not charge.  When you go traveling just bring the 65w.  Simple!

Wow!  Flashback.

Sounds like you don't need the SD card if you're going to send it every 1/2 hour?

That makes sense to me.  You can only go 7RPM when you change directions without a delay.  You can go 14RPM in one direction.  The solution is simple.  Go 14RPM, then stop for a short delay before changing directions.  It's easy to calculate the delay using 7RPM.  It's just twice the delay between steps at 14RPM.

Why not use 12V as in my code?  You can change the duty cycle while moving so it never gets warm.  Increase it back to 100% for 1 step before and after you change directions.  This will give you 30RPM without any delay, even when changing directions.  That's 4x faster.

You can use a transmitter and cheap receiver.  If it receives turn it off.  If not on.  It will be on more often when it is further away.  It will not be a circle and it will go on and off even in the same spot.  You will need to experiment.  The good news is that you can experiment while you are holding the unit.  By adjusting the power or transmit antenna you may find you get decent results.  Give it a shot!

RWiens, Just try it and enjoy!  Any suggestions for improvements? 

When I'm finished making improvements I'll make it into a real Library.

I can fix my code to work with 4075+.  All I'd need is a motor to test it.  Already the code is able to rotate by 0.36 x 1000 to make a full revolution.  Notice the step size is not even close to a multiple of 0.36 degrees.  The only disadvantage is the need for floats the way it is written.  Who wants it?

I have posted a schematic in another thread where you asked.  It's as simple as calling this function in my code.  All you have to do is calculate the speed in RPH using y and x.  Need help?

void degrpmslowCool(boolean bcw, long deg100, int rph100)

Check out the beginning of this post.  You can test my code with only 1 line or by uncommenting a few lines in my Setup()/Loop().
http://arduino.cc/forum/index.php/topic,89159.0

Here's the newest code:
https://gist.github.com/sbright33/4178431

Start with this in loop():
degrpmslowCool(1,180*100,1000);  //180 degrees at 10 rph speed

which calls:
void degrpmslowCool(boolean bcw, long deg100, int rph100)

For those of you asking for help check out the beginning of this post.

Here's a schematic for you Sharon.
http://arduino.cc/en/Reference/StepperUnipolarCircuit

I'm nearby if I can help.

Here is the newest version for 28BYJ-48.

https://gist.github.com/sbright33/4178431

12v is reliable, you just have to mind the heat.  This means you cannot run at full speed for 20 minutes.  You can go slow forever using the "cool" functions.  Or go full speed then stop to let it cool down.

What he said.  Seriously.  My code does support acceleration in many of the functions so you can achieve the results in AccelStepper library without any effort.  Even using 5v.  12v is capable of going much faster with the only difficulty that celem mentioned.