Jump to content
Electronics-Lab.com Community

Electronic Stethoscope


t_ang4
 Share

Recommended Posts

Thank you Audioguru :), you have explained very well as usual ;), how I am to go about making these changes.

The quality of the sound file that I've posted didn't turn out as good as I hoped :(, I had to hold the microphone I use for my computer, next to the speaker from my digital video camera to record it to the computer :(, and I've also posted a pic of the device, one of the stethoscope heads I've made is much like the one in the pic.
%7Boption%7D

post-2744-14279142195087_thumb.jpg

heart_baby.zip

Link to comment
Share on other sites

  • Replies 388
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

Hi Dazza,
That's cool!  ;D
Your little rascal's heart is racing like mine does after running around the block.
It sounds like a frequency upshift circuit is used to convert the approx. 20Hz heartbeat sound up to a few hundred Hz.
About 15 years ago I designed a voice encryption circuit for boardroom wireless mics. It converted low frequencies to high frequencies and visa-versa. It would do the job but is fairly complex.

I found an article in Google where a doctor made his own electronic stethoscope with frequency upshifting: 

post-1706-14279142195697_thumb.gif

Link to comment
Share on other sites

Hi Audioguru :),

Ahh! I was on the right track in my earlier post, so it's called frequency upshifting :), I knew exactly what it was I wanted to try to do, but I didn't know what it was called ???.

So it's a difficult thing to do frequency upshifting :(, I've tried many google searches with different keywords, to first find out what it was called, then try to find some examples circuits, I should have better luck now ;).

What do you think of my idea of adding an extra stage, another TL072 or maybe more that way they could be dedicated to isolating Pacific frequencies that are all related to a Pacific sound, for example respitory sounds would be made up of many different frequencies, some of which would be the same as other sounds, so you would want to isolate as many sounds as possible related to only that of what you want to here, then these frequencies/sounds can be delivered to the  frequency upshifting stage then to the final amplifying stage, you did mention that it's not a good idea to use extra microphones, so would there be any problems with using just the one, that is ideally suited for this purpose, I guess it would be one that is ideally suited to respond to those specific frequencies, that is once you know what they are.

Now I am not looking to design a new high-tech device ;D, just one that will work as good as I can make it, to listen to my babies heartbeat 8).

If these extra stages will work the way I think they will (but I could be very wrong :-\) it would give a lot of flexibility, for example say there was a Pacific frequency/sound of the heartbeat that was the strongest loudest and it was also the strongest loudest frequency of the respiratory sounds, then the gain of that stage that is dedicated to that frequency could be adjusted accordingly (likely to be reduced), so it's still part of the combination of sounds introduced into the final stage. Also if you have isolated a sound of high frequency you wouldn't want to deliver that to the frequency upshifting stage with too much gain ;D.

Nice article Audioguru, very helpful.
Do you have any example circuits of frequency upshifting, that won't give me a fright :o ;D.

Just one more thing to add, the doctor said that the heartbeat sounded perfect, that is music to my ears 8).

Link to comment
Share on other sites

Hi Dazza,
You don't need to isolate many specific sound frequencies. As the doctor says in his article and are shown in 'scope pics in this thread, heartbeats are a pressure wave at a very low frequency, straining the lower limit of your hearing, microphones and he didn't mention the speakers or headphones. I remember hearing thump, thump of my unborn kids using just an ear.

To change the frequencies, you need a frequency mixer. I used an MC1496 multiplier IC with single-sideband-suppressed-carrier modulation in my voice encryption circuits.
Frequency mixing makes sum and difference frequencies and I had to filter the heck out of it to eliminate the sum frequencies. I used a switched-capacitor low-pass-filter IC as a very sharp filter.
The carrier frequency was 3580Hz, divided down from a cheap 3.58MHz colour TV quartz crystal. Your TV's use a little bit higher frequency. The clock for the switched-cap IC was 358KHz. It was easy to make the clock and divide-by-ten frequencies with a 74HC4060 and a CD4017 IC's.

Since my carrier was 3580Hz, 20Hz input resulted in 3560Hz output, way too high for your application. If you use a carrier of 358Hz, 20Hz input would give a 338Hz output, just about right. The output faithfully follows envelope changes in the original sound frequency.  ;D 

Link to comment
Share on other sites

Hi Audioguru,

I think I'd better do what I should have done before I started this project, find and read all the postings relating to this project, instead of just reading some of them ::).

Ok, I think I will keep well away from the frequency upshifting idea ;D, as it seems to be well beyond my capabilities :o, but still you have given me enough information, to at least look into it and try to understand how it works ;).

I'll have a play around/experiment, and I will post my findings.

Thanks again Audioguru :).

Link to comment
Share on other sites

Hi audioguru,

Your just being cheeky now, pulling my leg ;D ;D, are you mistaking me with somebody that actually knows what they're doing :o. sure why not if you do the easy part "design it" and put a big red circle on the schematics around the "on switch" so I know where it is ???, then I'll make the PCB and put it together, as long as you design it using components from the early Seventies, that way I'll have no problems finding components, I'll be able to get everything from my local Dick Smith Electronics shop ;D.


Actually I did come across a web site some time ago and I haven't been able to find it again, where someone was working on an ultrasound project, but I really don't think it would be a good idea using a home-made ultrasound device on an unborn child, sure it's only sound waves but I still wouldn't feel comfortable with it :-\

Link to comment
Share on other sites

Hi Dazza,
You're right, its best to keep any kind of radiation away from your unborn child.
I learned about Dick Smith Electronics, the surplus parts place, on another website. They sell used cars too, don't they?  ;D

On the other site are guys making circuits for their guitars. They break all the rules of electronics and post their schematics with weird names. They even post WAVE files of their results and some might convert your heartbeat sound into a fuzzy twang with vibrato and tremolo if you want. It would be cool to hear a heartbeat with flanging. A doctor would go nuts. ;D 

Link to comment
Share on other sites

Hi audioguru :),

I have come up with a circuit that might help me achieve what I am wanting :D, with the electronic stethoscope.

I have this idea working on the breadboard the way I want ;), and now I just need to connect them together, to see if it will work the way I want, but I'm having problems with this project that I found( http://sound.westhost.com/project43.htm ) which I thought would be good for powering both these projects.

I've attached pic's of the redrawn schematics and the PCB I designed for it, I'm fairly confident I didn't make an error, however it isn't working as expected, could it be that this project simply won't power the electronic stethoscope?, I did make some changes, I used a LM358? instead of a 1458 and I also removed C7 and C8 from the stethoscope.

When I connected this circuit to the electronic stethoscope to power it, I could barely hear my voice through the headphones when I spoke directly into the microphone, also when I adjusted the volume control to about half I could hear oscillation. When I read the authors description of how this project worked, I thought it would be ideal for powering the electronic stethoscope and my add-on circuit, but it looks as though I've gotten something wrong but I can't work out what :-\.

Any help would be very much appreciated.

Well it wouldn't surprise me one bit if Dick Smith did start selling used cars ;D.  At one time Dick Smith was the place to go for electronic enthusiast and pretty much the only place to get components, now they have just gone to the dogs >:(.

Yes it would be cool to hear a heartbeat with a bit of a twang to it ;D, in fact the circuit I am working on might just be able to do that, but first I need to try and get it to work for the purpose I intend to use it for 8), then I'll have some fun with it, to see what sounds I can make a heartbeat sound like ;D
http:
%7Boption%7D

post-2744-14279142201894_thumb.gif

post-2744-14279142202083_thumb.gif

Link to comment
Share on other sites

Hi Dazza,
The LM358 has a minimum output current rating of only 10mA, typically 20mA. If your LM386 in the electronic stethoscope is driving two paralleled 32 ohm earphones to full output, it would draw about 72mA plus a few more mA for the opamps. The LM358 is a low power device but an MC1458 is two 741 opamps which aren't much stronger.
Measure the voltage of the positive supply for the LM386. I think you will see the voltage collapse whenever the LM386 is trying to produce output.

Re-install C7 and C8, they are important to stop the circuit from motorboating. Just use two alkaline 9V batteries, but don't short them this time.  ;D 

Link to comment
Share on other sites

Hi Audioguru, steven

Audioguru, I have found that trial and error is the best way for me to learn electronics, I have had very little schooling and I struggle to get my head around the maths and theory :-\, in fact the only way I can write this post or any other, is with speech to text software.  I have found that first doing hands on projects and experimenting, makes it easier for me to understand the theory and maths ;).

The downside of using trial and error with this project is, trial and error = mistakes ;D = flat batteries :( = lets try that again :P = Oops that didn't work ::) = flat batteries :( = lets try something different :) = flat batteries :o = $$$ >:(.

This is my first audio project and my first project using a (+ - Gnd) and I'm learning a lot and very much enjoying it :), so I will definitely take on some more audio projects in the future, but before I take on my next audio project, I'll have to put together a decent PSU with + - Gnd.

But for now it would be nice to be able to power this project from my existing PSU ???, which is the 0-30 Vdc Stabilized Power Supply, from our project section 8).

Thanks steven, I'll check that out ;).

Link to comment
Share on other sites

:)dazza im suprised the top floor up stairs here hasent collapsed down onto the ground floor with the wieght of tons of electronics parts ive got upstairs , do you need any parts, its allso the main bedroom upstairs to  so i dont have far to go when i get out of bed  if i have any brain storm ideas to write down , my hydrogen generator still on hold pending on more ideas in the pipeline ,

Link to comment
Share on other sites

hi  Audioguru !!!!!
how r u ?for a long time later i come back :)
i finished the circuit and the matlab program to analyse the heart and respitory sounds.thank god :) anyway now i want to add a trnasmitter and receiver circuit because the cables really annoying hehe anyway what u suggest? i am searching for a simple, stable, and if possible without a needage of antenna hehe
do i want  so much things . i know i should write theese in another topic.but i want to get ur opinion . thanx
very very speciaal regards
ciaooooooooo

Link to comment
Share on other sites

Hi Hakyman, welcome back. ;D
You can purchase a cheap wireless link that is made for a wireless mouse and similar stuff.
You probably must modify them with bigger coupling capacitors to get very low heart frequencies.
It is complicated to make a stable transmitter and receiver.

Link to comment
Share on other sites

Guest Alun

Yes you could have a go with the transmitter discused here: http://www.electronics-lab.com/forum/index.php?topic=2814.0 but you will still need an antenna of some description, the reciever is simple a normal FM radio will do.

Link to comment
Share on other sites

hi guys thanx for the replies
audioguru could pls make it some clear  cause i dont see ever a mouse kit with rf i only use IR kits. and do u know a link have some schematics without a needage of antenna of transmitter. u can write to the link to alun gave at  above where u discuss about transmitters . thanx very much
very very best regards

Link to comment
Share on other sites

  • 1 month later...

Hi, I'm a new one here. I think what u're doing here can be more useful if you always make some update. I've question to ask.
1. How do you can define which filter you want to use to measure is it heart sound or lung sound or other sound of the body? Heart, lung, ang other body-sound have different frequencies, what are they?
2. How much gain do you use in this schematic? And if I want to have gain 25x, which part should I change?
3. If I want to have a display and a microcontroller at the output, is it possible and how?
Thank you. I appreciate it if you can send your answer directly to my e-mail address, [email protected], thank you.

Link to comment
Share on other sites

Hi E,
Welcome to our forum. ;D
From the tests that I have made, body sounds are like this:
1) Heart. An extremely low frequency DC pulse, sometimes modulated at about 25Hz.
2) Lung. Normal breathing and athsma squeaking is from about 300Hz to about 10kHz.
3) Blood flow. Probably also from 300Hz to 10kHz but my tests didn't have enough gain to hear it.

The project states the gain of its stages here:
http://www.electronics-lab.com/projects/science/019/index.html

You can't just pick a gain of 25 at random. The gain must match the amount of sound level and cannot be too high or the output stage will be noisy and distorted.
The project has a reasonable amount of gain that can be reduced with its volume control when required.

The project's output can be rectified and attenuated to match the input requirements of the ADC of a microcontroller. ;D

Link to comment
Share on other sites

  • 3 weeks later...

hi audioguru!!!!!

can you help me please improve this electronic stethoscope. i just want to make this elec-stetho to make it digital...

i want to connect a pulse counter on the bi-color LED, so that it will count the blinks of one LED. the counter will diplay the counted pulse on an 7-segment LED display. i also want to put a 60-seconds timed switch at the entrance of the pulse counter. this means it will stop the counting after 60-seconds to get the accurate heart rate.

next time i will attached my circuit. i dont knw how to edit the pic, coz were using redhat instead of microsoft word. thankss...

hope you can put attention on this....
any reaction are highly appreciated.....

----xoy------

Link to comment
Share on other sites

Hi Xoy,
For my Electronic Stethoscope-2 project, people have said and my tests have shown that the LED flickers with some hearbeats. This will give too many pulses to your counter. Therefore the circuit needs an integrator (very low frequency low-pass filter) to feed the LED driver that feeds the counter.
If you don't need audio output then the existing lowpass filter can be set to a lower frequency by increasing the values of its C3 and C4 and also increasing the values of its R5 and R6.
If you do need the audio then another lowpass filter can be made like the U1b stage, with the values increased.

Maybe it would be best to time the pulses for only 6 seconds and shift the decimal point in the display to indicate pulses per minute.

I use Microsoft Paint to edit all pics. It is much easier than Microsoft Word. ;D

Link to comment
Share on other sites

hi audioguru!!

tnx!!

maybe thats a good idea..

first, i have to ask.. does my idea really possible to make this digital?

does it mean i have to put another U1b stage. where should i place it?
another prolblem i have encounterd here is, the timer. for now i want to buy a kit of switch timer, but if you have one circuit of it , please post.
sorry,, but i dont iunderstand about that 6 seconds timer...


tnx!!!!

-------xoy-------

Link to comment
Share on other sites


first, i have to ask.. does my idea really possible to make this digital?

Sure, if there isn't any friction noises then your idea will allow this project to display heatbeat rate.

does it mean i have to put another U1b stage.

Yes if you still need its audio output.

where should i place it?

The new R5 will connect to the exising pin 7 of U1b. Then U4 connects to its output. The U4 circuit will need to be changed so that its output doesn't exceed +5V and doesn't go negative.

another prolblem i have encounterd here is, the timer. for now i want to buy a kit of switch timer, but if you have one circuit of it , please post.

Use any timer circuit.

sorry,, but i dont iunderstand about that 6 seconds timer...

You can count pulses for a full minute, or count pulses for only 6 seconds then add a zero the the number counted for the results in one full minute. For example, a heartbeat rate of 100 beats per minute will be counted as 10 in 6 seconds. Adding a zero at the end results in 100. ;D
Link to comment
Share on other sites

tnx audioguru!!!!

now i can start this....
i will notify you anytime for any improvements, problems, or anything...

i will use a an IC voltage regulator having an output of 5V.

wait.. i dont know how to trigger a switch using a timer to switch off the entrance input of the counter. i mean a timed switch...

i have my circuit to be.. but i can't upload it here using the bmp or paint..

thank you so much!!!

----xoy----

Link to comment
Share on other sites

Hi Xoy,
Silicon Chip magazine has a heartrate monitor project. They use a sensor that detects blood motion in the skin with an LED and optosensor. They use a PIC to do the counting and drive to a 3-digit LED display. You can see the entire project for free if you enter into a Google search, Silicon Chip Heartmate. In Australia and New Zealand, kits might be available with the PIC already programmed.

The output of your modified Electronic Stethoscope-2 circuit should be able to drive its counter easily. ;D

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share


×
  • Create New...