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Everything posted by CDAK

  1. Dear friends, Sorry for not being present for the discussion. Just like MP said, I've ,made a successful project (a gadget) out of the circuit given in this discussion. It successfully detects 25 different heart diseases and now I'm on my try to commercially implement this. But the problem comes only on the Head design( not in the circuit). But I got some creative suggestions form this forum later and till now I couldn't try it out. I'll sure inform all the outcomes. Regards CDAK
  2. MP, I haven't yet started further work in the project. It may take a few weeks to restart. (I finished my course in the current institution and may go back start working in another environment. So it may take few weeks to come back to the project again.) I shall inform every step in the enhancement work. The first thing I would try will be ur expander circuit. Then a notch filter ( audioguru also suggested it, thanks). I had this notch filter idea, but since I had a long signal processing left in that work, I left the hardware there. Reagarding the HPF, I haven't used any amplification and even without that it worked well in MATLAB ( .wav format keeps the value between +1 and -1). Audioguru, I don't know why it is obsolet if somebody uses an available chip ( atleast it was available to me)... CDAK
  3. MP, till now, I was extremely busy with my thesis work and was in a struggle to get proper result. Finally,my work ended with a success note. The credit goes to this forum too. I'll try ur expander circuit idea as I'm going to do more specialised work on the design of the stethscope part, in order to improve my diagnosing system. I'll inform the timely improvement of the system. CDAK
  4. The second figure (normal heart beat from a standard e-steth)
  5. Sorry once again for the late reply. Thanks a lot MP and audioguru for the healthy discussion between u. Here I give my reply to some of the questions asked by u during ur discussion. The e-steth I made works fine with the circuit modified by me. I don't know whether LM387 is commercially available or not, but it was available in bulk in my Institute lab. So I made use of it and got the desired output. As I told earler, for the analysis work ( my work is not just an e-scope but the analysis is also there), I took the pre-amp out. I used sheilded cable from mic to amp input. I haven't done the body-grounding, but the low frequency interference is reduced with a 7th order digital highpass filter (cut-off at 60Hz) after recording the sound from the e-steth in .wav format. I've given a set of figures showing the sounds recorded and then the HPFed version.The first set shows a normal heart beat on the left hand side and its HPFed version on the right hand side. It's clear that the filtered version is almost same as that from a standard e-steth(second fig). The second figure is given only for the comparison purpose and here RHS figure is a single beat of the one on the LHS.
  6. It's very difficult to get the fidility that a professional hi-fi e-scope gives, by the design over here. The main problem is the head design . We need specially designed head that absorbs sound of friction and other distant voices and sounds. Human body absorbs almost all sound (like Fan's, A/C's , CPU fan's,....?)which is then heard through our e-scope.So it is virtually impossible to get a clean heart sound through the scope. For the analysis, I took the signal out from the pre-amp out (otherwise signal will be clipped while recording)and then it is digitally filtered.(9th order Chebyshev LPF). The sound recorded at 8 KS/Sec at 16 bit resolution. Later, I'll post the picture of my e-scope system( now it is fully in a case)
  7. Sorry for the delay, I couldn't come to the forum for a few weeks. I used my circuit to record a few heart sound. Here I give a plot of a heart beat (fig.1) recorded by my e-scope and fig.2 is the one downloaded from a medical site. The noise in my plot is from the surroundings(low frequency interferences) and is not electronic noise.(I've used a digital LPF too). The explanation and the problems in the circuit will be posted very soon. CDAK
  8. Thank u Bogdan, Infact, I had reduced the pre-amp gain.But later, found that for different people(patients), we need to vary the gain.So I introduced 2 more controls in the circuit.(in the pre-amp ckt only). One is in the microphone bias and the second is in the gain control. The circuit is attached.(only that part is shown from the total circuit.) CDAK
  9. Here I suggest a modification to the e-scope circuit. Instead of using 741 everywhere, use the low noise pre-amplifier LM387 at a high gain at the input stage. In the attachment, it is given. U1 is LM 387 designed for a gain of above 500. It functions only above 10v eventhough it's minimum supply voltage is +9v. So I took 12v and is used in all other ICs too. 387 uses +ve and ground( no negative). So for couplilng to the next stage , a coupling capacitor is to be used(0.1 uF is used here with 100k to the ground) In the figure,at the input, cap stands for condenser mic. The second stage,(butterworth second order LPF), designed at 600 Hz cutoff. I got satisfactory result, except for my microphone picks up even the distant talk and the heart beat is heard in between all other sounds( not exactly the noise in electronics)!!! Any remedy for that ???
  10. How good is this e-stethscope ckt in obtaining the real heart sound? Anybody tried? My work is related to that.( I can't go for an e-steth available in market as it is too expensive for me. ) I haven't yet started my work.I 'll inform u the outcome of each stage..thank u. :)
  11. I got a doubt in the ckt.One of said, the last section is an amplifier, but without feedback will it work as a practical amp? Why do the usage of LM386 restrict to the last one only?(or what's wrong if one replace all 741 by 386 for better snr?)
  12. Hi friends, :) I'm a new member from India. I found this site is very useful for the hardware people. As a part of my project (I'm doing my masters in Engg.), I've to make use of an e- stethoscope. So,I'm going to try out the circuit given here. But it will take some time to get some result as I can start my hardware work from next week onwards only. I expect ur help and sggestions. Thank u all
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