Electronic Stethoscope 2

[audioguru2]

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?

 

[steven2]

good stuff audio guru wheres the circuit for the other stage for the cir-am002gif. and the other circuit wheres the other part so they will be complete

 

[audioguru2]

Hi Steven,
What is cir-am002gif?
What circuit, what other stage, what other circuit and what other part?
What will be complete? Del's burglar alarm? ??? ???

 

[mannyt01]

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

 

[audioguru2]

Hi Manny,
Welcome to our forum.
I am sorry that your 2nd project didn't work. We can troubleshoot it with voltage measurements, etc. if you wish.

 

[steven2]

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 ,

 

[audioguru2]

Hi Steven,
A few people have built it and reported in these posts that it is successful.
This one doesn't work because it has wires shorting or in the wrong place.

 

[steven2]

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

 

[audioguru2]

Thanks Steven (Sparky),
I look forward to reading about and seeing pics of your big sparks!

 

[steven2]

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

 

[steven2]

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

View attachment 36324

 

[audioguru2]

Hi Steven,
I am sorry to say the circuit won't work the way you changed it:
1) You have the volume control connected to pin 7 of the TL072 which is the output of its 2nd opamp, but that opamp's input at pin 5 is not connected to anything. For your "big ear", you don't need the low-pass filter which consists of U1b (you could use a TL071 single opamp for U1a if you change all of its pin numbers to match), R5, R6, R7, R8, C3 and C4. All those parts can be replaced by a piece of wire from pin 1 of the TL072 to terminal "a" of the volume control.
Disable U1b by connecting its pin 5 to ground and connect pin 6 to pin 7.
2) You don't have a negative 9V battery (Batt 2) connected to pin 4 of the TL072. It certainly won't work without it.
3) You don't have the battery bypass capacitors C7 and C8. The circuit will probably "motorboat" without them when the batteries run down a bit.

Then you will have a very simple circuit with U1a used as a low-noise microphone preamp, and U5 (the LM386) used as a headphones driver.

You know what? My son has a spare 61cm diameter satellite dish. I'll try my electret mic mounted in its focal point. Its diameter is much larger than the horn from your PA speaker so it should have very good pickup of distant sounds.
The trouble with it is that it is made of steel and is kinda heavy to carry around.

Since we have changed the topic, please open a new post in our forum "Electronic Projects Design/Ideas" and call it "Big Ear Microphone circuit" or something.

 

[steven2]

did i make a few erors when i redrew your circuit audio guru i posted a big ear circuit recently but it suddenly stoped working again, it used to work good but i had to use a radio to receave it but id rarther something that can do it without the transmitter

 

[hakyman]

hi audioguru. i need to ask that the output of the circuit is sufficient to apply to a adc circuit. could i transfer the output to a pc in digital format. i mean i want to monitor the output signal of this circuit on pc. and second question; can i add a power amp circuit to output of this circuit to amplify better (like lm1875). is it possible? thanks alot already. ihope i can explain my questions well
sorry for the bad english

 

[hakyman]

hi again. audioguru u wrote the cutoff frequency of LPF is 103hz but i read that the heartsound frequency range is 20 to 200 hz. and for medical care the cutoff should be 600hz(for listening lung etc.) what do u think?
i'd like to say smth about the lm358 circuit i built it up and i get a weak sound (from a 4ohm hop.)but no noise then i connected its output to a amplifier lm1875 but i couldnt get an output what could the reason is? could anyone send a amplifier circuit for lm358 pre amp circuit? and last one thing what kind of ecm is used i use a electret mic has very low value.
thanks much

 

[audioguru2]

Hi Hakyman,
Welcome to our forum.

1) Your ADC probably has an input voltage range of 0V to +5V. The output of the Stethoscope-2 project swings about +3.5V to -3.5V. If you use the output pin of the LM386, the voltage will swing about from +1V to +8V, no longer negative but still too high for your ADC. Therefore if you attenuate it 8:5 with a 2-resistor voltage divider it will be fine.
You may want to use an active full-wave-rectifier circuit with a peak detector filter so that the signal to the ADC is a heartbeat pulse instead of the very low frequency vibration that is heard with headphones.

2) The output of the project is such a low frequency of from 16Hz to about 30Hz that you probably won't find speakers good enough and big enough to reproduce it. If you did use very good speakers then they probably must be located in another building to avoid acoustical feedback. The isolation of the mic is poor at very low frequencies.
Fairly good quality headphones sound fine. I used the "on the ears" headphones that came with my Kenwood portable CD player. Similar Sony headphones also sound fine. "Covering the ears" headphones would be best.

3) The cutoff frequency of the LPF is chosen to allow adequate heartbeat sound and adequate attenuation of background sounds such as people's voices. In the project, substitute LPF capacitors are discussed to increase the cutoff frequency to 1KHz to hear respiratory (lung) sounds. You could use a switch if the 1KHz cutoff frequency picks-up too much background sound when listening to heartbeats.

4) I have never recommended an LM358 circuit. It is too noisy for amplifying a microphone. I recommend using the low-noise TL072 dual opamp. Maybe you tried the LM358 circuit posted by Doctor Emad that has problems. Maybe your LM1875 didn't amplify it because of those problems or because capacitive coupling to your amp wasn't used.

5) I made a quick test with an electret mic from a cell phone, it worked well. Nearly any 2-wire electret mic will work in this project. They cost very little. My Newarkinone (Farnell) catalog lists about 20 having different sizes, with similar spec's and prices.

 

[hakyman]

Thank you so much audioguru for your kind and quick reply. i get the components. i'll share my experiments with you when finished and then ill add the circuits to apply an ADC circuit and try the output convert in digital. Thank You so much again...

 

[hakyman]

hi again i built the circuit but it seemed not so good. the filter part seems ok when i give a sound like sssssss it not sense to this but i gave a bass sound like boooo yeah it give an o/p. but when i heard a sound its have pıt pıt pııttpı i cant understand what it is and it get louder when i gave a louder sound(give my breath it has no sense to all standart voices in speaking). this result same in both a 4ohm 5W hop. and with a sony headphone(ear-in i havent get a earcover one yet). the reason is the load(hop or headphone)? and i only had a o/p stage as -/+ 1.5 V max. when no input(no sound) the o/p swings between +/- 20mV at this time my pot adjusted to 1.9K. i used a 5K pot no form as 2,5K pot in my land and i dont think it'll effect but if yes i can change it with a 2K pot . i took all leads as short as possible(the mic lead is about to 10 cm). any change or correction on circuit? pls help me who work it with no problem . i remember doctor emad and audioguru succesed.thanks for your helps again ...

 

[hakyman]

i' really sorry i forgot smth. i connect the mic to the stethescope's one ear. i couldnt cut the tube cause it is littmann and so expensive ;D whatever i got the heart sounds so clear but it has pıt pıt in the heart sounds i dont know how can i explain. it sounds like more sharp. i wish you get me audioguru what i mean. and its harmfull to my ears when i touch wrong place of steth. i get all the diaphram sounds and its really annoying, my ears ache cause of that. and last thing ;do i need offset the TL072 it has a null pin but some differences with 741 and i dont know sould i or how i do.
thats all i know i ask so many questions but this is important for me i struggle to do the best. im sorry so many many thanks again wait for answers...

 

[audioguru2]

Hi Hakyman,
Happy New Year.
1) Did you build the Electronic Stethoscope-2 project or the original project?
2) What is a " pıt" sound?
3) What is a " 4ohm 5W hop"? The LM386 is not designed to drive a load impedance less than 8 ohms, it may be damaged by excessive output current or overheat.
4) The volume control can be any audio-taper pot between 2K and about 50K.
5) You shouldn't hear a loud sound when you touch the stethoscope head. Maybe you are hearing mains hum caused by the electret mic connected backwards so that its ground terminal is connected to the circuit's input.
6) The circuit doesn't need offset voltage nulling since the circuit's U1a plus U1B opamps have a DC voltage gain of only about 1.6. The LM386 also has a low DC voltage gain. The TL072 dual opamp doesn't have offset-null pins, just 3 pins for each opamp plus positive and negative power pins. The TL071 single opamp has the same pins as a 741.