# Questions on Uno w/Speaker

Hi all,
I’m currently working on achieving a decent wattage/volume output from my speaker with my Uno.
Here’s what I’m using:

-Arduino Uno
-4 Ohm/10W speaker
-Arduino Tones tutorial

Please correct me if I’m wrong here.
I believe the Uno’s max mA output on the digital pins is 30mA, and because the Uno has a 5V output I need a resistor of about
160 Ohms…that’s still only .15 Watts, and unacceptably inaudible for me.

My questions are: does higher wattage equal higher volume as I suspect, and how might I increase wattage/volume in my circut?

You need an audio amplifier...

You need an audio amplifier...

Increasing mA's or V's would increase wattage. That's what an audio amplifier would do, and that's what I'm asking how to build.

Emitter follower will increase mA proportionally to h21.

That's a bad circuit for driving a speaker. A speaker requires AC, with no DC bias, or it will travel to the endstop and wedge there overheating and distorting - if you want audio and not smoke the solution is to get an audio amplifier - there are commodity ICs that do the job.

Magician, your circuit is working perfectly! Thank you very much. Is there someway that I might be able to calculate mA output? (I didn't really understand your comment

Emitter follower will increase mA proportionally to h21.

MarkT, thank you for the help, because I'm only using this speaker for simple indicator sounds I was looking for a quick, cheap solution that I already had the equipment to do. Were I using the speaker for a more constant and elaborate purpose I would probably have looked into audio amplifiers as you suggested.

You are welcome. In short, circuit amplifies a current in h21+1 times, that is 1000+1 for TIP120 transistor.
Look more for theory on wiki:

Please, be advised that voltage at the output, approximately, Vout = Vin - 1.5V, or less than 3.5V, and consequently power is limited to V^2/R = 2.5W maximum for DC
(V^2/2R for AC), that should be o’k with 10W speaker. In order to get more power you can use another one (which is less safe, and as it noted above could turn your speaker in smoke and ashes with power source +12V )

Do you mean 2N2222A? Max current 0.6A (peak 0.8A), with 3.5V / 4 ohm = 0.88A it's in real danger. You should turn knob at the input no more than 50% (or use constant voltage divider 2:1)

This should clear things up.
Here is what my circuit looks like:

Do you mean 2N2222A?

Yes.

hfe for transistor is between 35 and 300. It's mean input resistance of the darlington approx. is: hfe x hfe x R = 35 x 35 x 4 = 4900 minimum or 300 x 300 x 4 = 360000 maximum, resistor 10 k in series can't control gain , and has no sense. And second problem with a transistor is total dissipation power = 0.5 W. Saturation voltage 1.5V puts a limit on current: I = P/V = 0.5/1.5 = 333 mA. You should find better transistor.

So what are the Ohm mA and V levels through my speaker? :s

All this are variables: hfe, mA, V with Gaussian distribution function.... In other words, only God knows, but you should feel lucky if it is still working. :)

hahaha thanks! yea I just unhooked my speaker (it's not 100% necessary anyways) Thankfully my I/O pin didn't get fried!