I'm starting a project that involves playing an mp3 to an outdoor speaker, or speakers, based on a triggered event detected by an Arduino. I've already got an Arduino Uno and the mp3 shield from Sparkfun working properly and playing a file from the mini SD card. The next step, in my mind, would be to output the signal from the mp3 shield to some sort of amplifier to drive the outdoor speakers. This is where I'd like a little guidance. The ideal case would be where I don't need to have a consumer grade receiver/amplifier powered on all the time in case the event is triggered. Is there such a thing as an "instant on" amplifier that can be powered on rapidly by an Arduino "on demand"? I've seen amplifiers like the Kemo M034N 40W amp:
For the board amplifiers, they strike me as needing to be continuously powered, not "instant on"... I suppose I could have an amp that is usually powered off, and then energize it with an appropriately sized transistor of some kind, but that strikes me as a major hack and not likely to work fast enough because of latency issues... Is the Kemo amp actually enough to drive a typical outdoor speaker?
Well either of those amps will drive those 'rock' speakers fine, they are just rather standard 8 ohms speakers, just hidden inside an artificial rocks.
Both of those amplifiers require a separate DC power supply to power the amp boards. It's this power supply that you would want to turn on of off via your arduino at the correct time. You could use a simple relay to control the AC input power on and off to the power supply AC input.
Don't forget you have to determine how you are going to set-up the playing volume for the speakers as I'm not familiar with how a MP3 shield controls volume, but if it doesn't you will need a volume control pot between the MP3 audio output and input audio of either of those amps.
Ah, that's a relief indeed because I think it would simplify the circuit if I could use the Kemo amp I linked to above. I definitely understand the need for a power supply that can feed the current that the amp needs because the Arduino can't supply that kind of power... Wouldn't it be possible for this power supply, if sized correctly, to power both the amp and the Arduino at the same time? In other words, the power supply would feed a circuit that would send 9 to 12V and ~500A to the Arduino and 6-16V and 4A to the amplifier? Is it unorthodox to wire the arduino this way?
Generally not a good idea to put disparate loads on the same line. However, you can isolate the mcu from the power amp, for example, through a diode + capacitor.