paper speakers and LM358

Hello I am interested in making speakers with conductive paint and using a basic circuit to connect to an arduino uno or lilypad arduino. tutorial here: http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads I would like to amplify the sound from the speakers and was wondering if an op-amp such as the LM358 could be used for this purpose? JH

if an op-amp such as the LM358 could be used for this purpose

No that amplifier is a low power one. You need an audio amplifier that can handle the current but as you have not said how much current your home made speaker takes it is difficult to recommend an amplifier that is suitable.

Do you have a link to information about the speakers made with conductive paint?

What do you mean, amplify the sound -from- the speakers? Did you mean amplify and send it to the speakers?

Ah! Are you talking about painting a coil on paper using conductive paint, then holding it close to a magnet?

http://hlt.media.mit.edu/?p=1372

That is -really- low impedance, essentially a dead short. You'll really want to start with a very low voltage power supply with high current driver transistors. If you just want it to make a tone, use a high current transistor with a current limiting resistor in series with the paper speaker coil.

thanks for your replies, yes, I was looking at that page about paper speakers. I feel that maybe I lack enough experience in working with sound (had to look up the word impedance!) I would also like to make paper speakers that could be connected to an ipod (magnet being moved by someone and the speakers are connected to an ipod). Would this be difficult to do? For now I would like some advice on what is feasible with those simple speakers(for a beginner). Are there any tutorials that might show simple instructions on how to connect an ipod to homemade speakers?

Looking at the web page, they are using a TIP122 transistor. It's not a complete linear amplifier circuit, it's more of a "distortion generator" :D That's fine for the Arduino's PWM output and it will give you quite a bit of current, but probably not what you want for recorded voice or music. (But, maybe good-enough for a homemade speaker.)

The LM358 is NOT designed to drive speakers or headphones. [u]This page[/u] lists several low-power "power amplifier" chips (designed to drive speakers). Most of these should have over-current & over-temperature protection, so you won't fry the amp with a low-impedance (or unknown impedance) speaker.

A 4 to 10 Ohm resistor in series with the speaker would also protect the amplifier. (Impedance/resistance adds-up in series.) A series will reduce the power going to the speaker, but with so many unknowns it's hard to guess if that would be an issue.

Lack of experience is an excellent reason to go ahead with this. Best way to learn is by doing!

I'd go with an amplifier that can drive a very low impedance and as DVDdoug suggests, over-current and thermal protection and a resistor in series. If the amp can drive a 4 ohm speaker, use a 4 ohm resistor. If 8, use 8. You are trying to get the maximum current you can out of the amplifier.

I've been using the ada fruit wave shield to play music with arduino uno. If I were to use the paper speakers with this device how would I go about it? Sorry general question-but the speakers would be painted with a paint that has a high level of resistance(bare conductive -it can be painted on skin as well so it is not conducting much electricity).

Whether or not it can be painted on skin has nothing to do with its conductivity. What matters there is how much voltage is applied, and in -that- case, higher conductivity would be better because the same current would cause less voltage... it is a rather complex issue.

As to the wave shield, it is using two TL072 Op Amps in parallel. Not capable of much output. You may find that your paper speaker is barely audible, if at all. It is going to be -very- inefficient.

Your coil should be made so that it is barely larger in diameter than the magnet. Anything larger than that, it cuts the magnetic field when it is coming back and will make it quieter.

As part of a Mr Science thing I do, I've wound about 20 turns of 28 gauge enameled wire on a mousse can top, and have a very large supermagnet I use that just fits in it with a little room to spare. The cap is glued to a paper plate.

I use a boombox that puts out about 20W per channel and it can withstand a dead short at full volume. Even so, the paper speaker I've made is about as loud as a small transistor radio.

Your coil should be made so that it is barely larger in diameter than the magnet. Anything larger than that, it cuts the magnetic field when it is coming back and will make it quieter". So to have a larger speaker(because I am interested drawing and stencilling larger shapes) could I add one of the amplifiers that have been suggested in replies above to the shield-say on a bread board attached? Or must the speaker be part of a larger drawing?

I have found a recipe for conductive paint that is made with a reduction of copper sulfate and ascorbic acid which might be better for this project. It has less resistance and is nicer to paint with. thanks for your help

So to have a larger speaker(because I am interested drawing and stencilling larger shapes) could I add one of the amplifiers that have been suggested in replies above to the shield-say on a bread board attached? Or must the speaker be part of a larger drawing?

You should be able to plug the output from that Wave Shield into a more powerful amplifier.

I don't understand what you mean by "part of a larger drawing".

What I want is to have a painted speaker as an element of a drawing or stenciled design made with conductive paint. For this project the sound doesn't necessarily have to be great or even that loud, but I would like to use the wave shield + uno and possibly as you have suggested, the amplifier plugged into the output of the wave shield. So.. going on what I understood from your reply, the size of the painted speaker must be small but the sound can be amplified; I want the speaker to be larger in scale so I suppose I have to get a giant magnet! thanks again

It will help if the paper is large but stiff, supported only on the edges.