This is my first post here. I looked at Arduino online for a few weeks learning as much as I could and finally ordered one last week. Its been a while since I've done anything with electronics and my knowledge is pretty basic.
My first task is finding a suitable power supply for the Arduino (Mega) that is ideally AA NiMH batteries since I have many extra rechargeable AA batteries around from my camera flash unit. I've got a 8 cell AA battery holder and a Radio Shack 7805 voltage regulator (5V output, 1A max current, 35V input max). Its hooked up right now and going to the VIN and GROUND on the Arduino and working and double checking the voltage shows 5.01V.
Is this something that I can use to power the Arduino safely and everyday? Is there a reason why I shouldn't use a voltage regular and 8 AA cells? Sorry if its a dumb question but would rather ask a dumb question than fork over another $50 for a new board if I fry something. Thanks for your help!
The Arduino Mega already has its own voltage regulator, you could attach your battery pack directly to the VIN pin, or the barrel jack.
You're also using a 12V source to get 5V, meaning that you're throwing away more than half of the power you use, as heat. You may want to find a battery holder that gets you 7.5V or 9V, closer to the desired voltage but with enough headroom for the regulator dropout.
Glad you're trying things before asking, though. A lot of people get hung up asking questions before they do every little thing, and as a result their progress is extremely slow.
There is also more efficient way - use more than 2 batteries and switching regulator with 5V output (MC33063 ...) . Linear regulators (like 7805) change P = (Vin-Vout) * I into heat.
The ATMEL 168/328 will run on quite a range of voltages. Using NiMH batterries there shouldn't be an issue wiring 4 of them straight to the 5v input. Providing the voltage doesn't go above 5.5v it should be OK. If you're using Alkalines use 3 cells instead of 4. they are quite happy running at 3 volts, whether the same can be said of the circuits that are powered from the arduino is a different matter.
The ATMEL 168/328 will run on quite a range of voltages.
It will run at a range of voltages, but it will notprogram at all those voltages. Do not try to upload a new sketch with anything less than 7.5V at the DC input jack/9V pin, or 5V at the 5V pin. Also, be aware that anything less than these voltages will result in garbage analog input operation, since there is no stable/known voltage to use as a reference.
Just a minor clarification, the Mega has a low dropout regulator so you can drive it with 6 volts on the Vin pin or around 6.7 volts on the DC input jack
You can run the ATmega168P/328P down to 2.7V if you lower the clock frequency
to 10MHz. Check the Maximum Frequency vs Supply Voltage graphs in the datasheet.
Be careful when choosing a linear regulator for use in your battery system.
When your input voltage (Vin) is less than the sum of your output voltage (Vout)
and the dropout voltage (Vdo) then your linear regulator is not running in a linear
mode -- it is a saturated switch and will not regulate.
For 2AAs I would use a boost converter (either to 3.3V or 5V).
For 3AAs I would probably use an LDO (with a Vdo of few hundred mV's) to
get 3.3V and use a 12MHz XTAL.