Electronic Stethoscope - New Design

Use the low f heartbeat audio signal to modulate a whitish noise source and its more clearly audible. You can also use a crystal earpiece then, to reduce i even further.

NT

NT That's a very interesting idea of yours...Have you seen it done before? jb

I really cant remember. Midrange frequencies are far more audible than heartbeat plus harmonics.

NT

Yes, I get it. Heart sounds are very low frequency. lub lub. Would it make sense to use a tone? One problem is heart murmurs sound like white noise - whoosh woosh. Perhaps analyze the sounds and convert to characteristic frequencies?

Say the main lub becomes 400 cycles with +/- 10% ..

and other stroke changes f - with the murmur a high frequency.

This would catch on, as docs find heart sounds difficult to interpret. esp MA's etc/\.

Yes, maybe - VCO from a 4046. Easy enough thing to try.

It wouldn't catch that though.

Thanks, but this misses the point a bit. I want to hear the heartbeat, not modulation.

Can anyone help?

Mark Harris

Not if you pose the question in the way that you have.

Your ears are really not sensitive to 0.8 to 4Hz (and if your heart is above 240 beats per minute you will have other problems).

What you hear by merely amplifying it will be the harmonics off the narrow fast power stroke but only then with some difficulty since most of the power is still below 60Hz. If you use the amplitude of the heartbeat signal to modulate some audio noise then you have something you can hear with the intensity of the noise representing the heartbeat.

I'd have thought the design you showed ought to work if made correctly although the hum levels might be a bit annoying.

On a sunny day (Fri, 02 May 2014 17:02:28 +1000) it happened snipped-for-privacy@comprodex.com wrote in :

Well, I have never dunnit , but if you go to ebay.com and type sthetoscope in the search window, I already see one for 4 dollars and 75 cents.

Being simplistic about it, how about fitting the electret or any other mike in the ear piece part? The other thing that occured to me, in the old days we had throat mikes, military stuff, some dynamic mijke around your neck. maybe tie one around your chest, bit of extra low gain? Dunno if that would work. But you never lose on the 4$75 investment I think. You could use your pulse (hand vains) and modulate something (red LED light intensity, LED + photocell, your finger in between, low frequency amplification, I can think of a thousand ways.

Electric skin voltage changes at heart position?

Someone once told me she had a heart valve replaced (by some artificial one) and could hear it clicking. In that case magnetic sensors could come into play ;-)

When I do a lot of physical excercise I sometimes can hear my heartbeat without any help from instruments.

So jump up and down a bit or try to make a new 100 meter record for a stronger signal with your electret?[1] [1] disclaimer: if you die from it, you shouldnothavedoneit.

and on and on

On a sunny day (Fri, 02 May 2014 08:38:01 +0100) it happened Martin Brown wrote in :

This is actully not correct, try poking your finger very slowly in and out your ear. The secret is in a good dynamic earpiece, or the 'tube' that conducts air pressure changes in a real stethoscope.

I have a 200$ ADC stethesoscope, and getting the low frequency into the mike seems to be important. You have to have good sound conduction, i'm not sure of the exact mechanics. The mike surface on this device is hard shell. Then a decent low frequency audio type amp, afaict. This is not rocket science electronically, and I suspect the problem is mike pickup and earphone transmission. (My adc uses an air column to the ear. )

VCO - let's see - why wouldn't it catch the higher frequencies? Out of lock range? It's an interesting idea.

No it wouldn't catch on. Been there. Have the T-Shirt.

Docs are trained in pattern recognition. Excell at it. They also train using a STETHOSCOPE made of diaphragm, tubes, and ear pipes. The sounds bouncing around inside that acoustical structure are a daunting task to duplicate electronically. In that combined training docs EXPECT to have all those nuances of artifacts added to the heart sounds. Calling your 'heart sound monitoring' electronics a stethoscope in no way makes it a stethoscope. It is a heart sound monitoring device.

Enjoy the project, but don't envision a way to have it replace the non-electronic version.

I think the point is that I want to hear what I could hear if I could put my ear up against my chest. I suspect that would be a short-lived experience, hence the electronics.

Unfortunately, the medical versions start at around $300. Hence the DIY electronics, which, by the way, is not for medical use.

Mark Harris

Here is a relevant article.

It looks like a good quality electret mic in a circular housing filled with resin. I am wondering what the purpose of the latter is and how it would improve conduction. Any ideas?

It appears that medical stethoscope heads consist of a flexible diaphram.

Here we see construction of a "proper" sensing head. The diaphram pushes air at the mic. IOW the mic does not pick up much of anything on its own. I am thinking condom stretched over a plastic tube.

Here they put a magnet on the diaphram.

Ditto here. Some pre- amp circuits at the bottom of the page.

Or perhaps this piezo mic would work without a diaphram?

With regard to the amp, the March issue of EPE has an infrasound amp project. This might be worth looking into.

I think I am getting the hang of it.

Mark Harris

All you need then is a high gain low frequency opamp circuit. Take a standard audio one and replace any coupling caps with ones 10x the size and you're there. Add a transistor pair on the output to give enough current.

NT

Any white noise components that are approaching the frequency of the audio from the VCO won't have much effect on the tone - but perhaps it'll make it waver a little in a way the ear could detect.

We use a VCO attached to the signal strength of a radio receiver to hunt for the strongest signal in direction-finding competition - we call it "whoopee mode". The ear is much more sensitive to pitch than to loudness.

snippety snip

Your thoughts well taken. Please allow me to differ on some points. Yes, I had the same mind-track about the essential conservatism of docs and their training. But consider another market: the 'people-at-large' monitoring their own health. This has been detailed in "The Creative Destruction of Medicine," Eric Topol md. An IBM main-frame did not have a user friendly UI, but the PC had to. It may be the same for heart monitoring. Rarely have new products recruited from within an established user base - you wouldn't sell the automobile to a horse-and-buggy company, or the airplane to Pullman Railroad Co. Electronic blood pressure monitors are replacing the cuff variety, and it is possible that heart monitoring could take a similar course. It may not be a "killer app," but the terrain of entrenched users is standard. I do pattern recognition recognition myself, and if the world's best cardiology diagnostician has his expertise ensconced in a neural net (easy), then suddenly a way is there to put the world's best before any consumer. QED disruption.

jb

"If you subtract the killings, DC has a low crime rate." - Mayor Berry, DC.

You could always have 3 modes: audio, hiss modulation, VCO

NT

"snippety snip"??!! LOL!

It always amazed me the standard comment 'lamented' by doctors was that patients didn't have interest in their helath care, didn't ask questions, etc etc. Yet when asked questions, too many doctors bristled, talked down to patients or worse, purposely over them, and really became incensed if a patient asked for second opinion. Well, one reaps what they sow. Now with health care cost out of control, and a population of intelligent people, the obvious has happened, there is a new market for viable health care products. I stand corrected. Point WELL taken. I forgot that when any industry demands that all go through them and then does not allow much to go through them that people will always look for, and find, alternatives. Following the adage of "get out of the way if you're not going to help".

Why not? Good health monitors can't hurt. Now let's work on direct neural excitation for control and bio-feedback, eh?