Does this circuit look correct

Hi i am trying to use an Arduino to control sound across different rooms of my house.

Here is the deign I came up with for switching the speakers on and off via a NPN Transistor. Can anyone see any obvious issues with it or can anyone provide any feedback (no pun intended).

Well - now I could be wrong, but I think in response to a DC signal, Q1 is only going to conduct in one direction, and since you are wanting to drive the speaker with an AC signal, half of your signal will be "chopped off"...

That might affect sound quality...

Hi, I think you would have problems with that.

Firstly, if you are using the same ground as the Arduino, you are going to end up half-wave rectifying your audio signal. Which will sound terrible.

Secondly, I think all the parts of your sound signal that fall below about 0.5V will clip to nothing. Which will make it sound even more terrible and mean that you can only play quite loud sounds (assuming 8 ohm speakers).

For a minimal component count, this is one situation where I might actually recommend using a relay. Especially if you are fairly new to electronics. Most relays, even 5V ones draw a bit too much for the Arduino output pin, so you will need to use a small transistor. Also don't forget the diode to suppress back emf.

Google driving a relay from Arduino / pic / ,icrocontroller, you will find lots of example circuits.

If you do try it, I would love to hear from you what it did sound like :-)

Snap ! simultaneous post !

Start here - also look up "transistor amplifier", "biasing", etc:

http://www.allaboutcircuits.com/vol_3/chpt_4/9.html

Now - it might be possible to set up a simple Class-B amplifier with a second inline NPN transistor to switch it on and off; but Class-B's aren't very efficient, and their fidelity isn't that great (ok for an intercom, not so good for music, unless your source is an old AM radio).

Another option would be to use an LM386 (or similar amp - there are better ones out there now) that has a "bypass" pin - to allow you to effectively mute a speaker; of course, all of these options (transistor amp, LM386, etc) require there to be a source of power at the speaker, unfortunately - there are ways around this, none of them easy to implement, though (one way, for instance, might be to use a CAT5/6 cable, so there is one ground return for audio and DC, and the other 7 lines are mixed signal and +VDC; selection is done via a data burst or tone, audio needs to have the DC bias removed, each speaker has a selectable amp controlled by a circuit, which may include a small microcontroller activating/deactivating the amp, etc - 7 speakers, one cable run).

Snap ! simultaneous post !

Relays would work ok; there might be some "crosstalk" and such, but that could be filtered out. The OP didn't say where the switching was to occur, though (central point in the house near an amp, or at each speaker controlled by a wall switch).

Actually, that last bit is how it is typically done - you have a distribution amp at your amplifier, wall switch/volume controls in each room with speaker(s). Lots of wiring, of course. Those wall switch/volume controls can sometimes also be centrally controlled (those kinds of installations are expensive, but may be cheaper than what you can homebrew).

Hi my first instinct was to use relays but I decide to see if it would be possible just using the transitory.

Just to expand a bit on what I am trying to accomplish. The idea is to have 1 arduino controlling 4 sets of speakers in diffident rooms. Pressing buttons on the controller (I plan to add a web interface at some point in the future) will turn off and on the output in diffident rooms.

The switching would take place at a central hub with about 4 relays on it. Each room will have its own stereo amp with volume controls I have the amps already so this is not a issue.

Thank you For your comments

If you want to be 'green' about it, why not use the relays or opto-isolated SCRs to switch the mains to each amp.

Depending on your amps, you might have to put up with the odd 'thump' but at least you are only making carbon when you need to.

Just a thought.

You know that never occurred to me. I build a relay controlled not long ago thats rated for UK mains. It could be easily adapted. Also I will give my original idea a try and see how bad/good it sounds.