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# Have music control a device with sine wave and frequency? Answered

Whilst I was using  a TENS unit (electric muscle stimulator) and was messing with the frequency and pulse width controls, I thought to myself, "What if I would redesign this device, so that I could plug it into my mp3 player and it control the frequency and pulse width so I could literally feel the music?" After long though, and looking to see if such a device existed (None that I could find.) I came up with nothing. Now my question is, how could I design such a device that would take in standard audio, and give a pulse width and frequency output? I would assume I would use a pulse width modulator (PWM) for the first part, but what about the frequency? And how would I make this as one unit? I am a complete novice at sine waves, frequency, audio, and things in that area, and I find the best way to learn is do a project involving it. So would anyone have an idea how such a device could be designed? Link, circuit diagrams, and tips are all gladly excepted.

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## 14 Replies

Actually the Tens unit uses oscillators driving the voltage generators.

I would simply disconnect the oscillator wire and feed the audio of
your MP3 ( you may need to match impedance ) to the voltage generator.

Use the power control as a signal volume and the MP3 stereo can run both
of the Tens separate channels.

It should be possible to make a switch to go between the normal Tens and MP3.

I would imagine a deep monk ohm chant will give you a low freq shaking to
rival the best drugs on the streeet ;-)

RocketPenguin (author)2014-01-10

So, what you are saying is to first separate the two channels, and wire left sound for one as the input power source, and right sound for the other channels power source, correct? The issue is the device requires an initial 9VDC to power it, and audio output from a normal device doesn't go above 5.5v (Doubt it even gets that high, the battery of a standard mp3 player is 5.5v and i believe earbuds cant go above 4 volts without burning up...) This leaves me wondering, if i can manually control the Frequency and Pulse width with two knobs (I assume pots) then why couldnt i have the music control those instead? I do realize i could have input being the music, but why not it control those two instead? I would think it wouldnt be practical to have it as input voltage, considering thats where the main power is used (It would be like controlling an amp through the wall socket and no the audio jack) and if the music was injected as the main power, wouldnt the two knobs interfere with it?

iceng (author)2014-01-10

I have a Tens and used it, I am a EE and know what PWM is !!!

Do you ?

My point is, audio sounds are your ultimate frequency and PWM in one signal.

Use an audio transformer from Mouser Electronics to isolate and match impedances. There are many kinds of audio isolation matching transformers.

You could try using FETransistors, are you a skilled EE technician ?

You will need to experiment to match your ear-bud resistance.

This is instructables after all. The Voltage control is your built in Volume and Power in one control.

If you don't understand this, forget about anything from me and go another way.

RocketPenguin (author)2014-01-11

No, I am not an EE Technician, and do I know what PWM is, to a point. I have turned audio into a PWM signal before, using an arduino. Ear buds have different resistances depending on quality, and for this project ear buds have nothing to do with it, after all, I am getting my audio source from a computer or mp3 player, which would directly go to the unit. Yes, for volume the knob for each channel would be volume control. I do understand that audio sounds are my ultimate frequency, and that pwm is one signal. What I am thinking, is the audio would control the frequency, but also the pwm (for let's say like a beat of the music. Frequency is only one half of the device, what would I have the pulse width set to for music?) I honestly have no idea why I would need an audio transformer to match impedencies, what would I be matching it to??? I am no where near as smart or intelligent as you are, lack the knowledge on a lot of this, but I am willing and eager to learn and am doing some side studying on the topic. If it wouldn't be too much trouble to explain a few things, it would be greatly epriciated. Another thing, to control freq. And PW, the unit uses two variable ressistors. Wouldn't that be what I would have to control? The resistance? I don't know, though I would love to learn. If you do not have the time or patience to explain, well I am sorry for waisting you time in the first place.

steveastrouk (author)2014-01-11

Iceng is an Engineer, not a technician. Engineers design things, technicians build them.

iceng (author)2014-01-11

Lets start at one end. The ubiquitous Ear Bud !

In the end an ear bud is a tiny fine coil of wire acting on a diaphragm to create pressure air waves in proportion to electrical currents representing audio sounds for your ear drum.

Now different wire diameters with different number of turns makes for different ear piece impedances ie resistance coupled to fascinating mechanical acoustic designs and you have your subjective measure of product excellence..

But do remember this ear miniature speaker is in fact a Magnetic device. Which is half of a transformer by lacking another coil.

A transformer can take a low voltage and raise it higher at the secondary.

That is part of that impedance matching that Ive mentioned before.

AndrewT131 (author)2018-03-29

This device should do the job. You could use Frex and CHIamp as additional audio sources. http://spectrotek.com

I believe what you mean by PWM is a carrier wave is needed for standard TENS application. Read the Spectrotek site to learn more. He will sometimes sell the schematics.

FreX and CHI AMP can be found here. http://www.frex.com.au

I am interested in this also. Let me know if you make anything. I am disabled with little money for such things as this. I would like to be able to piece together something also.

Josehf Murchison (author)2014-01-10

If you want to feel the music a simple solenoid connected to the output of the MP3 player would enable you to feel the vibrations.

Now if you want to use the Tens like an equalizer and it does not have an input you are in for some serious rewiring.

Do you have a schematic of the circuitry?

RocketPenguin (author)2014-01-10

A TENS unit doesn't vibrate you or parts of your body, instead if feeds an electric pulse into your muscles making the contract and relax, making your body shake if on a too high of a voltage. And as in input, what do you mean? Yes, of course i would have to modify the unit to an extent, but would keep the part that increases the voltage to the safe levels needed for it to actually stimulate the muscles and not kill you. And about a schematic. I looked around on the web a little bit, and found making a TENS unit is actually very simple and does not require too many parts, though i would be worried about it, it being electricity fed into my body and i like living. I may just make a unit myself, it being much cheaper (A unit ranging in the \$80 range, and i am just a mere high school student who has no income, yet.) As for a schematic, if you look up TENS unit schematic, it will bring up dozens of variations of the device.

Josehf Murchison (author)2014-01-10

Oh I know what a Tens is they have been used on me in physiotherapy a
number of times for spinal injuries.

I don’t feel
them my muscles twitch and everything but I feel nothing when they are used on
me.

I feel
electrical shocks I tell if a small engines coil is working by running the spark
across my hand but I don’t feel a tens.

I would
go with the vibrators simply because I can feel that and they are safe compared
to electrocuting yourself.

Most of all you can feel high frequencies with
vibrators, a tens just sizes your muscles at a point.

You might
get base but at higher frequencies your muscles would just freeze.

RocketPenguin (author)2014-01-11

When I use a Tens, depending what I have the frequency and pwm set on it can feel as quick sudden jerks across my back, or it can feel as if I stuck two wires into a wall socket and touched the other ends to my back. The thing with a vibrator is they make noise, noise the ear can hear, while a tens doesn't. And plus, the tens electro pads are flat while a vibrator wouldn't be... About higher frequencies, I don't believe a tens unit can go high enough to do that.

Josehf Murchison (author)2014-01-11

If you go the way icing suggests which is probably the only way to go when you bypass the oscillators you will be receiving signals in the KHz.

This is beyond the neural electrical response of the human body.

At best you will perceive base and rhythm.

mpilchfamily (author)2014-01-09