Increase volume with external power via Uno not working as expected


Still relatively new to all this, but I think what I am trying to do is pretty basic. Using the toneMelody example on Arduino IDE software, I am wanting to make a 5" speaker bounce like a trampoline.

But regardless of what voltage I put through it, I do not get the loudness out as expected. Please find the images below.

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I am using:

5" speaker BUZ91A Mosfet to switch the current.

Not sure I totally understand the Ohms rule, but I thought the louder it would get is based on the voltage. Seems I was wrong. So I understanding I am missing a principle here but confused to which one!

Any help would be appreciated.



The BUZ91A MOSFET requires 10V gate drive.

You need a logic-level MOSFET if being controlled from a 5V Arduino.

You will be able to burn out the speaker then(!) Speakers are easily fried with DC current so keep an eye on that.

Thank you Mark, Would the below link be the correct one to really make it bounce:


You don’t need the pot. A single MOSFET is not a linear amplifier so the pot won’t work properly as a volume control, and you are more-likely to overheat the MOSFET.

Using the toneMelody example on Arduino IDE software,

You’ll probably have to go lower in frequency. The speaker has inertia… It will move enough to make sound at high frequencies but probably not enough to see. Try tone(31). That’s the lowest you can go with tone(). If that’s not low enough to see the speaker move, try the Blink Example. With a small speaker like that you won’t hear 31Hz (especially without a cabinet) but since it’s a square wave you will hear the harmonics.

Also try 5VDC directly from the power supply. You should see the speaker move when you connect and disconnect the power. (But don’t leave it connected too long.)

Not sure I totally understand the Ohms rule, but I thought the louder it would get is based on the voltage.

Yes. The volume depends on power (Watts) and frequency (and the efficiency of the speaker).

Ohm’s Law: Current (Amps) = Voltage/Resistance.

Power (Watts) = Voltage x Currnet

And with algebra you can derive:

Power (Watts) = Voltage2/Resistance

Power (Watts) = Current2 x Resistance

The DC resistance of a speaker is usually lower than the rated-nominal impedance.

The square wave is off half the time so you’re getting half the calculated power.

Speakers are rated for music. A 10 Watt amplifier that’s hitting 10W on the peaks is putting-out about 1W average. You can burn-out a “10W” speaker with constant 10W test-tones or 10W DC.

You need to give the speaker an AC signal to get the maximum cone movement. With just an on / off DC signal the cone will only move from the center position to either out or in depending on which way round you connect the signal. So to get the full extent of the possible movement you need to first send the current through it one way and then reverse the direction of the current and send it the other way.

Fortunately there are ready built ICs to do this, it is called an H-bridge. These are normally used for driving motors. However you can use a large audio amplifier if you want to move the cone with other movement profiles than just out and in alternatively.

I assume you are wanting to do this sort of thing, like a good friend of mine did for his PhD:- The Augmented Tonoscope/

A quick video is here And a search for "The Augmented Tonoscope" - under the videos tab will show more including his address to a conference on his project.

Here is an example of what I am trying to do:

This explains why I wanna see the speaker bounce :-)

Thanks for the video. So it looks like you will need a H-bridge after all. You will get twice the speaker movement for the same voltage.

What I have done, purely out of curiosity, is take a part an old AMP, and I think I took out the amplifier which I planned to use. However it is a little confusing.

I will take some photos of it and post it, because I am sure I could use that to boost the noise?

I have a duel H-Bridge, would this do what I need. It was for step-motors ?

I have a duel H-Bridge, would this do what I need.