Electronic Stethoscope

[Emad1]

hi Audiguru. I had no TLO71 in my area so I tried to use to use just one IC as apreamplifier and another one as an amplifier------- Just two . the preamplifier is LM358 and then the amplifier is the LM386 as that in your corrected circuit-------I hear my heart beats very well------- Ijust need trying another headphone as I expect sound to be better if I use an earphonr other than my mobile headphone. THats what I did . Thank you audaguru

 

[Emad1]

Audiguru. Iforgot to tell you that I took the LM358 from the shop and when Iwent home I found it KIA358 and I used it. This IC doesnt need a ground and so I used a single battery, just positive and negative

 

[audioguru2]

Hi Doctor Emad,
Did you use the KIA358 for both U1 and U2?
I checked, and a KIA358 is the same as an LM358, which is a dual opamp. It is noisy like a 741 and has crossover distortion because it uses very low supply current.
Can you get an NJM072B which is made by New Japan Radio? It is a dual low-noise opamp almost the same as a TL072. Don't use an NJM072 without the "B". They admit that they made a big mistake when they made that copy.
I do not recommend using only one battery because then you will need to add resistors and a capacitor to make a mid-supply voltage for R3 and R8 to connect to, as their voltage reference.
Use 2 batteries like my corrected schematic and hope that the noise and distortion of your KIA358 aren't too high.

 

[singhal_gauravad]

3. sir, what is the need of bi colour led. r we can make it
3. How do I connect a phone jack? Could I connect it to the speaker or ear phone? How to connect them properly?

Any help will be greatly appreciated. Thank you in advance.

Project Link: http://www.electronics-lab.com/projects/science/014/

 

[audioguru2]

Hi Singhal,
Welcome to our forum.
That project has errors and doesn't work. I have corrected and improved it and posted it here:
http://www.electronics-lab.com/projects/science/019/index.html

1) The bi-colour LED and the opamp driving it aren't necessary, it just looks nice. The bi-colour LED was chosen because it has two LEDs in one case with the LEDs connected in opposite polarities. Two separate LEDs of any colours would work the same. Each heartbeat causes the colours to indicate differently. Sometimes the colours alternate quickly and flicker, other times only one colour lights during each heartbeat.
2) Connect a "phone jack" properly by soldering short wires to it and soldering the wires to the circuit.
He, he. Yeah, the heartbeats make a phone dial for help! He, he. ;D
It isn't a jack for a telephone, it is called a "phone jack" because it looks like the jack telephone operators used long ago when they plugged-in your connection. Use a jack for home stereo headphones or the smaller jack for headphones from Walkmans or CD players. I recommend using cover-your-ear headphones to reduce hearing background sounds and feedback.
Don't use a speaker. It would produce loud squealing noise from acoustical feedback.

 

[MP1]

To all users on this thread....

...Actually some users reported that the Electronic Stethoscope worked and others reported that they could not make it work. I see there are several posts in the Electronic Stethoscope 2 topic now going both ways as well. It is normal to have users with different capabilities on a forum. Many will not be able to make a project, even with much help.

It should be noted that Audioguru designed the electronic Stethoscope 2 but he did not ever build it. It should also be pointed out that Audioguru did not build this project to verify that it would not work. Audioguru is a "Theory Expert" as it states in his signature.

There will be those who can build both and there will be those who cannot build both.

MP

 

[audioguru2]

This is only one problem of many with the original project.
There is no way a 741 opamp can work in this circuit without a negative supply for its pin 4 that some builders added after hearing about it.
There is also no way a 741 can provide enough current to drive an 8 ohm earphone or two paralleled ones.
There is also no way this 741 can amplify audio properly without any negative feedback. Its gain would be 5000 times too much.

View attachment 36576

 

[Dazza]

Hi,

I'm going to give this project ago, I want to use it to listen to my unborn child's heartbeat 8).

audioguru, could you please suggest some alternatives for the (LM386)and(TL072) if there are any suitable replacements.

Thank you .

 

[audioguru2]

Hi Dazza,
It is wonderful to hear that you are going to be a daddy!    ;D

The LM386 1/2W amp has been very popular over here. It is used in nearly every small radio or tape player, and wireless baby monitor that I have ever seen. I don't know what brands you can buy down under, but Philips and Motorola (now their consumer analog ICs are made by ON Semi) have suitable small bridged amps. Bridged amps don't need that big ugly output coupling cap:

Philips
http://www.semiconductors.philips.com/acrobat/datasheets/TDA7052_CNV_2.pdf
Its gain is fixed at 100 but can be reduced.
http://www.semiconductors.philips.com/acrobat/datasheets/TDA8541_5.pdf
Its gain is determined by two external resistors.

Motorola (ON Semi)
http://24.17.121.14/DataSheets/mc34119.pdf Its gain is also determined by two external resistors.

The TL072 dual low-noise opamp is also very popular over here and is used in almost every consumer product that has high quality audio, and nearly everything I make. There must be many alternatives but about the only one I think about uses triple the supply current and is also made by many companies (Philips invented it but don't make it anymore):
http://www-s.ti.com/sc/ds/ne5532a.pdf

Happy thumping!  ;D

 

[audioguru2]

Here's another European little amp IC: http://www.fieros.de/philips/tba820m.pdf

 

[Dazza]

Hi audioguru,

I have a listing in my Jaycar catalogue for a (LM386N-1) low voltage 1 watt amplifier.  And I just found in my junk box an (TL072) .

While I am away, I'm hoping to get the chants to visit a Jaycar electronics shop, there usually very knowledgeable,  unlike Dick Smith >, so hopefully they can offer me some solutions/alternative components for both my projects .

 

[bugz1]

hello someone know what is the frequency response of EM-80 electret condenser mic

Thanks  ???

 

[audioguru2]

Hi Bugzy,
Welcome to our forum.  ;D
Are you making the original Electronic Stethoscope project or the corrected and improved Electronic Stethoscope-2 project?
Most electret microphones have very good frequency response of from about 30Hz to about 15KHz and the response is fairly flat.
Whoever makes your EM-80 mic should have its spec's on their website.  ;D

 

[Dazza]

Hi,

I've completed this project, electronic Stethoscope 2 .  Either I'm expecting too much from this project , or more than likely I've made an error some where :-\.

I can hear a "very vary" faint but clear heartbeat, when I adjust the 10K LOG potentiometer to around its minimum, say less than a quarter of its wipe,any more than that and I get crackling coming through the headphones, also when I first applied power I heard nothing coming through the headphones until I adjusted the potentiometer to about half and then I heard motor boating through the headphones, I applied power again about an hour later and this time it worked.  I have experimented with different stethoscope heads and mikes, with very little improvement .

I use this PCB that someone posted and found that R8 and R7 were incorrect and needed to be swaped around, also I discovered that the positive and negative terminal connections are a dead short, so I connected them to negative of C8 and positive of C7, of course not before I flattened two 9V batteries : ;D, hopefully I haven't damaged one of the ICs, could this be why it's not working as well as I expected ???.

Now that I'm low on 9V batteries ;D, how do I power this project from my power supply, can I use two 9V regulators, how do I configure them ???.

View attachment 36851

 

[audioguru2]

Hi Dazza,
I'm sorry I didn't make a pcb for this project.  :'(
It's too bad the pcb shorts flattened 2 batteries and I see where its R7 and R8 are swapped.
I don't think the IC's are damaged by the batteries being shorted.

I think that the LM386 as U5 is oscillating when you turn up the volume. Its ground pin 4 and the load's ground are on the same pcb path as the input ground. U5 and the output ground should be on one path, and the input, preamp parts and the volume control should have their own path, to the junction of C7 and C8.

Also, U5's unused gain pin 8 is very close to its output pin 5's pcb path and R14. When not used, pin 8 can be considered as a positive AC input and at very high frequencies, around and around she goes. Try lifting pin 8 away from the board.

Did you use a ceramic disc cap for C5? It is important because the LM386 has a frequency response that extends out to 300KHz. At such a high frequency, the inductance of other types of caps, headphones or a speaker cause them to be a very high impedance.

You can use a power supply that doesn't need regulation, that is somewhere around positive and negative 6V to 12V.

The you can hear your unborn child, congrat's!  ;D

 

[Dazza]

Thanks for your reply audioguru ,

Yes, I did use a ceramic disc cap for C5. I had an idea that track placement would be important for this project, that's why I used the PCB pattern that a member posted, as I had no idea on correct track placement to design my own PCB, maybe I should give it a go, I will have to start by redrawing the schematics as I find it difficult to follow the way it is drawn, then I will need to post it for inspection to be sure I got it right, before having a go at designing a PCB, Mr Audioguru Buddy old Powell ;D, can you inspect my redrawn schematics once it is done and then the many attempts that I'm likely to make, at designing a decent PCB for this project ???.

Can you tell me which track placement are important, as I said I have no idea but I'm willing to have a go , I'm sure others would appreciate a PCB for this project .

This is the first time my partner has taken an interest in one of my electronic projects, she spent ages with it trying to hear our unborn child's heartbeat, even though it was barely working ;D.  At our last checkup at the hospital they used a small handheld electronic stethoscope to listen to the babies heartbeat, it was just amazing to hear our babies heartbeat and that was what made me keen on making my own electronic stethoscope .

This will be our second child, our first is nine now our daughter, and it really is no less exciting then the first 8).

My partner had some very serious medical problems, not long after our daughter was born, as a result we didn't believe it possible to have another baby and in fact it is somewhat risky, for both mother and child and the medication that my partner must take ads to the risk , I think it would be very reassuring to be able to hear our babies heartbeat throughout the pregnancy .

 

[audioguru2]

Hi Dazza,
Sure I will help you on this project.  ;D
Please don't give-up on the other member's pcb yet. I am only guessing that U5 is oscillating, maybe something else is wrong.
1) Measure the DC voltage at the microphone. With a 9V supply, it should be between +2V and +7V.
2) Measure the DC voltage at pin 7 of U1B. It should be less than about plus or minus 30mV.
3) Measure the DC voltage at pin 5 of U5 with the volume control turned down. With a +9V supply, it should be between +4V and +5V. Turn up the volume and see if it changes.

Cut the ground trace at the edge of the board between the volume control and U5. Then connect the ground of the mic to the junction of C7 and C8. Maybe that's all it needs to fix it.  ;D 

 

[Dazza]

Hi, audioguru and Thanks for your help,

(1) DC voltage at the microphone    (4.80V)
(2) DC voltage at pin 7 of U1B      (  03.9mV ) 
(3)    the DC voltage at pin 5 of U5 with the volume control turned down (4.19V) and with volume control turned fully on, it continuously changes between about (4.07V) and (4.22V)                                                                                             

I made the changes you suggested and it improved maybe a little.

The crackling only happens when I hold the stethoscope head to my skin, and when I hold the stethoscope head in the air I can hear the sound of the TV in the background, and the strength of the sound does rise and fall with the volume control.  I did use 10V caps for C6 and C7 could this have cause any problems? I was at first convinced that it was the stethoscope head I was using, so I did try several different ones with no improvement :-\.

 

[audioguru2]

Hi Dazza,
Your voltage measurements are perfect.

 

[Dazza]

Hi Audioguru ,

I've attached a sound file of exactly what I am hearing while listening to my heartbeat, while adjusting the volume control from minimum to maximum 8). As I adjust the volume control from its minimum I can just make out but barely hear my heartbeat it is very vary faint, with no distortion crackling or friction noises, if I adjust the volume control any more than about less than quarter, the distortion and crackling cuts in .  I've tried using large plastic jar lids and metal lids of all different shapes and sizes with the same results, the stethoscope head I used for the recording is a very small metal jar lid with a small hole drilled in to it, to pass through the shielded cable, then I used a thick amount of hot glue to secure the Mike to the inside of the lid, then I coded the entire lid with a thick layer of hot glue including the rim that would come in contact with my skin, then came the fun part ;D ;D, I smeared some olive oil on my chest and still it didn't make any difference ???.

HART_1.zip