Electronic Stethoscope 2

[solycutema]

hey.. thanx audioguru..

now it works... meaning there is sound output.... but theres a contanst *tick-tock* sound when the power is turned on. meaning.. my led will blink twice evry other second even without me talking into the mic,... when i touch the mic... it will have sound output... but rather noisy..

 

[audioguru2]

now it works... meaning there is sound output.... but theres a constant *tick-tock* sound when the power is turned on. meaning.. my led will blink twice evry other second even without me talking into the mic

Maybe your batteries are old with a high internal resistance which causes the supply voltages to jump around. Try new 9V alkaline batteries.
Does the blinking stop when the volume control is turned down?

when i touch the mic... it will have sound output... but rather noisy..

You are not supposed to touch the mic because it responds to very low frequencies and it is extremely sensitive.

Did you try connecting a speaker to the headphones jack? Did the project then make acoustical feedback howling?

 

[solycutema]

dear audioguru...

i dun think its the batt.... it still has 7V+.. =)
volume min = LED flashes fast
volume max = LED blinks steadily.... blue then red... blue then red.... (tick-tocks)

i attached a speaker... theres sound... no howling..... (ticks tocks)
i attached headphones... very loud *tick-tocks* according to the situation above..

*puzzled*

 

[audioguru2]

7V for a 9V battery and with the low current of this project is a battery that is wearing out. When it reaches 6V then it is dead.

Did you connect everything together with the "ground" symbol on the schematic?
Did you connect everything together with the "+9V" symbol on the schematic?
Did you connect everything together with the "-9V" symbol on the schematic?
Did you substitute any parts?

Please measure and report here the DC voltage measurements to ground of the microphone, pin 1 of U1, pin 7 of U1, pin 6 of U4 and pin 5 of U5.
Please look at the connections and parts values on the schematic again.

View attachment 39708

 

[mvs sarma]

Hi

Recently I saw one circuit of steth with pizio buzzer element (two tagged) as sensing element.

 

[taiebeh_mostajabi]

Hello
I couldent hear heartsounds,I think that the problem is the mic that I used,
I used very ordinary capacitor microphon but a small one beaucase I put it
to the sleeve rabber of stethoscope,
I want to ask what is the electret mic exactly (in electronic stethoscope 2)?

 

[audioguru2]

The electret microphone is polarized so its terminal that is connected to its metal case is ground.
The project needs a two-wires electret microphone from a toy or from a telephone. A three-wires electret microphone needs a different circuit.

Maybe you have a condenser microphone. It is different than an electret microphone because it needs a 48V external power supply to bias it.

 

[taiebeh_mostajabi]

I am sure that my microphone is biass in this circuit,beaucuse befure this circuit,I test Electronic stethoscope circuit , I could hear my sounds in 8 ohms speaker,but there were so much noise that I couldn t hear heartsounds .
after that I test electronic stethoscope 2 , I couldn t  hear my sounds(I mean my speaking sounds) and I couldn t hear heartsounds too but I put the stethoscopehead  on my neck and I could hear some frequencies and when I rub stethoscope I coud hear it sounds,so I thing my problem is mic,(it has 2 wire) :'( ???
maybe there is problem beetwin mic and stethoscope head,Should I past and press them togather ?

This is very urgently,I should finish it next week.
thanks.

 

[audioguru2]

I took a thick plastic lid from a jar and drilled a hole in its center for my electret microphone. Holding it up I could hear the low frequencies clearly in my earphones when somebody spoke fairly far away. When I pressed the jar lid to my chest so that the microphone has a small air space from it to my skin then the surround part of the lid blocked background noises but the microphone picked up my heartbeat loud and clear. The volume control adjusted the sound to be nothing or to be loud.

You must use earphones not a speaker to avoid the microphone hearing the speaker and causing acoustical feedback howling noise.
You must use shielded audio cable to connect to the microphone to avoid mains hum pickup.
Did you substitute any parts?

 

[Polybaci]

Hello!

Thank you, very nice schematic; I have built it and I hope it will be very useful as my wife is pregnant and we hope to hear the baby

View attachment 40273

View attachment 40274

 

[solycutema]

hi again,

i have problem with the circuit i just bulit. the batt turns very hot in like 15 seconds right after i connect the batteries. can help me solve this problem? wat r the possible errors? pls help.. thanx.

 

[solycutema]

7V for a 9V battery and with the low current of this project is a battery that is wearing out. When it reaches 6V then it is dead.

Please measure and report here the DC voltage measurements to ground of the microphone, pin 1 of U1, pin 7 of U1, pin 6 of U4 and pin 5 of U5.
Please look at the connections and parts values on the schematic again.

The DC voltage for the points : pin1 U1 = 6.9V, pin7 u1 = 7.3V
Pin6 U4 =8+V , pin5 U5 = 7+V

 

[audioguru2]

Hi Soly,
Is your negative battery getting hot because something is shorting it?
Your voltage readings are all too high and are positive which looks like the negative 9V supply voltage is missing.

 

[solycutema]

Dear Audioguru,

Is it ok if i use a 9V DC supplY? Used up many batts during the process of trials.. Cant afford too many.. =P

I am also using a 6 pole switch... where only 4 are being used. i use it to seperate the positive n negative voltage.  is it ok?

Am fabricating a new PCB in a few daes time. My previous attempt failed me... too small to solder my parts... many short circuits. *sigh*

are u able to check my pcb for me if i upload here? hope to hear from u sooon. thanx.

 

[audioguru2]

Is it ok if i use a 9V DC supply?

Yes and it doesn't need good regulation if its filter capacitors are big enough for low ropple.

I am also using a 6 pole switch... where only 4 are being used. i use it to seperate the positive n negative voltage.  is it ok?

Omly a 2-pole switch is needed to turn off both batteries.

Post a new pcb and I will check it for you.

 

[solycutema]

these are the pics of my PCB. the batts are replaced by DC supply. thank you for helping.

View attachment 40439

View attachment 40440

 

[solycutema]

Dear Audiuguru,

1) How do i know if i'm using a linear trimpot?
2) Can i still add the 3.3k resistor at pin 3 to gnd of U5 if it is already a linear trimpot?
3) Are there any other resistors on this circuit that i can change to trim pots in order to    change its functions/variability?
4) Can you help me design a circuit whereby i can use a switch to switch to it? with C3 and C4 at 4.7nF in order to hear lung sounds? is it hard to change from my already done PCB? means i can swith from circuit A to circuit B by using a switch. Switching from low frequency to higher frequency without another whole new circuit. jz a switching device.

hope to hear from  u soon.. need to finish by this week. =)

Thanx.

 

[audioguru2]

Hi Soly,
Your pcb is correct but you have the same size for a small 4.7uF electrolytic capacitor as for huge 470uF and 1000uF ones. The big ones will not fit.
You show all metalized plastic capacitors as round (they are rectangular) and with only 0.1" between wires (they have 0.2" between wires). Maybe you will use Oriental "green caps" and I have seen reddish coloured ones. They are also not round and their leads spacing is about 0.2".

1) How do i know if i'm using a linear trimpot?

Oriental ones marked A are logarithmic, B is linear. Turn it to halfway and measure its resistance from the slider to each end. A linear pot will have the same resistance from the slider to each end. A logarithmic volume control will be a low resistance to one end and a higher resistance to the other end.
 

2) Can i still add the 3.3k resistor at pin 3 to gnd of U5 if it is already a linear trimpot?

Yes, it will help make the linear pot more like a logarithmic one if the value of the pot is from 10k to 20k.

3) Are there any other resistors on this circuit that i can change to trim pots in order to  change its functions/variability?

I don't think so.

4) Can you help me design a circuit whereby i can use a switch to switch to it? with C3 and C4 at 4.7nF in order to hear lung sounds? is it hard to change from my already done PCB? means i can swith from circuit A to circuit B by using a switch. Switching from low frequency to higher frequency without another whole new circuit. jz a switching device.

Make a small pcb for two C3 values and two C4 values. Connect it to your main pcb and to a switch. Use short connecting wires.

 

[solycutema]

Dear Audioguru,

Thank you for the reply.
Can you draw the schematic of the extra circuit? I'm not sure how to connect the two diffeerent values to the main PCB and with a switching function.

Hope to hear from you soon. Thanx.

 

[audioguru2]

Hi Soly,
Connect a switch to two values of filter capacitors like this:

View attachment 40441