Help with connecting arduino to speakers

Thread Starter

Garurumon

Joined Mar 17, 2013
99
Hi.

I'm trying to build an Arduino step sequencer, and I finished all the hardware work except the sound output block. I'm not sure which way should I go, so I was hoping that someone could help me.

I came up with this so far:

sema.jpg

It consists of a few schemes I found online and modified to my needs, but I don't know whether those modifications are good. I'm also sceptical about my calculations.

The basic idea is to choose between the speaker that's in the project box, and line level output, with dual volume pot to control volumes on each of those.

The main concern I have is the capacitor people use when communicating with audio amps, like in the lower part of the scheme. Will the combination of back-EMF diode, no capacitor in series with speaker and "DC" square wave on the internal speaker make it sound much different than the sound I'll get from external speakers once I hook them onto the jack?

Also, is this the correct way of regulating the volume? And are there any more flaws in the schematic I drew?

Thanks in advance!
Miloš
 

ErnieM

Joined Apr 24, 2011
7,993
I have done something similar to your top drawing. As the transistor is either on or off the column control will not work. I did not use that diode, though I do believe I did have the series resistor.

The bottom drawing has an extra cap to ground. Leave that out, it forms a low pass filter which by the numbers will kill any audible signal you are trying to pass.
 

Thread Starter

Garurumon

Joined Mar 17, 2013
99
But I thought a transistor is a current device..? If the speaker's maximum current is 5V/(18+8)Ohm=192mA, and I turn the transistor to pass lets say 50mA, it would limit the current, and then a weaker pulse would go through the speaker, thus making a quieter sound, right?
 

ErnieM

Joined Apr 24, 2011
7,993
But you are not controlling the transistor current with that set up, best you can do is turn it on and off. You may find a very small band where the sound changes rapidly from none to all, but that is not the droids you are looking for.
 
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