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Emad

Electronic Stethoscope 2

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Hi Doctor Emad,
20nF won't make much difference and 100nF will cause the filter to filter-out most frequencies. 4.7nF will make a big difference.

I am glad that you find my corrections to this project to be working well. You can post the circuit anywhere you want.

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hi audioguru!
sorry for the delay in reply i was busy in making this circuit for few days. i have made it using the ics which you recommended. much better response.working well as EMAD said but by using a high power headphone as in a walkman radio.
(i myself used it)
any comments on that. anyway thanks for the corrected circuit.awaiting early reply.
prateek

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Hi Prateek,
I am glad to hear that your project is also working well.
I am sorry that you wasted "3 precious months of my college life working on this project", until I fixed it.
Before you also said that the ICs that I recommend were difficult to obtain. How did you get them?

The LM386 that the corrected project uses is designed to drive a low-impedance load, like your high-power headphones. I recommend your type of headphones. Small ones do not reproduce the very low frequency heartbeat sound very well.

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hi audioguru!
Sorry for wasting your precious time working on this project. I got these ICs from new delhi,india through one of my friends.thanks once again for your cooperation.Now when it is finally over,i wish to ask about you.are u a student?what do you do? where do you live,if you are getting some time out of your professional life,do send me some reply on these questions.
do send me a private message along with your e-mail i.d(if you dont object) thanking you once again and awaiting early reply,
prateek

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Hi Audioguru.
I built this circuit with the TLO72.
There is mutch noise. When lowering the volume there is a sound like hissssssss ,then after slight raising of volume heart sound is very laod and there is nearly no effect of increasing the volume .
My mic cable is about 2 meter long but it is well sheilded. I use a real stethoscope head that already amplifies the sound before coming to the mic.
What about putting R3 again in the circuit???? and what is your advice???

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Hi Doctor Emad,
I am sorry, but it sounds like your volume control is broken or that U5 has way too much gain.
The LM386 for U5 shouldn't have anything connected to its "gain" pins 1 and 8 . Then it will have a gain of 20 and very little hiss. See if pin 1 or 8 isn't accidently grounded which would increase its gain enormously.

R3 didn't do anything in this circuit. It would be used with a high input bias current opamp like a 741 where you want the opamp's output to be exactly 0V DC. Then the value of R3 must equal R4 (it was 20 times less). The input bias currents and the resulting voltage drops across R3 and R4 at the opamp's inputs would cancel. The TL072 has FET inputs which have an extremely low input bias current. R4 would need to be many tens of megohms for adding an equal-value R3 to have any effect.
Some people say that the "resistor noise" of R2 is cancelled by similar noise from R3. But random events at both opamp inputs don't cancel.
Try R3 and fix your volume control or U5's wiring.

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Hi Audioguru
Ihad reversed the variable R and had controle on volume .
The sound is good in about 1/4 the range of the volume controle or less ,then there is mutch distortion.
By putting 1k risistor paralell to R4 the noise disappear but heart sound become weak and respiratory sounds are not percepted.
I think this circuit needs some slight modifications that I dont know.
thanks for help.

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Hi Doctor Emad,
I can see (hear?) how reversing the terminals on the variable volume control makes the sound jumpy. I never thought of that and I am glad you discovered it.
You are on the right track by reducing the gain by reducing the value of R4. But you reduced the gain too much, about 48 times!
Also, the TL072 cannot drive a resistor as low as 1K very well.

Try connecting 22K across R4 to reduce the gain about 3.1 times which is 10dB.
5.6K across R4 will reduce the gain about 9.4 times which is 20dB.
I think you will find a suitable value for R4.

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AudioGuru,

In your recent reply in Aaron's Forum you discussed adding another diode and a 100K resistor. Would it be possible for you to make a quick sketch of the circuit. Is this the same 100K resistor you suggested to get the bias setup for pin2 of the 555?

Would it be better to add a full wave bridge to the output of the electronic stethoscope and then lead the positive output of the bride to pin 2 and the negative going to ground of the stethoscope?

Quote:

BTW, your rectifier will need a second diode, with its cathode connected to the 555's positive supply, and its anode connected to the junction of the cathode of the other rectifier and the Stethoscope's output cap. Connect a 100K resistor in parallel with this new diode. Then the polarity of the Stethoscope's output cap must be reversed.

Thanks,

Del

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Hi again Del,
Welcome to our community on this website.
Now that you have successfully constructed our Electronic Stethoscope-2 project and wish to use it to activate a burglar alarm, I can't remember why you wanted to use a 555 timer IC.

I have sketched a simple transistor circuit to be connected to the stethoscope's output that will activate a silent alarm for a few seconds each time a noise is picked-up. It uses a half-wave rectifier. A full-wave rectifier would require many additional components (or just a center-tapped audio transformer plus another diode).

post-1706-14279141951998_thumb.jpg

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Audio,

Thanks for the quick reply. This may sound dumb but what does TR1 stand for? It looks to me to be a transistor. If it is what type and value would be correct.

The use of the 555 was was give a time delay before all the sirens go off. nothing better than to let the intruder think he got in undetected and then when he least expects it everthings goes off, sirens, warning that the police will be there in less then 30 seconds, fake gas release to make him think tear gas has been released and an anounced warning that if he doesn't get out immediately all doors and windows will become electrified with high voltage. This should scare the pants off of any intruder. He should drop everthing and hightail it out of there pronto.

But don't worry I won't be using real teargas or electifing the door and windows. I'll just play a tape of nasty electrical discharge and have a CO2 canister release, which will look like gas is being released. I bet he never comes back to my house again. Better to pick a house where he'll feel safe. The mind can be a powerful weapon of defence when it is played out correctly.

Del

Try out a tube of that special solder. I think you'll find it as good if not better than the stuff you are using. Thanks again for all of your help. If you ever need a chemistry type question answered please feel free to contact me.

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Hi Del,
You are correct, TR1 in my add-on circuit is a transistor, the type depending on the load.

It would be hillarious to watch a video of an intruder who is startled by your sound effects and fake tear gas! He would jump right out of his skin.

A problem with using a 555 as a delayed activation timer is that its output is the same before being triggered as it is after the time period. It is designed to give a timed output duration beginning immediately after being triggered. I don't even think it will work with 2 cascaded 555's, with the 2nd being triggered when the 1st times-out. The 2nd would be triggered continuously prior to the 1st being triggered.
Another problem is that the trigger input signal must be released just prior to its timeout, which probably won't happen with a noisy burglar. It wouldn't be difficult to gate the trigger off during the time period.

I fixed a project here that changes the brightness of a blinking LED depending on the resistance of an object between its probes. It uses an AC signal between its probes to avoid ion migration and probe plating/unplating and has a range of a few thousand. Although originally intended to indicate the dryness of a plant's soil, another chemist used it to indicate salts concentration in a solution. Maybe you can use it like that or to indicate that a chemical reaction has finally occurred. The project is here:
http://www.electronics-lab.com/projects/science/018/index.html

I will try your recommended "silver solder" and get the lead out.

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Hi Doctor Emad,
I have added C7, C8 and R16 to this project so it should operate well with two inexpensive 9VDC/300mA or more "wall wart" power supplies. If mains hum is heard with the volume control at zero, a 47uF capcitor can be added from the LM386's pin 7 to ground which will reduce its hum to less than 1/140th. Keep the power supplies' wires away from the project's input stages and volume control.

Did you solve the problem that you had with too much input gain?

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I got the first stethoscope design to work. It works well. However, I tried building stethoscope #2 from scratch exactly as described and I get no sound at all. I had to build this circuit for a lab project. Due to time constraints, I'll be presenting the first design. Design #2 sounds awesome but can't get it to work.

Thanks for all of your discussions. They helped me go in the right direction.

mannyt01

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audio guru its ok i see someone couldent get the stephoscope 2 working so changes were done or needed to get it going , i need to get the full details here and read the seccessfull tests by those who have biult it and tried it ,

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thanks audio guru i wait patiently to read your postings its better than the news papers, electronics lab is lucky to have you as a member and electronics god , your our exspert on this matter of audio electronics and other things hence the name audio guru

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:)audio guru ive got a printout of your electronic stephescope 2 circuit, thats the one that works insent it, anyhow which part of r11 do i run to pin one of the tlo72 ic to make it into a good parabolic microphone circuit , is it the ground wire or the wire before that ,that goes to the optional circuit.ive used circuit maker to redraw your circuit into a better to biuld by formatt , for me and ive left out the optional circuit that im not useing

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audio gurus electronic stephescope 2, audio guru ive redrawn it so its simpler to biuld be all gronds are grounded and ive linked one of the postive inputs from the first ic, to the second post input ive put letters ab and c near r11 so which ones or is it the ground or the wire before that, that goes to pin 1 od the tlo72 ic to make this circuit into a good parabolic mic circuit

post-876-1427914199738_thumb.jpg

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