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Standalone Arduino + Wave Shield + Ampli (20 hrs autonomy) ♫
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Standalone Arduino + Wave Shield + Ampli (20 hrs autonomy) ♫

by Math on Mon Mar 02, 2009 2:55 am

Hi to everyone!

I'm currently working on a project involving the realization of a stand-alone sound reproductor.
Sine I'm not really an expert I thought to ask here for some advices.

So, this sound reproductor:
- is rechargeable
- has to be loud enough (more or less like a violin...)
- ...should fit in a 4/4 violin :)
- needs an overall autonomy of more or less 20 hours (3-4 of which emitting "loud" sound)

Please see in the below attached image a simple diagram of what I thought could work.

For its form factor, price and mAh rating: YUASA NP 7-6 (7000 mAh, 6V) (datasheets).
I would charge this one with a proper Lead "wall wart" battery charger.
(Other option: NiCd / NiMh battery pack + proper charger?? :\ )
Also: good thing to interrupt the circuit to the BBC while charging or it's irrelevant? (see drawing)

Buck-Boost converter (BBC) (for maximum possible duration... me thinks!)
After checking DC-DC Step-up and Step-down converters I've finally met this nice BBC option.
I would use a circuit based on the Maxim's ICs MAX710 or on the MAX711 (like in the Minty Boost IIRC).
In this way I would have constant 5V from a source varying between 11 V down to 1.8 V... \o/ (right? better options??)

Arduino + Wave Shield
Ok, you know these. The only doubt I have is: the above BBC is outputting (more or less) a round 5V, so the best (only?) option would be to avoid the 7805 on the Arduino. What would be the better way to do this?
a) USB "plug" input
b) Directly to the circuit's 5V line ?
Then, looking at the various specs I think that the supplied 5V from above would also suffice for the waveshield, right?

Reed Switch
This one will trigger the sound replay. I thought that a reed switch was a best choice in comparison with a hall effect sensor (I will be using this one (10-20 Amp Turns sensitivity) in combination with this neodymium magnet), I never had any experience with these things but I suppose it should do the job (magnet-switch distance would range from 6 cm down to 1 cm).

LM368-based Amplifier
As I previously said, the device should be loud enough to be heared well at let's say 3-4 m, in a wide closed space.
So, while hunting for cheap / straightforward amplification circuits, I came across these 2 schematics:
The nice thing is that while being both extra-simple, they're also fine with the already available 0 .. +5V and it also seems they will provide enough horse-power to the output speaker :D
The bad thing would be maybe the current draw... it's also true that for this project the Wave Shield would emit sound only for about 15-20% of the time (so making the equivalent of circa 3-4 continuous "loud" hours)

The speaker will be enclosed into the violin (trying to avoid acoustic short circuit).
I'm just undecided between a 4 Ohm or a 8 Ohm speaker.
A 4 Ohm one would sound louder but would also draw more current, right?

So many questions... any advice is warmly welcome!

Thanks in advance

Sketch for the standalone Arduino+Waveshield et al.
drawing.png (122.49 KiB) Viewed 1141 times
Posts: 1
Joined: Mon Mar 02, 2009 1:22 am

Please be positive and constructive with your questions and comments.