Audio Signal to Control Electromagnet

Hi,
I'm a total newbie, so I have a project where I want to manipulate some ferrofluid with an electromagnet using an audio input (from say an iPhone). My initial thoughts was to have say 3 band passes corresponding to 3 electromagnets so you can see the individual elements of the song (such as bass ext).

I was hoping you guys could point me in the right direction in what to read up on how I can get this project rolling.

Like I said total newbie, had some experience with circuits from A level physics but thats about it!!

Many Thanks!
James

I have never seen ferrofluid move. Maybe a DC electromagnet can lift some clumps of it then gravity can lower them. Since music is AC then you would need to rectify and filter it then drive a power stage that drives the electromagnet.
I do not think more than one group of frequencies will work.

Are speakers themselves not electromagnets?, would it not be possible to do a speaker cross over type circuit and feed each output to the corresponding electromagnet. I will need more power than what any output could supply so i would have to have "boost" the power with a main input somewhere in the circuit.

At present low frequency Audio vibrators are available. Do you wish to do similar things?

What is your idea about manipulation ferrofluid with magnetic field?

Ferrofluid is used in speakers to improve their efficiency.

Well essentially you know the water speakers , I want to swap out the water with ferrofluid and create visuals in sync with the song using a mag field to control it.

I looked in Google for Water Speakers and found this You-Tube video showing them: https://www.youtube.com/watch?v=r9ZVrDmJo2s
Jets of water are squirted upward to the beat of the music. I could not find an article of how they work or a project to make them.
Maybe they use a little waterproof speaker to push water through tiny jets.

Ferrofluid has nothing to do with it. Ferrofluid is a thick oil with ferrous material in it and is attracted to a magnet. It is used in a tweeter speaker to conduct heat and damp resonances because the very strong magnet in a speaker holds the ferrofluid there.

The water speaker mechanically and quickly pushes water upward. But ferrofluid is not pushed by anything, instead it is simply slowly attracted to a magnet or an electromagnet.

Sorry audioguru, I want a to create a circuit which will pulse an electromagnet in sync with a music track played from say an Iphone. My water speaker was an analogy for what I will be using it for

jamd said:

Sorry audioguru, I want a to create a circuit which will pulse an electromagnet in sync with a music track played from say an Iphone. My water speaker was an analogy for what I will be using it for

Click to expand...

Again, you forgot to say what you want the electromagnet to do.
An electromagnet is simply a coil with an iron core. With DC (not audio which is AC) it can attract or repel a magnet or another electromagnet.
An electromagnet with a moving iron (that it can pull) or moving magnet (that it can push or pull) as its core can be a solenoid when powered with DC.

I me sure you can create an AC electromagnet? It's poles will switch when the current reverses and because ferrofluid is a induced magnetic material it will be attracted to the electromagnet regardless of the polarity. Essentially I want an electromagnet above the ferrofluid so when there is say heavy bass in a track the ferrofluid is pulled up towards the magnet on each beat and then turned of to allow the fluid to fall and then on another beat it being pulled up... Ect) hope this helps!!

Many thanks!!!

If you made a very strong electromagnet then maybe it can pull a clump of ferrofluid up maybe 1cm or less, then when the electromagnet is turned off the ferrofluid falls due to gravity. I hear that ferrofluid is fairly thick so it will move slowly. The movement will be VERY slow when the electromagnet is 1cm away then it will move faster (but still fairly slowly) when it gets closer to the electromagnet.
Where can you buy ferrofluid or will you make it yourself?

DC bias and amplify the AC signal and make sure that output is always positive, now supply the this voltage to electromagnet. for better results use sound of lower frequency.

An interesting thing about ferrofluid is the shapes it makes under the influence of a magnetic field. If you put a few electromagnets under some ferro fluid, you should be able to get the patterns to change and move around.

Alternatively, if you put some ferrofluid in a container filled with a water-based solution of similar density, then the ferrofluid will become effectively weightless and be much easier to move around with magnetic fields. I suspect the best you could hope for is slowly moving blobs, or something like a lava lamp. I can't think of a way to make a column of ferrofluid jump up and down though.

Electromagnets are inductive loads. If their Henry value is large, then they will not conduct very much current at audio frequencies. Hence I believe you should pulse them with DC.

You can filter an audio range, then use a peak detector to create DC pulses, which are amplified and applied to a transistor. The pulse lasts through several cycles of the original frequency.

Simulation showing how this would work for the bass frequencies:



I guessed at specs for the electromagnet. It looked to me as though 1.65 A and 30 mH provide waveforms that are workable.

BradtheRad said:

Electromagnets are inductive loads. If their Henry value is large, then they will not conduct very much current at audio frequencies. Hence I believe you should pulse them with DC.

You can filter an audio range, then use a peak detector to create DC pulses, which are amplified and applied to a transistor. The pulse lasts through several cycles of the original frequency.

Simulation showing how this would work for the bass frequencies:



I guessed at specs for the electromagnet. It looked to me as though 1.65 A and 30 mH provide waveforms that are workable.

Click to expand...

Hi Brad,
First of thanks very much for the design!!, is it possible if could you please explain how the circuit works and how i could adapt it for different frequencies and electromagnet strengths.

Many Thanks!

jamd said:

Hi Brad,
First of thanks very much for the design!!, is it possible if could you please explain how the circuit works and how i could adapt it for different frequencies and electromagnet strengths.

Click to expand...

Your project is like the visual display on a graphic equalizer. You split up an audio signal into several frequency bands, and you display the intensity within each band by means of led's, or, the motion of ferrofluid.

Look at projects for graphic equalizers to see how to make the bandpass filters. Each band can be extracted by one op amp and a couple of capacitors and resistors.

The peak detector holds the high point of a waveform. You must adjust RC values to obtain proper performance.

My simulation uses the op amp as a comparator. I put a potentiometer at the inverting input, to select a threshold for activating the electromagnet. Notice that by selecting a high threshold, you narrow the bandwidth of response.

The op amp must provide sufficient bias current. It must turn on the transistor sufficiently to activate the electromagnet. Unless you want to use mosfets instead of transistors, which is fine. However mosfets may be susceptible to voltage spikes from the electromagnets being switched off.

It is conceivable that two functions can be combined in one op amp. Example, the filter and peak detector. This will require some more research.

Ferro fluid is shown on videos in Google. Its oil s NOT thick as I thought, instead it can be kerosene which is thicker than water but is thinner than liquid honey.
Most videos show it in a glass bottle with an extremely strong tiny magnet moved around on the outside and the ferro fluid follows the magnet around on the inside very close to each other because the glass is thin.
The distance between the magnet and the ferro fluid is very small.

The ferro fluid is attracted to a magnet. I think you want to repel the ferro fluid which is not possible.