So anywhere you look it says that to reset an Atmega you have to switch the reset pin from high to gnd for a quick moment. That's what the button is for. But what you wanted to have one arduino decide when to turn another one on... could you hook the reset pin of the second arduino to the first arduino, and keep the reset on ground, thus keeping it off, until the 1st arduino switches it to high, thus turning it on?
Or does this damage the chip?
I know you could achieve this with a transistor hooked up to the power of the second chip, but lets say I was adventurous today.
*Erm, when I say arduino, I mean standalone atmega chips, properly wired and bootloaded and all.
This should work and is a technique sometimes used. As long as the reset pin of the chip you driving doesnt source too much current. Check the AtMega Datasheet to see if that is within spec and it should work.
As long as you keep the chip in reset it wont execute its program. Just remember that if you have a in circuit programmer hooked up to the chip you could get problems
No you can keep the chip in reset as long as you like. You normally only use a 10K resistor to +ve so there is no great current draw.
Holding a processor in reset is quite a normal thing to do in a bigger system especially when you have a complex booting system that involves two or more stages.
In cases where you have a series of boards like this and you want a 'master' unit to control the reset of the 'slave' boards, it might be more stable/reliable to wire external pull down resistors on the slave units reset pins that the master could then pull high using a digital output pin. That way the default for the slave units would be held in the reset state, even if the master board is reset or powered down or being reprogramed or whatever.