audioguru2
- Apr 6, 2004
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This original circuit doesn't work here, and doesn't work on the original author's web site. The same complaints about it are there too.
Why not make a simple correction to make it function and make a few more corrections and changes to make it improved?
The professional doctors who use it don't need it sounding like a guitar fuzz distortion circuit!
Why not make a simple correction to make it function and make a few more corrections and changes to make it improved?
The professional doctors who use it don't need it sounding like a guitar fuzz distortion circuit!
I do not care about what is posted on another website.
You seem to think you have some authority here. Build your circuit and it can be posted in the projects section.
BTW: You did not answer my last question. You keep changing the course of your own stream.
MP
You seem to think you have some authority here. Build your circuit and it can be posted in the projects section.
BTW: You did not answer my last question. You keep changing the course of your own stream.
MP
audioguru2
- Apr 6, 2004
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Thanks Doctor Emad,
Your new construction will prove that the corrections work well. The same corrections that were discussed nearly one year ago by other members at the beginning of this thread. They "saw" the errors like I did, but also didn't build it to prove it.
Your new construction will prove that the corrections work well. The same corrections that were discussed nearly one year ago by other members at the beginning of this thread. They "saw" the errors like I did, but also didn't build it to prove it.
Emad, this is not directed at you...
Here is what I posted in April:
http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=620
If you cannot put forth enough effort to build a project, your corrections will fall on deaf ears.
On the other hand, if you build a project and find a correction, then I want to know about it. No one goes around posting a project that does not work for the fun of it. A line or lines in the wrong place or a mis typed value or two usually correct most problems. Replacing the ICs and other parts is not a correction. It is a different design which accomplishes the same thing. It is harder to find the error in a present design than to redraw it. If you take the easy road, don't expect me to recognize it as a correction. Post your "new" design as what it is. A new design.
All members are welcome to post a design to the forum. I expect that it will be something you have built and tested and have a working model.
MP
Here is what I posted in April:
http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=620
If you cannot put forth enough effort to build a project, your corrections will fall on deaf ears.
On the other hand, if you build a project and find a correction, then I want to know about it. No one goes around posting a project that does not work for the fun of it. A line or lines in the wrong place or a mis typed value or two usually correct most problems. Replacing the ICs and other parts is not a correction. It is a different design which accomplishes the same thing. It is harder to find the error in a present design than to redraw it. If you take the easy road, don't expect me to recognize it as a correction. Post your "new" design as what it is. A new design.
All members are welcome to post a design to the forum. I expect that it will be something you have built and tested and have a working model.
MP
MP thank you . Iknow you are right but because I need this circuit Ill try the corrected schematic.I hope it works well.I hpe i have another circuit for the same reason,so if you have another stethoscope circuit diagram plz tell me.Thank you again
prateeksikka
- Jun 19, 2004
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hi audioguru!
there's a bad news.this new circuit gives excellent results on orcad simulation(as desired)but when i made the circuit,it produces a very weak signal at o/p which i thought to be battery noise,what do u have to say?
prateek
there's a bad news.this new circuit gives excellent results on orcad simulation(as desired)but when i made the circuit,it produces a very weak signal at o/p which i thought to be battery noise,what do u have to say?
prateek
audioguru2
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Hi Prateek,
How is the level of the heartbeat signal? It is easy to change.
As I said before, the 741 is a lousy, old and noisy opamp, especially for a low-level microphone preamp.
A modern low-noise opamp, like a TL071 will be much better. Actually, I would use a dual, TL072 for U1 and U2 in one IC.
How is the level of the heartbeat signal? It is easy to change.
As I said before, the 741 is a lousy, old and noisy opamp, especially for a low-level microphone preamp.
A modern low-noise opamp, like a TL071 will be much better. Actually, I would use a dual, TL072 for U1 and U2 in one IC.
audioguru2
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Hi Guys,
As a review, I have posted analysis of faults with this project and my corrections in the Theory Section of this forum, here:
Opamp or Power Amp? http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1630
Low-pass Filter http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1661
Extra Parts http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1663
As a review, I have posted analysis of faults with this project and my corrections in the Theory Section of this forum, here:
Opamp or Power Amp? http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1630
Low-pass Filter http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1661
Extra Parts http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1663
Hi all . I constructed the corrected circuit and I have good amplification when I make clicks with my tongue.,but heart sounds are distorted . there are many cracles and crepitaions with the soundto the extent that no heart sond could be heared when increasing the volume. I used anon shielded wire with the mic and I forgot C7 and C8. Also I put R9 as it is and making short at it does not make a differance. Thats what I did--------------------------------------Thank youuuuuuuuuuuuuuuu
audioguru2
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Hi Doctor Emad,
I am sorry to hear that your corrected circuit doesn't work properly yet.
The first thing that should be done is to use shielded cable to the microphone. It is very important. Non-shielded wire would pickup a lot of mains hum that can overload U1 due to its high gain. Whenever I run out of shielded cable, I just use a piece of shielded RCA-plugs cable, which is the kind that connects the components of my stereo system together (but don't use speaker wire).
The loud crackles that are heard are probably caused by the microphone being in direct contact with your stethoscope head (cone). All applications (hand-held mic, tape recorder and telephone) of microphone elements have them isolated with a rubber mount or grommet. Can you isolate the microphone from the cone but still have it sealed to it, so that movement (friction or handling) of the cone or the patient is not too loud?
C7 and C8 are also important to have, especially with battery powered amplifier circuits like this one.
I am sorry to hear that your corrected circuit doesn't work properly yet.
The first thing that should be done is to use shielded cable to the microphone. It is very important. Non-shielded wire would pickup a lot of mains hum that can overload U1 due to its high gain. Whenever I run out of shielded cable, I just use a piece of shielded RCA-plugs cable, which is the kind that connects the components of my stereo system together (but don't use speaker wire).
The loud crackles that are heard are probably caused by the microphone being in direct contact with your stethoscope head (cone). All applications (hand-held mic, tape recorder and telephone) of microphone elements have them isolated with a rubber mount or grommet. Can you isolate the microphone from the cone but still have it sealed to it, so that movement (friction or handling) of the cone or the patient is not too loud?
C7 and C8 are also important to have, especially with battery powered amplifier circuits like this one.
prateeksikka
- Jun 19, 2004
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hi audioguru;
could you please be specific about these ics i.e tl071 and TL072 as these are not easily awailable in the city where i live(in india) they say that they may have to purchase it from new delhi.any estimate of its cost and availability or for that matter a simpler substitute for it?
thanks
prateek
could you please be specific about these ics i.e tl071 and TL072 as these are not easily awailable in the city where i live(in india) they say that they may have to purchase it from new delhi.any estimate of its cost and availability or for that matter a simpler substitute for it?
thanks
prateek
audioguru2
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Hi Prateek,
The TL071 and TL072 are very common and cheap in North America. They have been used in audio equipment for about 20 years.
A TL071 costs a little more than a 741. A TL072 dual costs less than a 741.
An LM833 dual is also low-noise, and costs a little more than a 741.
Can you get Japanese ICs? A list with a cross-reference has an NJM072, which is the same as a TL072. The list is here:
http://www.microelectr.com.hk/NJRC_datasheet/e05/ae.html
Just ask your supplier what they have for a low-noise single or dual opamp that is used in audio equipment.
The TL071 and TL072 are very common and cheap in North America. They have been used in audio equipment for about 20 years.
A TL071 costs a little more than a 741. A TL072 dual costs less than a 741.
An LM833 dual is also low-noise, and costs a little more than a 741.
Can you get Japanese ICs? A list with a cross-reference has an NJM072, which is the same as a TL072. The list is here:
http://www.microelectr.com.hk/NJRC_datasheet/e05/ae.html
Just ask your supplier what they have for a low-noise single or dual opamp that is used in audio equipment.
audioguru2
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Hi Doctor Emad,
Use a 1K ohms resistor for R16. It prevents a loud "POP" in the earphone if you plug it in with the circuit already powered.
Use a 1K ohms resistor for R16. It prevents a loud "POP" in the earphone if you plug it in with the circuit already powered.
audioguru2
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Hi Guys,
I just finished making a simple test to hear what these noises are all about:
1) 2-wire electret mic from a cell phone. It is mounted in a rubber sleeve.
2) Drilled a hole in a plastic jar lid and pushed the mic into the hole.
3) Biased the mic with a 10K resistor from a 9V battery, like our project.
4) Connected it with shielded cable to an LM386 circuit (my little portable test amp with a low-frequency roll-off of 20Hz).
5) The LM386 circuit has a volume control and a 10uF cap added between pins 1 and 8 for a gain of 200.
6) Stereo headphones from my portable CD player with both 32 ohm channels connected in parallel.
When I talked about 40cm from the mic, it was too loud and I had to turn-down the volume control on the input of the LM386. No distortion then but still pretty loud.
When I held the jar lid with the mic in it against my chest and over my heart, I heard my heartbeat loud and clear! I had to hold the jar lid still to avoid loud friction noises. No hum whatsoever, even with a flourescent light hanging above and electrical stuff all around. The LM386 made a noticeable hiss because it has a gain of 10 times more than what it will have in our project, and is not low-noise with such a high gain. When I talked with the jar lid against my chest my voice was quite loud but muffled, so my isolation wasn't very good. I could also hear my dog barking (she was annoyed by the feedback squeal that I got while moving the mic)and heard the phone ringing in the next room.
If the jar lid is more rigid then it will probably provide better isolation. A "stethoscope head" (cone) should be ideal. The low-pass filter in our project will also attenuate those background noises. I'm glad that our project will have enough gain to do its job.
On my 'scope the LM386's output showed from 1 to 3 cycles of about 25Hz for each heartbeat. Sometimes the single cycle was a rounded pulse of one polarity, and always the same polarity.
So our "corrected" project should work fine.
I just finished making a simple test to hear what these noises are all about:
1) 2-wire electret mic from a cell phone. It is mounted in a rubber sleeve.
2) Drilled a hole in a plastic jar lid and pushed the mic into the hole.
3) Biased the mic with a 10K resistor from a 9V battery, like our project.
4) Connected it with shielded cable to an LM386 circuit (my little portable test amp with a low-frequency roll-off of 20Hz).
5) The LM386 circuit has a volume control and a 10uF cap added between pins 1 and 8 for a gain of 200.
6) Stereo headphones from my portable CD player with both 32 ohm channels connected in parallel.
When I talked about 40cm from the mic, it was too loud and I had to turn-down the volume control on the input of the LM386. No distortion then but still pretty loud.
When I held the jar lid with the mic in it against my chest and over my heart, I heard my heartbeat loud and clear! I had to hold the jar lid still to avoid loud friction noises. No hum whatsoever, even with a flourescent light hanging above and electrical stuff all around. The LM386 made a noticeable hiss because it has a gain of 10 times more than what it will have in our project, and is not low-noise with such a high gain. When I talked with the jar lid against my chest my voice was quite loud but muffled, so my isolation wasn't very good. I could also hear my dog barking (she was annoyed by the feedback squeal that I got while moving the mic)and heard the phone ringing in the next room.
If the jar lid is more rigid then it will probably provide better isolation. A "stethoscope head" (cone) should be ideal. The low-pass filter in our project will also attenuate those background noises. I'm glad that our project will have enough gain to do its job.
On my 'scope the LM386's output showed from 1 to 3 cycles of about 25Hz for each heartbeat. Sometimes the single cycle was a rounded pulse of one polarity, and always the same polarity.
So our "corrected" project should work fine.
audioguru2
- Apr 6, 2004
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Hi Doctor Emad,
U5 is the LM386 audio power amp IC. It drives your earphones.
U1 and U2 should be low-noise opamps such as the TL071.
U4 can be just about any opamp.
C3 and R7 connect together and to pin 6 of U2, the volume control and to pin 3 of U4.
Please see my corrected schematic of this project on page 7 of this web-thread.
I'm glad to help you with this project.
U5 is the LM386 audio power amp IC. It drives your earphones.
U1 and U2 should be low-noise opamps such as the TL071.
U4 can be just about any opamp.
C3 and R7 connect together and to pin 6 of U2, the volume control and to pin 3 of U4.
Please see my corrected schematic of this project on page 7 of this web-thread.
I'm glad to help you with this project.
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