Electronic Stethoscope 2

[hakyman]

Hi Audioguru Happy new year too. i also checked the circuit(elec. steth.-2 project) and it really works good but i have problems with earphone i use a sony ear-in headphone and one of its ear burst. i still got some pit pats(pıt(seemed like this because my alphabet is not suit i checked the datasheet of TL072 and they named the o/p of first opamp in TL072(pin 1) as offset-null pin. i cant understand what it is(datasheet from ST microelectronics the producer site)i send the pin connection jpg. and i'd like to ask what is the purpose of peak detector using on converting the o/p of electronic stethescope to digital?
Thank You so muuuuuuuuuuuuuuuuuuch audioguru u helped me to get over this if you send me a good earphone it ll be perfect ;D thank u so much again ...

View attachment 36408

 

[audioguru2]

Hi Hakyman,
I am glad to hear that your Electronic Stethoscope-2 project really works good.
1) It is too bad that your broken Sony earphone makes a "pit-pat" sound that your language alphabet or fonts can't reproduce.
2) Pin #1 on a TL072 is "the output of its opamp #1".
3) I recommended rectifying the 30Hz output, peak detecting and filtering it so that each heartbeat will look like a DC pulse on a computer monitor's screen. I don't know why AC 30Hz is produced by the circuit when the heart makes a single DC pulse for each heartbeat. Maybe the skin is vibrating or the air under the stethoscope head is resonating.

I am sorry that I can't send you a good earphone. Just beg, borrow or steal one! ;D

 

[hakyman]

hi Audioguru
i see u r online and i'd like to ask that what kind of earphone u recommend?
thank for helps i dont know how thanks to you
i'm trying a new stethescope project with lf353 i ll send the circuit when i finished modyfying thank again ...

 

[hakyman]

Hi Again.
I've got some questions about audio application and the electronic stethescope-2 project components. i need the reasons of selection of the components.
1)why u choose theC7=1000uF and C8=470uF and what is the purpose of these components?
2)there are so many electret mic powering circuits in different values of components why you choose C1=470uF R1=10K and R16=1K what is the purpose?
3)U1a is a buffer and why we choose the gain about Kv=22 what if when we adjust the gain in lower or higher value?and why all buffer and booster circuits have negative feedback? why non-inversing input not select?To avoid the offset or the noise?
4)U1b is a low pass filter with the cutoff frequency 103Hz but why you choose this frequency why not 200Hz -- the max frequency of heart sounds?and if we choose the values like; C3=C4=100nF and R5=R6=1.5K(it gives the nearest cutoff value about 106Hz)i mean why you choose these values any reason for that?if i change them with the values i gave above, will be any differences?
5)what is the purpose of R7 and R8 why you need the feedback and how you define the values of R7 and R8?
6)why you dont use the bypass pin of lm386(pin 7)? what means bypass?
7)what is the reason to choose the rectifier circuit(C6 and R15) values why 1000uF why not another value why 15K.
8)what is the purpose of using C5=0.1uF and R14=3.9 as little value as this?what if we remove it or change?
9)has the filter part any effects on gain?
10)anybody calculate the matematical models of the circuit?
11)don't we need a High-Pass Filter.isn't be better with this ?
12)what if we change the LM386 with a different amplifier as 20W or 30W ?is the pre-amp part o/p can drive the power amplifier has a power of 20w or more ?
Additional Basic Questions;
1) what is a pre-amp and what is main reasons for using. which part it has got to have? buffer,filter,booster,...?
2)what is a booster what is its purpose?
3)what is buffer what its purpose ?
...
it goes like this ;D i want to know them totally i know some but i havent got a real background on audio electronics so i cant set up the relations efecting each other. Thanks to all who try to help me and answer my Questions thanks....
here is the schematic again if there is anyone not see before still

View attachment 36415

 

[hakyman]

Hi Again.
I've got some questions about audio application and the electronic stethescope-2 project components. i need the reasons of selection of the components.
1)why u choose theC7=1000uF and C8=470uF and what is the purpose of these components?
2)there are so many electret mic powering circuits in different values of components why you choose C1=470uF R1=10K and R16=1K what is the purpose?
3)U1a is a buffer and why we choose the gain about Kv=22 what if when we adjust the gain in lower or higher value?and why all buffer and booster circuits have negative feedback? why non-inversing input not select?To avoid the offset or the noise?
4)U1b is a low pass filter with the cutoff frequency 103Hz but why you choose this frequency why not 200Hz -- the max frequency of heart sounds?and if we choose the values like; C3=C4=100nF and R5=R6=1.5K(it gives the nearest cutoff value about 106Hz)i mean why you choose these values any reason for that?if i change them with the values i gave above, will be any differences?
5)what is the purpose of R7 and R8 why you need the feedback and how you define the values of R7 and R8?
6)why you dont use the bypass pin of lm386(pin 7)? what means bypass?
7)what is the reason to choose the rectifier circuit(C6 and R15) values why 1000uF why not another value why 15K.
what is the purpose of using C5=0.1uF and R14=3.9 as little value as this?what if we remove it or change?
9)has the filter part any effects on gain?
10)anybody calculate the matematical models of the circuit?
11)don't we need a High-Pass Filter.isn't be better with this ?
12)what if we change the LM386 with a different amplifier as 20W or 30W ?is the pre-amp part o/p can drive the power amplifier has a power of 20w or more ?
Additional Basic Questions;
1) what is a pre-amp and what is main reasons for using. which part it has got to have? buffer,filter,booster,...?
2)what is a booster what is its purpose?
3)what is buffer what its purpose ?
...
it goes like this i want to know them totally i know some but i havent got a real background on audio electronics so i cant set up the relations efecting each other. Thanks to all who try to help me and answer my Questions thanks....
here is the schematic again if there is anyone not see before still

View attachment 36416

 

[audioguru2]

Hi Hakyman,
You have many questions, let's see if I can answer them.
1) C7 supplies positive supply current when the positive battery runs down and its internal resistance rises. The LM386 power amp draws a fairly high current during heartbeats and you don't want the supply voltage to fluctuate.
C8 does the same for the negative supply, except its current is less.
2) R1 is the drain load for the Field Effect Transistor inside the electret mic. R16 and C1 is a supply filter circuit to keep supply voltage fluctuations away from the circuit's sensitive input. Without this filter, the circuit might "motorboat" when the battery runs down.
3) U1a is a preamp with gain. A buffer usually doesn't have gain. The gain is not 22, but is actually only about 3.9 since the drain of the FET inside the electret mic is a high-impedance current source, therefore the opamp's input resistor is R1 plus R2. The preamp's gain of 3.9 plus the LPF's gain of 1.6 matches the output level of the electret mic to the fixed gain of 20 for the LM386. You can change the gain of the preamp by changing the value of R4.
Negative feedback in an opamp circuit reduces its output impedance and distortion, and makes the gain predictable. I think that the higher input impedance of a non-inverting preamp would work better in this project.
The low-noise opamp and fairly low-value resistors reduce noise in the preamp circuit.
The input coupling cap prevents the preamp from amplifying its small offset voltage.
4) The LPF works well with a cutoff frequency of 103Hz. You can change the frequency by changing the equal values of R5 ands R6, or C3 and C4. R5 and R6 should not be less than the 2K value that is the minimum load resistance for the preamp.
5) R7 and R8 can have any total resistance from 2K to about 1M. Their ratio must remain as shown to make the gain 1.6, which is what is required for an "equal-value resistors and capacitors, Sallen and Key LPF". The negative feedback in the LPF sharpens the cutoff so that it has a flat Butterworth response.
6) A cap at the bypass pin of the LM386 would reduce mains hum if a cheap power supply with ripple was used. It filters the input bias voltage of the LM386. Bypass means filter.
7) C6 and R15 are not a rectifier circuit. C6 couples the audio but blocks the half-supply DC voltage at the output of the LM386 from going to the earphones. R15 stops the earphones from making a very loud "pop" if they are plugged-in with the power already turned on (the earphones would quickly charge C6). The 1K value for R15 fully-charges C6 in 1 second.
The value For C6 is chosen to be a low reactance at 20Hz. Two paralleled 16 ohm earphones will cause a 3dB loss at 20Hz.
8) C5 and R14 prevent the output stage of the LM386 from oscillating at a very high frequency. The value of R14 could be as high as 10 ohms.
9) The LPF has a gain of 1.6 for the equal-value filter to work properly.
10) The circuits are very common and simple.
11) A HPF would attenuate the desired low frequency heartbeat sound. The very small value for C2 in the original defective project was a HPF.
12) The LM386 was chosen to drive low-impedance earphones to an adequate volume, with fairly low supply current and still operate well when the 9V battery voltage drops to 6V.
You wouldn't need more power to drive earphones, and speakers would cause acousical feedback.
The preamp can drive a load of 2K ohms or more. Therefore the input resistance of a power amplifier must be 2K or more, which has nothing to do with its output power.

Additional answers:
1) A preamp amplifies a very low-level signal to a line level without adding noise or distortion. Phonograph pickups also use a preamp.
2) You can boost (amplify) voltage or current. If both are boosted then power is increased.
3) A buffer has a high input impedance and a low output impedance. It prevents a low resistance load from loading down a high resistance source.

 

[hakyman]

Hey Audioguru You did again
thank you so much for your kind and quick reply again
i dont really know how can i thank to you thank you so much i'am gonna out of city for a week time. so i ll send the LF353(jfet) setehescope with a LM386 amplifier after i came back. see you
thanks for all

 

[hakyman]

hi audioguru. how r u
do you remember u recommended using a peak detector and a rectifer circuit to me to fix the output for an ADC. i tried so many times the peak detector circuits and i cant get the reason for using it. i use a adc0804. and the peak circuit just do the sampling duty like the ADC circuit can make it own. if i change the capacitor values of peak detector(change time duration) the circuit only help to find the max. peak of a cycle. and may i ask which point is the best for taking output to ADC.is the output point of amplifier(LM386) or output of the filter part. which one should i use. my amplifier(lm386) output is about 4.2V without a sound in the mic(change with the volume control pot.changes and it can up to 4.5V). and it swings with a heart sound around 4.2V(about 3.7-4.8) could i use the ADC directly and last one thing i use the 5.th pin of LM386 for output taking before 1000uF which its anot goes to headphones jack.
this is all i am very dogged to get the knowledge. if u can send me a circuit or just a block diagram i'll be so much happy and thanksfull. i search so much but i cant understand the death points of the circuits that help me find the circuits how to work. may be my english is not sufficient or may be their english is worse than me
whatever thanks already.

 

[audioguru2]

Hi Hakyman,
I recommended a peak detector rectifier circuit to provide only a positive single pulse to your ADC during each heartbeat. The earphones output swings positive and negative and the negative voltage swings will damage your ADC. The direct DC output of the LM386 could swing up to 8V which could also damage your ADC unless you reduce it with a 8:5 voltage divider.

A simple positive peak detector circuit is attached. Connect its input to the earphones output of the Electronic Stethoscope-2 project. The ADC's input resistance must be at least 330K. R2 in the detector circuit can be reduced to reduce the length of its output pulse.

View attachment 36470

 

[hakyman]

thanks for the advice

 

[loveguru]

hi,audioguru,
thanks for reply.i got the ic TL072.But i dont no the difference between dual opamp and odinary opamp.

i 've linear volume controller.you had suggested me to convert it to logarithmic by joining 3.3k resistance from slider to ground please give detailed idea about it.

i have an adapter which can supply 9 v in our circuit.you have used 2 9 v batteries if i want to use my adapter then what should i do?

what is varoboard?can i make this circuit on pcb?
waiting for your reply,
loveguru.

 

[audioguru2]

Hi Loveguru,
1) I'm glad you got a TL072 which has two low-noise, low-distortion and wideband opamps inside, instead of the TL071 which has only one low-noise, low-distortion and wideband opamp inside. They cost about the same and also about the same or less than a noisy, distorted and narrowband old 741 opamp.
The TL072 is used for opamps U1a and U1b in the Electronic Stethoscope-2 schematic.
2) To make your 10K linear pot (used for R11 on the schematic) act similar to a logarithmic (audio taper) volume control to match your hearing, connect a 3.3K resistor from pin 3 of U5 to ground.
3) You need two 9V power supplies for this project. One for the positive 9V and the other for the negative 9V.
4) Veroboard (also called stripboard) has strips of printed copper running in one direction spaced 0.1 inches like the pins on ICs. The board is also perforated all over in a 0.1 inch grid. I use it for prototypes and for small quantities of circuits.
You can make the circuit on a PCB if you want. I am sorry that there isn't a PCB artwork and layout.

View attachment 36503

 

[loveguru]

HI.AUDIOGURU.I HAVE STARTED TO MAKE E-SCOPE-2.
ON MY IC ,IT IS WRITTENED"TL072CP".
IS IT OK???????????
PLEASE REPLY ME SOON.
AND ALSO TALL ME THE DIFF. BITWEEN THOSE 2.
BYE.


LOVEGURU.

 

[surajbarkale]

It should be ok 'C' indicates commertial range & 'P'/'N' indicate package type (I believe P stands for Plastic & 'N' for ceramic). If you get hold of datasheet these differences will be mentioned.

 

[audioguru2]

Hi Loveguru,
They are the same. Your TL072CP is fine.
TI used to call the plasic package "N", but now call it "P" like everyone else. Some of their parts in plastic packages still end with "N" like the TL074CN. It looks like all their 14 pins plastic packages end with "N".

 

[loveguru]

HI...AUDIOGURU....
THANX 4 REPLY.
LOVEGURU.

 

[loveguru]

HI..............SURAJ.........THANX 4 REPLY.


LOVEGURU.

 

[Con1]

Ones I tried to build an Electronic Stethoscope from Elector electronics magazine with no luck. ???
Now, it is about time to build the E.S.-2 from Audioguru and see what happens.

For those how would like to build the Electronic Stethoscope

 

[Con1]

the pic of E.S. - 2

View attachment 36546

 

[audioguru2]

Hi Con,
That's a nice PCB. Please make a circuit and tell us how it works.
Where did you find a logarithmic (audio taper) trimpot for R11? All trimpots I've seen are linear.