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Electronic Stethoscope 2


Emad
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Hi, audioguru :D

I don't know about being back, it's more of the case that I've found some time away from taking care of my son Ethan, and my partner and daughter aren't hogging our shared dial-up Internet connection playing neopets ;D.

I think it was about 12 months ago when I made it, it didn't work as well as I had hoped, that is for what I wanted to use it for, but it does work very well for what it was intended to be used for ;), and with the modifications that you help me with audioguru, it works very well for tuneing into respiratory sounds or heartbeat sounds 8).

The green caps that you can see are not correct, I was just experimenting with different capacitors ;D.

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Hi audioguru :)

That microphone case is one of many that I made and tested ;), it's a lid from a deodorant aerosol tin, I used cloth stretched over the bottom that's held in place with a cabletie, I then used a type of rubberised foam to insulate the rest of it, which is held in place with electrical tape.

The cloth almost eliminates friction noises, but in using the cloth the seal is no longer very good, and allows for some outside noises to be heard, but the rubberised foam that encase the rest of it, helps reduce outside noises.  So there is a bit of a trade-off.

I also tried using headphones that completely covered my ears, and Yes it did make a difference.

Dazza :).

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  • 4 months later...

heyz.. audioguru....

had been working on ur circuit.... i did use a function generator to input some signals.. the output was quite ok.. not much noises.. i cant hear anything using the mic though.. maybe i burned it while soldering... hehe..

anywaes.. do u have the circuit diagram in .ckt format? i need to change it to pcb.. or better maybe straight the pcb diagram..?? =)

dazza... ur box looks cool.. good job..

thanx..

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if i wanna connect a speaker to the circuit.. how do i do it?

Plug an 8 ohm speaker into the jack for the headphones. The LM386 power amplifier IC will provide the speaker with 450mW max and probably cause acoustical feedback howling because the microphone will probably hear the speaker.

will the led cont to light up when i turn the swith to off?

For a few seconds while C7 and C8 slowly discharge.

its contant blinking when i switch it off.. till i unplugged the batt
connection

Then your switch is not wired correctly. Look at my schematic with the switch turning both batteries on and off.

post-1706-14279143085482_thumb.png

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mr audioguru...

Bell (20-200 Hz) - Diaphragm (100-500 Hz) - Extended Range (20-1000 Hz)
these are the ranges that a normal stethoscope can or should detect... can this circuit be likewise? wat changes needed to be done to the circuit to achieve this modes...?? wat is the frequency range of this current circuitry... hope u can reply me asap.. thanks....

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the speaker has +ve n -ve.... how do i connect it? the positive to pin 5 of lm386? the negative to ground?

You never connect a speaker directly to pin 5 of the LM386 because it has a DC voltage. A speaker or headphones must connect to the output of C6 which is the output DC blocking capacitor. The jack for the headphones is where to connect a speaker.

im still having trouble connecting the power supply.

Two batteries and a switch that has 2 poles. I showed you how to connect them.

Bell (20-200 Hz) - Diaphragm (100-500 Hz) - Extended Range (20-1000 Hz)
these are the ranges that a normal stethoscope can or should detect... can this circuit be likewise? wat changes needed to be done to the circuit to achieve this modes...?? wat is the frequency range of this current circuitry?

C2 passes frequencies down to about 2.8Hz. C6 passes frequencies down to 10Hz into stereo 32 ohms headphones (16 ohms total). Therefore the overall low frequency cutoff frequency (-3dB) is about 12.5Hz.
The Sallen and Key Butterworth lowpass filter of U1b provides a highpass cutoff frequency (-3dB) of 103Hz.
The highpass filter will have a cutoff frequency of 212Hz if R5 and R6 are changed to 16k.
The highpass filter will have a cutoff frequency of 1.03kHz if R5 and R6 remain as original and when C3 and C4 are changed to 4.7nF.
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now it works... meaning there is sound output.... but theres a constant *tick-tock* sound when the power is turned on. meaning.. my led will blink twice evry other second even without me talking into the mic

Maybe your batteries are old with a high internal resistance which causes the supply voltages to jump around. Try new 9V alkaline batteries.
Does the blinking stop when the volume control is turned down?

when i touch the mic... it will have sound output... but rather noisy..

You are not supposed to touch the mic because it responds to very low frequencies and it is extremely sensitive.

Did you try connecting a speaker to the headphones jack? Did the project then make acoustical feedback howling?
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dear audioguru...

i dun think its the batt.... it still has 7V+.. =)
volume min = LED flashes fast
volume max = LED blinks steadily.... blue then red... blue then red.... (tick-tocks)

i attached a speaker... theres sound... no howling..... (ticks tocks)
i attached headphones... very loud *tick-tocks* according to the situation above..

*puzzled*

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7V for a 9V battery and with the low current of this project is a battery that is wearing out. When it reaches 6V then it is dead.

Did you connect everything together with the "ground" symbol on the schematic?
Did you connect everything together with the "+9V" symbol on the schematic?
Did you connect everything together with the "-9V" symbol on the schematic?
Did you substitute any parts?

Please measure and report here the DC voltage measurements to ground of the microphone, pin 1 of U1, pin 7 of U1, pin 6 of U4 and pin 5 of U5.
Please look at the connections and parts values on the schematic again.

post-1706-14279143087732_thumb.png

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  • 2 months later...
  • 2 weeks later...

The electret microphone is polarized so its terminal that is connected to its metal case is ground.
The project needs a two-wires electret microphone from a toy or from a telephone. A three-wires electret microphone needs a different circuit.

Maybe you have a condenser microphone. It is different than an electret microphone because it needs a 48V external power supply to bias it.

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I am sure that my microphone is biass in this circuit,beaucuse befure this circuit,I test Electronic stethoscope circuit , I could hear my sounds in 8 ohms speaker,but there were so much noise that I couldn t hear heartsounds .
after that I test electronic stethoscope 2 , I couldn t  hear my sounds(I mean my speaking sounds) and I couldn t hear heartsounds too but I put the stethoscopehead  on my neck and I could hear some frequencies and when I rub stethoscope I coud hear it sounds,so I thing my problem is mic,(it has 2 wire) :'( ??? :(
maybe there is problem beetwin mic and stethoscope head,Should I past and press them togather ?

This is very urgently,I should finish it next week.
thanks.

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I took a thick plastic lid from a jar and drilled a hole in its center for my electret microphone. Holding it up I could hear the low frequencies clearly in my earphones when somebody spoke fairly far away. When I pressed the jar lid to my chest so that the microphone has a small air space from it to my skin then the surround part of the lid blocked background noises but the microphone picked up my heartbeat loud and clear. The volume control adjusted the sound to be nothing or to be loud.

You must use earphones not a speaker to avoid the microphone hearing the speaker and causing acoustical feedback howling noise.
You must use shielded audio cable to connect to the microphone to avoid mains hum pickup.
Did you substitute any parts?

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