Since I've always did electronics through my Arduino and I feel I'm pretty much a beginner, I've never used a voltage regulator before. I want to create this circuit, but I want to hide it in my printer so I want it to work without a battery.
http://hacknmod.com/hack/beginner-spy-tutorial-your-first-diy-mini-fm-bug-transmitter/
I am planning to put a 3 V voltage regulator on it, but I wonder how hot a voltage regulator can get if the maximum voltage is used. And should I be worried about the heat, as in should a try to cool it?
Answer
The heat produced by a voltage regulator isn't a function of the voltage, it's a function of the power.
You can calculate the power the voltage reg will dissipate by taking the voltage-drop across the regulator, times the current flowing through the regulator.
E.G: $$Power = Volts * Amps$$
In other words, if you have a 30V source, and your device is running off 3V, you have \$30V - 3V = 27V\$ across the regulator. However, if your device is only drawing ~3 mA: $$27V * 0.003A = 0.081W$$
You would only have a dissipation of 81 milli-watts, which wouldn't even get too warm to the touch.
However, if you have a 5V input, with a 3V output (giving 2V across the regulator), yet your deice is drawing 1A, you have: $$2V * 1A = 2W$$
You have a power dissipation of 2 watts!
Basically, there is more involved in evaluating heat production then just the voltages
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