razboss:
No, sorry but I forgot to specify what I am using this for.
I want to make a pseudo-NFC transmitting device (google poor man's NFC). It essentially uses a magnetic field to transmit data one-way to a device with magnetometer (an Android phone). The coil will be used to create the magnetic field and also will be switched on and off pretty fast (once every 90-100 ms: ~10bps). This experiment is for educational purposes only and I don't want to accidentally fry the Arduino board because of a small experiment with no purpose in real life.
Thanks for the answers provided so far!
Not sure what NFC stands for (near field communications?) but the the design of the coil will not be based just on it's DC resistance, but also on it's induction value which will determine it's impedance at your choice of frequency of operation. So you are therefore working in the world of AC theory not just basic DC theory. As such you are really just describing an RF information link. An RF signal, once propagated from the circuit, contains both a E field wave (electrical) and a H field wave (magnetic) that encompassed what a electromagnetic wave is composed of.
So I suggest you study and research simple RF communications methods and circuits. You will need to know more specific information about the magnetometer sensor on the Android, such as what is it's frequency response range. A raw CW (Morse code) on/off type signal rate of 10bps would result in a 10Hz carrier frequency which would require a huge induction value for the coil usually requiring a iron core, much like 50/60Hz rated power transformers, which might be impracticable for you project, depending on specific power level desired for whatever your specific maximum 'near field' distance requirement is, which is then dependent on the sensitivity value of the magnetometer. Better to utilize a much higher 'carrier frequency' (but still detectable by the magnetometer) which you can key on and off at whatever slow information rate you wish. Again focus on the specifications and capabilities of the magnetometer first, it's frequency range, sensitivity, etc, that will dictate what is possible and practicable.
Lefty