Electronic Stethoscope

[audioguru2]

Hi Dazza,
The LM358 has a minimum output current rating of only 10mA, typically 20mA. If your LM386 in the electronic stethoscope is driving two paralleled 32 ohm earphones to full output, it would draw about 72mA plus a few more mA for the opamps. The LM358 is a low power device but an MC1458 is two 741 opamps which aren't much stronger.
Measure the voltage of the positive supply for the LM386. I think you will see the voltage collapse whenever the LM386 is trying to produce output.

Re-install C7 and C8, they are important to stop the circuit from motorboating. Just use two alkaline 9V batteries, but don't short them this time.  ;D 

 

[steven2]

dazza read my posts seeking parabolic mike circuit  or other posts relateing to it theres a simple circuit that can hear heart beats to, in fact audio guru was very helpfull in helping me to increase the gain for it  this may help you with what you seek

 

[Dazza]

Hi Audioguru, steven

Audioguru, I have found that trial and error is the best way for me to learn electronics, I have had very little schooling and I struggle to get my head around the maths and theory :-\, in fact the only way I can write this post or any other, is with speech to text software.  I have found that first doing hands on projects and experimenting, makes it easier for me to understand the theory and maths .

The downside of using trial and error with this project is, trial and error = mistakes ;D = flat batteries = lets try that again = Oops that didn't work : = flat batteries = lets try something different = flat batteries = $$$ >.

This is my first audio project and my first project using a (+ - Gnd) and I'm learning a lot and very much enjoying it , so I will definitely take on some more audio projects in the future, but before I take on my next audio project, I'll have to put together a decent PSU with + - Gnd.

But for now it would be nice to be able to power this project from my existing PSU ???, which is the 0-30 Vdc Stabilized Power Supply, from our project section 8).

Thanks steven, I'll check that out .

 

[steven2]

dazza im suprised the top floor up stairs here hasent collapsed down onto the ground floor with the wieght of tons of electronics parts ive got upstairs , do you need any parts, its allso the main bedroom upstairs to  so i dont have far to go when i get out of bed  if i have any brain storm ideas to write down , my hydrogen generator still on hold pending on more ideas in the pipeline ,

 

[hakyman]

hi  Audioguru !!!!!
how r u ?for a long time later i come back
i finished the circuit and the matlab program to analyse the heart and respitory sounds.thank god anyway now i want to add a trnasmitter and receiver circuit because the cables really annoying hehe anyway what u suggest? i am searching for a simple, stable, and if possible without a needage of antenna hehe
do i want  so much things . i know i should write theese in another topic.but i want to get ur opinion . thanx
very very speciaal regards
ciaooooooooo

 

[audioguru2]

Hi Hakyman, welcome back. ;D
You can purchase a cheap wireless link that is made for a wireless mouse and similar stuff.
You probably must modify them with bigger coupling capacitors to get very low heart frequencies.
It is complicated to make a stable transmitter and receiver.

 

[Alun]

Yes you could have a go with the transmitter discused here: http://www.electronics-lab.com/forum/index.php?topic=2814.0 but you will still need an antenna of some description, the reciever is simple a normal FM radio will do.

 

[hakyman]

hi guys thanx for the replies
audioguru could pls make it some clear  cause i dont see ever a mouse kit with rf i only use IR kits. and do u know a link have some schematics without a needage of antenna of transmitter. u can write to the link to alun gave at  above where u discuss about transmitters . thanx very much
very very best regards

 

[e_isdyanto]

Hi, I'm a new one here. I think what u're doing here can be more useful if you always make some update. I've question to ask.
1. How do you can define which filter you want to use to measure is it heart sound or lung sound or other sound of the body? Heart, lung, ang other body-sound have different frequencies, what are they?
2. How much gain do you use in this schematic? And if I want to have gain 25x, which part should I change?
3. If I want to have a display and a microcontroller at the output, is it possible and how?
Thank you. I appreciate it if you can send your answer directly to my e-mail address, [email protected], thank you.

 

[audioguru2]

Hi E,
Welcome to our forum. ;D
From the tests that I have made, body sounds are like this:
1) Heart. An extremely low frequency DC pulse, sometimes modulated at about 25Hz.
2) Lung. Normal breathing and athsma squeaking is from about 300Hz to about 10kHz.
3) Blood flow. Probably also from 300Hz to 10kHz but my tests didn't have enough gain to hear it.

The project states the gain of its stages here:
http://www.electronics-lab.com/projects/science/019/index.html

You can't just pick a gain of 25 at random. The gain must match the amount of sound level and cannot be too high or the output stage will be noisy and distorted.
The project has a reasonable amount of gain that can be reduced with its volume control when required.

The project's output can be rectified and attenuated to match the input requirements of the ADC of a microcontroller. ;D

 

[xoy]

hi audioguru!!!!!

can you help me please improve this electronic stethoscope. i just want to make this elec-stetho to make it digital...

i want to connect a pulse counter on the bi-color LED, so that it will count the blinks of one LED. the counter will diplay the counted pulse on an 7-segment LED display. i also want to put a 60-seconds timed switch at the entrance of the pulse counter. this means it will stop the counting after 60-seconds to get the accurate heart rate.

next time i will attached my circuit. i dont knw how to edit the pic, coz were using redhat instead of microsoft word. thankss...

hope you can put attention on this....
any reaction are highly appreciated.....

----xoy------

 

[audioguru2]

Hi Xoy,
For my Electronic Stethoscope-2 project, people have said and my tests have shown that the LED flickers with some hearbeats. This will give too many pulses to your counter. Therefore the circuit needs an integrator (very low frequency low-pass filter) to feed the LED driver that feeds the counter.
If you don't need audio output then the existing lowpass filter can be set to a lower frequency by increasing the values of its C3 and C4 and also increasing the values of its R5 and R6.
If you do need the audio then another lowpass filter can be made like the U1b stage, with the values increased.

Maybe it would be best to time the pulses for only 6 seconds and shift the decimal point in the display to indicate pulses per minute.

I use Microsoft Paint to edit all pics. It is much easier than Microsoft Word. ;D

 

[xoy]

hi audioguru!!

tnx!!

maybe thats a good idea..

first, i have to ask.. does my idea really possible to make this digital?

does it mean i have to put another U1b stage. where should i place it?
another prolblem i have encounterd here is, the timer. for now i want to buy a kit of switch timer, but if you have one circuit of it , please post.
sorry,, but i dont iunderstand about that 6 seconds timer...


tnx!!!!

-------xoy-------

 

[audioguru2]

first, i have to ask.. does my idea really possible to make this digital?

Sure, if there isn't any friction noises then your idea will allow this project to display heatbeat rate.

does it mean i have to put another U1b stage.

Yes if you still need its audio output.

where should i place it?

The new R5 will connect to the exising pin 7 of U1b. Then U4 connects to its output. The U4 circuit will need to be changed so that its output doesn't exceed +5V and doesn't go negative.

another prolblem i have encounterd here is, the timer. for now i want to buy a kit of switch timer, but if you have one circuit of it , please post.

Use any timer circuit.

sorry,, but i dont iunderstand about that 6 seconds timer...

You can count pulses for a full minute, or count pulses for only 6 seconds then add a zero the the number counted for the results in one full minute. For example, a heartbeat rate of 100 beats per minute will be counted as 10 in 6 seconds. Adding a zero at the end results in 100. ;D

 

[xoy]

tnx audioguru!!!!

now i can start this....
i will notify you anytime for any improvements, problems, or anything...

i will use a an IC voltage regulator having an output of 5V.

wait.. i dont know how to trigger a switch using a timer to switch off the entrance input of the counter. i mean a timed switch...

i have my circuit to be.. but i can't upload it here using the bmp or paint..

thank you so much!!!

----xoy----

 

[audioguru2]

Hi Xoy,
Silicon Chip magazine has a heartrate monitor project. They use a sensor that detects blood motion in the skin with an LED and optosensor. They use a PIC to do the counting and drive to a 3-digit LED display. You can see the entire project for free if you enter into a Google search, Silicon Chip Heartmate. In Australia and New Zealand, kits might be available with the PIC already programmed.

The output of your modified Electronic Stethoscope-2 circuit should be able to drive its counter easily. ;D

 

[xoy]

hi audioguru!!!

long time no hear!!! hehe...

i just want to ask if the counter in (http://www.aaroncake.net/circuits/counter.htm),
would be compatible to the electronic stethoscope2 when tapped to the bi-color LED.

tnx!!!
have a good day!!!!

---------xoy------ ;D ;D

 

[audioguru2]

Hi Xoy,
That old counter circuit will work if you add another very low frequency lowpass filter so that it receives only heartbeats, I think I discussed it before. You also must use a Schmitt trigger device to produce pulses with rise and fall times much quicker than a 741 opamp can provide. You must rectify the signal and limit its output voltage to 5V so that the TTL counter isn't damaged. You must provide a regulated 5V supply for TTL.

You won't need to rectify the signal, nor use a Schmitt trigger nor limit the output voltage if you use a modern Cmos counter circuit operating on the same 9V supply as the Stethoscope-2 project. Of course you still need an additional very low frequency lowpass filter. Just feed the 741's output through a resistor to the input of the Cmos counter circuit. A suitable Cmos dual BCD counter is a CD4518. Suitable Cmos 7-segment display drivers are CD4511 or CD4543. ;D

http://focus.ti.com/docs/prod/folders/print/cd4518b.html
http://focus.ti.com/docs/prod/folders/print/cd4511b.html
http://focus.ti.com/docs/prod/folders/print/cd4543b.html

 

[xoy]

hi audioguru!!

tnx!! for the help....

but at as usual... pls help me again...

i cant find bi-color LED that has only two leads, what i only see is an LED which has 3 leads, it seems its not available here in manila, philippines.

is there any replacement for IC TL072?

i have thought that the kind of capacitors (C3 nad C4) used in the filter is an adjustable.. but it wasn't... is there anything to use which is an adjustable?

Maraming salamat po talaga!!!!!!! (I'm very thankful to you!!!!)

----xoy------

 

[proton1]

who can write a report of how it work?