Electronic Stethoscope

[TriGeminal]

I soldered the circuit on a veroboard .. it didn't work (cause bad joints mainly) .. anyway I'm not going to solder anything again after I was ill for 2 weeks cause of the toxic fumes

I'll try again with the breadboard circuit ... but I'm thinking to simplify the circuit .. I mean I'd like to give my computer a chance in amplification, so I'd like to know what is the simplest circuit attached to the MIC that makes sounds reach my computer?

I can use many programs to amplify the sound, just a matter of time

 

[ante1]

What kind of solder do you use, must be some old extreme stuff. Throw it away if it makes you sick and buy the new lead-free solder instead. If you got sick for two weeks from this is very serious, are you sure it wasn’t a bad pizza or something else?

 

[TriGeminal]

What kind of solder do you use, must be some old extreme stuff.

I just bought a solder, which I guess had a large percent of lead .. even lead free solders can be more dangerous than solders that have lead!

I used another type, which had low amount of lead .. it was better, but same case, I had a weak respiratory system for days ..

When I was 6 years old I was used to use that type of solders and never had a problem, so I guess it's the place I solder .. it's not highly ventilated

Anyway, I'll be making a subdomain for that stethoscope, with shots and videos of every step in addition of medical hazards (cause we are medical students ) ..

 

[MP1]

Mostly what you are inhaling is the burning flux from the core of the solder. Here is a link to a MSDS safety data sheet.

http://www.ee.ryerson.ca/~jkoch/MSDS_Sheets/msds%20r244l%20sn63pb37%20us%20(03oct03).pdf

You should look for the specific MSDS for your solder product. Since you are a medical student, I am sure you will appreciate the information in this MSDS sheet and the safety precautions that should be taken when soldering. Never breath the fumes. If you find this to be impossible, invest in one of the many products on the market that extract the smoke from your work station.

MP

 

[TriGeminal]

Thank you MP, much appreciated

 

[solycutema]

heyz...

im currently working on my final year project.... it wld be really helpful if anyone cld tell me which is the finalised circuit that i shld follow......something that will work... is it the stethoscope 2 that audioguru posted?

and.. if i wld like to connect the entire circuit to the computer... which means i do not use a headphone but to play the sound straight through the com.. how do i go about it? wat jack do i need to use?

thanx....

 

[audioguru2]

Hi Soly,
Welcome to our forum. ;D
The headphones output of the Electronic Stethoscope-2 project can be connected to the Line Input of a computer by using whatever plug that fits your computer. If the computer doesn't have a Line Input but has only a Microphone Input jack then an attenuator must be made with a couple of resistors.

 

[Evixfel]

hi audioguru,

i am a biomedical engineer student working on a project on heartbeat sensor ive to build an application that can store the bpm of a patient...i plan to use a mod 60 counter as timer can u give me an idea of how do i store the heartbeat pulses? thx

uhm need a reply urgently :\

ill try to post my sensor circuit

 

[audioguru2]

Hi Evix,
You want to store the BPM number, not record all the pulses of heatbeats.

 

[Evixfel]

YES ur right man!

may i know wat circuit can i use to do that?

thx

 

[audioguru2]

Store the BPM number in a memory chip.

 

[germil]

Can someone please post a .jpg or pdf of a pcb ??? ? Iam newby and have some problems vith making a pcb design.

 

[audioguru2]

Our member, Con, made this excellent pcb design for the corrected and improved 2nd version of the Electronic Stethoscope-2 project:

View attachment 39529

 

[priyank1]

Hello Everyone.

This is my fist message to the group. I am currently workin on builiding a blood pressure monitor as my final year project. For the first sem i had used oscillometric method to measure the blood pressure. Luckly i was successfull in doing that...and got very good marks for that... 

for my second semester, I am now working on auscultatory method, and task is to capture Korotkoff Sound(Acoustic sounds from radial artery) and display the waveform on PC..project is exactly similar to Electronic Stethoscope...

I am currently going through 24 pages of discussion on the forum, trust me there are so many different circuits and suggestions ....well ill have few sleepless nights but ill try figure it out...

let me know if anyone wannts my report for oscillometric blood pressure monitor method...

ill keep u guys posted...WISH ME LUCK! ;D

pri

 

[audioguru2]

Hi Priyank,
Welcome to our forum. ;D
I fixed problems with the original Electronic Stethoscope project. My Electronic Stethoscope-2 project uses common cheap parts and is simple to make. Why don't you try it?
http://www.electronics-lab.com/projects/science/019/index.html

 

[priyank1]

G'day guys...

Hi audioguru, hello everyone...

As per ur suggestion i will try with circuit2. I was getting bit confused with so many circuits flying around in this forum..iv got test this week but i am confident that by next monday i should be able to breadboard the circuit ...i will keep u guys posted.

Audioguru i appreciate ur help. ..

pri

 

[priyank1]

Hey Guys..hi audio guru ;D

Iv just completed my tests for this week. last night i was simulating the circuit#2, i have simulated exactly according to ur modified circuit..i.e circuit#2. The only difference was during simulations i have used LM741 instead of lm386. I provided a sinewave signal of 10mv,10hz. The ouput which i got from the circuit(U5 at R15 of ur circuit diagram) was a sqaure wave with a amplitude of around 10-12 volts.

I am not sure if that is the output which i should be getting, i feel the output is clipping and thats the reason im getting bit distorted sqaure wave. Following is the picture of my simulated circuit and the output which i get.

please find attached screen shots of the simulated circuit and the transient response....(files are *.jpg files)....if u wannt i can also give all the dc opearting points of the simulated circuit. i am intending to start breadboarding the circuit from monday..before i do that i wannt to make sure i get everything correct on the simulations...

cheers
priyank

View attachment 39686

View attachment 39687

 

[audioguru2]

Your 741 opamp at the output doesn't have any negative feedback and therefore has a voltage gain of about 200,000. The LM386 that it is supposed to be has built-in negative feedback and therefore has a voltage gain of only 20. The gain of the 741 opamp is 10,000 times too high, sure it will clip.

The 741 won't work properly with its inputs DC at its negative supply (ground) but an LM386 is designed to work that way.

Your circuit has C3 connected to the wrong place, messing up the lowpass filter.

Fix C3, add negative feedback to the 741 opamp so its voltage gain is 20 and disconnect its negative supply pin 4 from ground and connect it to -9V instead. Then the sim should work correctly.

 

[priyank1]

Hi audioguru,

I have made the changes which u had recommended, i have breadboarded the circuit exactly according to ur circuit diagram.  My professor at uni has given me a OMNI-DIRECTIONAL ELECTRET MICROPHONE INSERT.. he is suggesting me to insert microphone in the bell of the sthehoscope.

The issue i have is the specification of the microphone insert. On the specfication  it says its operatin frquency is 50-12,500 hz.

My concern is that in order to obeserve korotkoff sounds in branchial artery,frequency of interest is 2- 100 hz. I am not sure if the operating frquency of
50- 12,500 hz will be of any good.

i tried search other microphone inserts but coudnt really find one. Audioguru would u recommend any microphone or microphone insert?

Following is the link to the microphone insert which my professor has given to me.

http://www.maplin.co.uk/SEODynamicPages/module.asp?ModNo=29846

cheers  ;D
pri

 

[audioguru2]

Hi Priyank,
Maplin don't have a detailed spec on that page for the response of the mic. The FAQ has a question, "How flat is the frequency response?" but I couldn't find the answer. Ask them.

Panasonic makes many electret mics which were available somewhere in North America. Their cheap one has a detailed frequency response graph showing that the response is absolutely flat down to 25Hz and probably to much lower frequencies.

View attachment 39748