# Wafer Vibrations

Discussion in 'General Electronics Discussion' started by Peter12, Mar 2, 2014.

1. ### Peter12

3
0
Mar 2, 2014
Hello every one,

I am working on a small project of creating vibrations by using wafer (speaker) to be connected discretely to an adjusted source of power and a variable currant. the transformer is AC one , and to adjust the power I will be using just a rheostat.
I didn't do any test yet, I was thinking if the sin waves can move the speaker to one direction when it's positive and the down the opposite direction when its negative, then what's left is to get the right values for not damaging the speaker in in order to get vibration system.

The AC transformer ( out put 0 to 120 VAC)

I am not sure if it going to work, but before buying the equipment I need your help guys.

Does any one worked or tested this kind of wiring?

Thank you,

Peter

2. ### Merlin3189

250
69
Aug 4, 2011
Vibrations in a speaker

If I understand you right, you want to power a speaker from an AC source and rheostsat.
Certainly you can do this, though 120V seems far too high to be sensible and you will get vibrations only at 50 Hz (or 60Hz depending where you are.) You'd be better off finding a low Voltage supply, say 3, 6, 9 or 12V AC, unless you are using a big speaker ("wafer" sounds to me like a very small speaker.)
If you have your speaker (wafer?) you need to know it's impedance and power rating, then you can calculate the current and the resistance needed from your rheostat.

Say you had an 8 Ohm, 5 Watt speaker, then
the maximum Voltage to apply is given from P = V^2 / R
so 5=V^2 / 8 so V^2 = 40 and Vmax = about 6.5V

or the maximum current from P = I^2 x R
5 = I^2 x 8 so I^2 = 0.625 and Imax = about 0.8 Amp

Then you know you could power this directly from a supply up to 6V, and if you used a 12V supply, you would need to drop at least 6V when drawing 0.8 Amp ie. about 8 Ohm.
If you tried to use a 120V supply, you'd need to drop 114V at 0.8 Amp which would need about 150 Ohm, BUT would be generating nearly 100 W of heat - and that's a big rheostat.

If your speaker is less than 5W (and "wafer" suggests it is) then your problems get even bigger. It helps if your speaker has a higher impedance, but 32 Ohm is the highest I've seen in common use and most modern speakers tend to be 8 Ohm or less.

I'm a bit puzzled as to why you want a speaker buzzing at 50Hz. Most people (well electronics & audio buffs) spend their time trying to stop speakers doing this!!
Perhaps the wafer is not the speaker, but a thin sheet of wood, metal or plastic that you want to cause to vibrate by using a speaker. Maybe to see standing wave patterns like a Chladni plate or to grow fascinating little flowers in cornstarch paste or to set up ripples in water or ???
In such cases you might find you want vibrations at other than 50Hz. So you might be better off building a very simple signal generator with an oscillator (even as simple as a 555 ) and an audio power amp (again a simple single chip with the required power rating, or, if you really don't care about the waveform, the 555 switching a big transistor.)

For me the bigger problem here is how you connect the speaker to the wafer so that you get an effective transfer of power. I think people might have more ideas about that if they had some more info about what you are trying to do.

Last edited: Mar 2, 2014
3. ### Peter12

3
0
Mar 2, 2014
Thank you very for the reply. I will be using variable AC transformer (the one I found is 0 to 120 VAC) and rheostat to vary the currant. I am assuming if I vary these two values I may vary the vibrations as well (in out of the wafer weak to stronger). I will not be using the wafer for any sound but it will be used for pharmaceutical machine, powder segregation. I will be using different size of wafer from small to big that's whey I chosen a variable transformer.
I think varying the frequency will better, that way I may get different speeds let say from 1 hz to 60 hz. But I am not an experienced builder of electronic circuits and probably will cost less and faster to build with just transformer and rheostat. I am open to suggestions and welcome any help if it easy to build such a system.

I need just to vibrate wafers (speakers) without destroying them, and it has be a constant wave in order to get the wanted result each time and same samples.

Thank you

4. ### duke37

5,364
769
Jan 9, 2011
There was a requirement for a low frequency oscillator here a few days ago, it was suggested to use an 8038? chip. Alternatively, there is a voltage controlled oscillator in a LM567.You could also use a cmos 4047 oscillator/divider.

Feed the ouput of the oscillator to an audio amplifier to drive your speakers. The amplifier will need to be large enough and will need to be DC coupled if you are going below 30Hz.

5. ### Peter12

3
0
Mar 2, 2014
Thank you Duke37. I appreciate your information.

Peter