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hello there,

i have an arduino uno and would like to plug an audio speaker (5W -not 0.5W- 8 ohm).
would anyone have the kindness to tell me what resistor should i use for it? (and explain the calculation behind it so i won't bother again ;P)
as a note i've already checked the "arduino tutorial tone". but got scared trying since the wattage of the speaker wasn't revealed...(or does it make sense or matter?)

thanks a lot!

alex, lost in space
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hello there,

i have an arduino uno and would like to plug an audio speaker (5W -not 0.5W- 8 ohm).
would anyone have the kindness to tell me what resistor should i use for it? (and explain the calculation behind it so i won't bother again ;P)
as a note i've already checked the "arduino tutorial tone". but got scared trying since the wattage of the speaker wasn't revealed...(or does it make sense or matter?)

Ohm's law isn't difficult...you'll be glad you made the effort to do it on your own.
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There are really two independent issues here that you have to address separately.

1. An arduino output pin always needs external protection from trying to draw too much current from the output pin. A 8 ohm speaker (of any wattage rating) will draw too much current if directly wired to a arduino output pin. Adding a series resistor between the output pin and the speaker will protect the output pin, and 150 to 200 ohm resistor is a good choice. However this resistor will severely waste most of the 'audio power' and prevent the speaker from having very much volume at all.

2. A speakers 'wattage rating' is it's maximum power handling ability, sort of how high a volume it can attain before distortion sets in or it burns up. To drive most any speaker to whatever maximum value it can handle requires a audio amplifier rated at near the same value of the speaker. But keep in mind that people run their amplifiers and speakers using a volume control to the volume level they are comfortable at listening to. I have a vintage 70s hi-fi system where the amplifier is rated at 250 watts RMS maximum output per channel and I'm driving two large 12" 3 way vintage speakers rated at 50 watts handling power. I can fill my room will very loud music where the amplifier is supplying around 2 watts of average output.

So keep in mind what you are trying to attain and that any speaker sound you wish to generate from an arduino project will require at least a small audio amplifier, one or two watt amplifiers will work just fine  with nearly any speaker rated at 8 ohms.

Lefty
« Last Edit: November 23, 2012, 10:13:04 am by retrolefty » Logged

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This is what I use to get speaker output in my Arduino projects, its loud enough, easy to build and you should be able to find the parts easily enough. You can hear it in action in the link -

http://rcarduino.blogspot.com/2012/08/adding-audio-to-arduino-projects.html

Duane B
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And here is a cute and inexpensive stereo amplifier I ordered yesterday on ebay. This one can even have the arduino control the volume ouput via a couple of output pins!

http://www.ebay.com/itm/350604041652?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Lefty
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Thats a good deal

Duane B
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I once used a pair of free headphones they gave me on a train journey as Arduino speakers (perks of travelling first class).

I wired both of them to an Arduino PWM pin (with a resistor of course!). The beep for "job done" was loud enough to hear in the next room.

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