Electronic Stethoscope

[TriGeminal]

After a while I decided reloaded the project again, I still use the breadboard but just re-connected the wires and get longer wires with clips for the batteries and speakers ..

I connect it to the audio card in my computer and I get this noise all the time (even if I removed the entire mic!)

Is it receiving signals from air or something?

Thank you

problem.zip

 

[audioguru2]

Hi TriGerminal,
The circuit has high gain and could pickup interference from the air if it is not built compact on a pcb or on Veroboard or does not use a shielded audio imput cable.

Your circuit produces a static noises and a low frequency oscillation called "motorboating".
Does the LED oscillate slowly like the sound?

Did you substitute any parts?
Are the 9V batteries fairly new? What voltage are they while the circuit is powered?

 

[TriGeminal]

Does the LED oscillate slowly like the sound?

It's doesn't give any light (maybe hardly I can see it!)

Did you substitute any parts?

yes, R12 instead of 330k I put 270k because I lost my 330k .. also I connect solid single wires with standard several fine wires ones

Are the 9V batteries fairly new? What voltage are they while the circuit is powered?

They're the same I used the first time, but I didn't measure the voltage

 

[audioguru2]

Hi TriGerminal,
Your circuit motorboats and the LED doesn't light. So I think one or both of your batteries are dead.
The circuit makes a little amount of noise that is amplified. When the opamp tries to drive current into the LED then the battery voltage collapses and the noise stops, then the battery voltage slowly builds up again and the problem repeats over and over.

Measure the battery voltage on the circuit while the circuit is making the slow oscillation. Maybe the clips from the batteries are making a poor connection.

 

[TriGeminal]

Sorry, belated

I measured the batteries .. one was 8.4v and the other was 7.2v! I think that difference might be counted

 

[audioguru2]

I think the project should work fine when the batteries measure a minimum of 6V while they are powering it.

What load resistance do you have at the headphones jack? If it is 8 ohms or less then the positive battery has a high current drain when the sound is loud, possibly dropping its voltage too low. That would cause the circuit to motorboat.

Try new alkaline batteries.

 

[Emad1]

Hi all
Ihave made the original ,the corrected and the elect. steth. 2 about one year ago
The original didn t work and the other two worked.

The  best one was the corrected circuit.

The stethoscope should hear the sounds between the 1st and 2nd , and the 2nd and 1st heart sonds , like murmours as systolic and diastolic , also clicks and so on.
So there shoud be no noise .
I hope to find a new project using 3v supply and a small head phone like that used with mobile . This will be more practical and I can use it in my clinic.
Thanks to all especially audioguru.

 

[priyank1]

Hi all, Hi audioguru...

I have tried the modified circuit, but sadly it didnt work for me. I need to clarify one thing in the circuit. IS pin 4 of u5 (lm386) ground or connected to the -9 volt  supply. Some of the post in forum have suggested to connnect pin 4 to the -9 volts. why would that be? I went through the datsheet of lm 386 which suugests to ground pin 4. i have built the plastic diaphragm for the microphone insert and have breadboarded the circuit according to the circuit diagram. WIth me i dont get any out put when i connect output from pin 5 of u5 to my a/d converter of the dspace card . i have also used shielded cable for the microphone part.

ANy suggestion please....have attached pics of breadboard and the plastic diaphragm for the microphone insert

cheers
pri

[attachment deleted by admin]

 

[audioguru2]

I have tried the modified circuit, but sadly it didnt work for me. I need to clarify one thing in the circuit. IS pin 4 of u5 (lm386) ground or connected to the -9 volt  supply.

Pin 4 (and pin 2) of the LM386 should be connected to ground (0V).

Some of the post in forum have suggested to connnect pin 4 to the -9 volts. why would that be?

Because the original project has an error in its parts list and says to use a 741 opamp for U5. A 741 won't work with its pin 2 connected to its pin 4 but works a little with -9V on its pin 4.

i dont get any output when i connect output from pin 5 of u5 to my a/d converter of the dspace card . i have also used shielded cable for the microphone part.

Pin 5 of the LM386 has a DC voltage that idles at half the positive supply voltage. Then its output voltage swings down to about +1V and up to about +8V. The +8V is too high and might damage your a/d converter. You need to convert the signal to a voltage range of from 0V to +5V for the a/d converter.

If you cannect a speaker or headphones to C6 do you hear anything?
Do the LEDs flicker when there is sound at the microphone?View attachment 39969

 

[intel1]

My name is mahesh .Some one could u tell me how to give the INPUT. Reply as soon as possible

 

[audioguru2]

Hi Mahesh,
The input to the electronic stethoscope project is the low frequency audio sound of heartbeats. The electret microphone picks the sound up and the circuit filters out background sounds and amplifies the heartbeat sound.

 

[subodhthok]

Hi All....
This circuit works perfectly using LM386 at U5. Now will it possible to put a display (LCD/LED) at the output where it can count the heartbeat?

 

[audioguru2]

Hi Subodhthok,
Welcome to our forum. ;D
It is good that it works perfectly.

The circuit has AC signals. Digital counters use DC pulses, not AC as their input. In order to count heartbeats then the signal must be rectified into DC pulses but the polarity of the pulses might be negative instead of positive. If the pulses are negative then they need to be inverted to be used as a clock input to a Cmos counter IC.

 

[subodhthok]

So please send me a cct diagram to fit Display. I'll be indebted.
Can the cck be like....

O/P from cct->Sample cct->Counter->Display

Help me with a cct diagram that's most likely to work. I'll try it!

Thnx in advance

 

[subodhthok]

And I'm needing a bit urgently............ ;D

 

[MP1]

subodhthok,
I think you are looking for this project:
http://www.web-ee.com/Schematics/HeMon/HeMon.htm

MP

 

[audioguru2]

Hi Subodhthok,
You must design the interface circuit yourself or ask your teacher to help you.

The output pulses of U5 are only plus and minus about 3V if the batteries are new, and only 2V if the batteries are old. A rectifier would reduce it to be too low to drive logic circuits.

The output pulses of U4 are plus and minus about 7.5V when the batteries are new. A rectifier would reduce it to 6.8V. A voltage divider made with two resistors would reduce it to 5V for logic circuits.

My stethoscope made heatbeats that were sometimes made of 16Hz vibrations for each beat. A filter would need to be made to integrate the rectified pulses into single beats.
The rectifier should drive an Schmitt-trigger inverter or Schmitt-trigger buffer that can be used if pulses of the opposite polarity are best.

 

[Steve_hi]

Hi Guys Just to let you know I just completed Stethoscope 2 and it works well I do have however a constant hum coming from my hesdphone does anyone know if it would be resolved with a better headphone or would it not accomplish anything. thank you for your reply

 

[audioguru2]

Hi Steve,
It is good to hear that it works well. ;D

Hum is mains radiation picked up by the high gain input. Unshielded input cable usually causes it. If the wiring of your circuit is long like on a breadboard then it picks up mains hum.

Use shielded audio cable from the microphone and keep all unshielded wires very short.
I show the shield on the microphone cable on my schematic.

 

[cshaopin]

I'm a newbie here. How can i send the output of the electronic stethoscope to computer through serial port ? I use MATLAB to receive the signal.

I need a ADC and a Microcontroller as well as the RS-323 to do that ?

The level of the signals must be shifted to the positive range before i can digitize it rite ?