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Electronic Stethoscope 2


Emad
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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
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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.

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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.
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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.

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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.
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Dear AUDIoguru,

Thanx for the input.

These are my measured voltage:
TL072 Pin 4 = -7.2V
          Pin 6 = -0.08V
          pIn 7 = -0.12V
          pIn 8 = +0.07V

LM386 Pin 1 = +1.5v
          Pin 5 = +1.9V
          Pin 6 = +2.7V
          Pin 7 = +0.2V
          Pin 8 = +0.2V

UA741 Pin1 = -6.9V
          Pin2 = -0.43V
          Pin3 = -0.5V
          Pin4 = -6.7V
          Pin5 = -6.9V
          Pin6 = -0.47V
          Pin 8 = +0.34V

When i plugged in the DC supply, LED blinks contanstly. I hear buzzing sound continuously through the headphones. when i tap on the electret mic, the buzzing sound will tap also. what problem am i facing? pls advice. thank you.

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Hi Soly,
Your circuit doesn't have a positive 9V supply:
Pin 8 of the TL072 is supposed to be +9V. Yours is nothing.
Pin 6 of the LM386 is also supposed to be +9V. Yours is very low at only +2.7V.

The above pins are connected together and should measure exactly the same voltage. Yours have different voltages.

Your -9V supply measures -7.2V on pin 4 of the TL072 but measures only -6.7V on pin 4 of the uA741. They are connected together so they should measure exactly the same voltage. Yours have different voltages.
It should be closer to -9V.

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If my PCB connections are correct, what maybe wrong?

Pin 8 of the TL072 is connected to pin 6 of the LM386 on your pcb and is labelled "+9V" correctly. You measured different voltages so maybe the printed copper track is broken. Measure the copper with an ohm-meter to see where it is broken.
Measure the voltage of the positive battery while it is powering the circuit.

Pin 4 of the TL072 has a jumper wire to the -9V battery and pin 4 of the uA741 also has a jumper wire to the -9V battery but the voltages measured different. Measure the resistances of the copper track and the resistances of the jumper wires to see where it is broken.

If the Microcontroller are faulty, would it cause the different voltages?

Maybe the microcontroller or its voltage regulator is shorting the +9V battery.

Is it ok if i supplied more than 9 Vs?

Look at the datasheets for its ICs. The max supply voltage for the LM386 is 15V.

how to check if my ICs are faulty?

They are cheap. Replace them to see if one is bad.
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Dear Audioguru,

You were right when u said that the voltages are missing.

I'm using DC power supply. I can't seperate the positive voltage and the negative voltage. From the DC male jack to the female jack, with a multimeter, i can get both the +ve and -ve voltage. But once i connect the two ends [the end that connects to com port on multimeter], the voltages reduced to 0.2volts. Why is that so? Pls help. Thanx.

p/s sorry for troubling u this few daes. =)

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I'm finished working the ELECTRONIC STEThoSCOPE 2 project and its working just fine. now all i need to do now is to put or connect a 7 Segment LED  heart beat Counter circuit display to count in heart beats. but can i put or connect a 7 Segment LED Counter circuit to the ELECTRONIC STEThoSCOPE 2 even without changing the original circuit config. of the ELECTRONIC STEThoSCOPE 2? and is there a 7 Segment LED heart beat Counter circuit display project posted in the forums?

Please help!

any replies regarding to this topic will be highly appriciated! Thank you!

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Hi Greg,
I am glad that your project works well. ;D
It uses unregulated 9V supplies which will be fine for a Cmos counter circuit. A TTL counter circuit would need a 5V low dropout regulator and a few other parts.

The AC signal from the output of U4 could feed through a 10k resistor into 1/6th of a Cmos Schmiitt-trigger inverter to convert the AC into clean pulses then a second inverter could be used for you to select the best pulse polarity for the counter.

We have a 99 seconds timer project that has a Cmos counter:
http://www.electronics-lab.com/projects/oscillators_timers/014/index.html .
Its clock can be the heartbeats and you would need to make your own timebase gating for it.

There is a heartbeat display project on the web that used a microcontroller for its counter:
http://www.web-ee.com/Schematics/HeMon/HeMon.htm .

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I've had a terrible time trying to get this circuit to work on a breadboard.  The most I've had it do it make a faint noise when I put the headphones in.  I think Im putting the last section together(U5).

Just ordered some vero board, i know where I am when Im soldering :) 

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Hi Philipf
I made both the stethoscopes the one with the 5 741 op-amps doesnt work at all but the stehoscope2 by Audioguru works really well. I took it to class and all the students liked it. It is much easier to listen to a heart beat than with an accoustic stethoscope

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Hi Greg,
I am glad that your project works well. ;D
It uses unregulated 9V supplies which will be fine for a Cmos counter circuit. A TTL counter circuit would need a 5V low dropout regulator and a few other parts.

The AC signal from the output of U4 could feed through a 10k resistor into 1/6th of a Cmos Schmiitt-trigger inverter to convert the AC into clean pulses then a second inverter could be used for you to select the best pulse polarity for the counter.

We have a 99 seconds timer project that has a Cmos counter:
http://www.electronics-lab.com/projects/oscillators_timers/014/index.html .
Its clock can be the heartbeats and you would need to make your own timebase gating for it.

There is a heartbeat display project on the web that used a microcontroller for its counter:
http://www.web-ee.com/Schematics/HeMon/HeMon.htm .


Thank you so much Sir! those things could really come in handy! but i dont really need a timer circuit, i just need a heart beat counter display. http://www.web-ee.com/Schematics/HeMon/HeMon.htm  :) i'll post a reply as soon as i have improvements.
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