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digital elec-stetho..


xoy
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hi audioguru!!
tnx....

1.) you have told me before (page 13, reply #170 and #172) to add another Ub1 stage to detect only the exact heartbeat pulses... so maybe the problem about the numerous pulses is out...

2)  i have here again the circuit... i add the schmitt trigger that turns the analog signal into digital signal. .(http://www.play-hookey.com/digital/experiments/rtl_schmitt.html)

3.)  also include the circuit from the timer......       
                (http://www.electronics-lab.com/projects/oscillators_timers/015/)
.....to transform it into a counter,  problem is.. ??? i dont know in where pins of cd4518 should be the input signal, be placed.
***if i add another display... how??

tnx again!!!
----XOY----- :) :)

 

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  • 2 months later...

hi audioguru, alun, and other eletcronic gods there....

i know this is another topic to be discussed in the part of electronic stethoscope so why i build this new page...
due to financial problem, i was seldom replied in some of of my discussion about some of my questions.. in the other page of electronic stethoscope.. so i just wanted to focus here,,

here is the situation, i just wanted to have sure answers.. althuough audioguru have help me a lot, i cant still understand because of i have lack of knowledge about this..
i was preparing for my project to build a amplified digital stethoscope..
due to lack of knowledge, i am very please that you can show me a circuit or schematic diagrams... please help... i will be very very glad if you still continue helping me regarding this.. thanks....

1.  i just want to have the electronic stethoscope, to have an output on at   
      least a 1kilowatt amplifier and speaker. So that we can hear the sounds on
      our class.

2.  i just want to have this electronic stethoscope, which will display the heart
      rate (or heartbeat per 60 seconds). the dispay must be in 3 digits, because
      the heart rate may exceed over 100.  (hi audioguru, i am very interested on
      what are you trying to tell me regarding the 6 seconds, i just cant hardly
      understand it, but im near now to undesrtand it...)
      this is what you suggested me before regarding this..

      A 1 minute update on a stethoscope is a long time to wait and to see any
      change. You could use a 6 seconds timer for a quicker update, then add a
      zero to the display to show beats in 60 seconds.
      You could add a phase-locked-loop with a digital divider to multiply the
      frequency of the beats per minute, then display them accurately in beats per
      0.6 seconds, updated every 0.6 seconds.
      i really like the idea, i just cant hardly understand it without any circuit.. but i
      know this is quite feasible..

      Can you plaese post at least a circuit of this, regarding to my counter ciruit.

3.  i just wanted to have this electronic stethoscope to have another back-up
      supply. A 9VDC AC adapter will be used as the other supply, with the two 9V
      batteries. When the 9VDC AC adapter is used, the connection of batteries will
      be automatically cut-off, so that it wont supply.
      ive got the answers of this at the page of electronic stethoscope. but what i
      dont know is when i use the 9VDC AC adapater, how could the connection be
      automatically connected to the 9VDC AC adapter, and automatically
      disconnect to the batteries.

      here i will post a circuit, please edit. Please take out what is not needed, just
      add if there is needed.. just coerrect it please... any help are vere highly
      appreciated.. plase help
      thanks...






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I'd use a microcontroller to count the time between the heart beats and from that calculate the number per miniute.

Good idea! It could also perform the entire counter.

you could use one AC-AC adaptor (a transformer built into a plug) to power a simple voltage doubler that'll give you a bipolar (positive and negitive) supply.

Another good idea! If you don't use the 741 and its LEDs, the negative supply's current is only about 2.5mA.

until you've mastered the basics, try building some or the more simple projects on this site before you try this one.

Well, the stethoscope project by itself is fairly basic and simple. Instead of adding a complicated display of beats per minute, you could make it beep. Then the beep can be amplified and everyone could hear it. ;D
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  • 1 month later...
  • 2 weeks later...

hi again!!!

i ask my teacher for that beeps, but he is really forcing me to have an output in an LED display..

i have simply just design two circuits here, but this really needs any corrections...
can you please help to get through this... thanks!!!
i get the circuit of the counter and the timer on
(http://www.electronics-lab.com/projects/oscillators_timers/014/index.html)
and (http://www.electronics-lab.com/projects/oscillators_timers/015/)..

i also add another Ub1 stage to pass the heart beats sounds only...

tnx in advance.... merry christmas!!!!!!

------xoy----

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  • 2 weeks later...

thanks audioguru...


now i can have a better discussion with you now...

answer at #1: you adviced me before to have a 2nd Ub1 stage, so i put it after the first Ub1 and before optional stage...

answer at #2: i use trimmers intead of resistors so i can easily adjust the frequency..

answer at #3: it is already connected to the ground of the optional stage..

i have tried to connect the input of the schmitt trigger to one of the LED so that only the thomping will be counted and not the thumping... (thomp-thump)

answer at #4: i have seen so many rectifier circuit.. what is the best fit to use? is it the half-cycle rectifier circuit?? (http://www.allaboutcircuits.com/vol_3/chpt_3/4.html)..

is it connected after the optional stage or before??

answer #5: i now connect the Q3b pin of the CD4518 of the timer at the hold pin of the counter so that after the timer reaches the corresponding time, the counter will hold the counting...
i add a diode so that there is no return voltage..

>>the phase lock loop circuit or IC is still not included, maybe i should finish here first, before i get to the PLL... thank you audioguru for patience...

thanks!!!!


------XOY-------

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answer at #1: you adviced me before to have a 2nd Ub1 stage, so i put it after the first Ub1 and before optional stage...

But you have only part of a filter since its R5 is missing. It will oscillate like that.

answer at #2: i use trimmers intead of resistors so i can easily adjust the frequency.

If their values aren't the same then the filter will be messed-up with a droopy response or a peak and oscillation.
If their values are less than 1k then opamps can't drive them.

answer at #3: it is already connected to the ground of the optional stage.

A Schmitt-trigger doesn't do anything with its input connected to ground. Its input needs a rectified and filtered signal.

i have tried to connect the input of the schmitt trigger to one of the LED so that only the thomping will be counted and not the thumping... (thomp-thump)

The voltage across an LED is too low to feed a Schmitt-trigger.
The voltage from the opamp that drives the LEDs is too high for a Schmitt trigger.
The output from the opamp and at one of the LEDs has a negative voltage that will damage a Schmitt-trigger.

answer at #4: i have seen so many rectifier circuit.. what is the best fit to use? is it the half-cycle rectifier circuit?? (http://www.allaboutcircuits.com/vol_3/chpt_3/4.html).

I think you need a full-wave-rectifier because you don't know the polarity of the microphone and preamp.

is it connected after the optional stage or before??

The rectifier circuit is connected before the optional stage.

answer #5: i now connect the Q3b pin of the CD4518 of the timer at the hold pin of the counter so that after the timer reaches the corresponding time, the counter will hold the counting...
i add a diode so that there is no return voltage..

The counter won't count if it is not gated on. It needs a 1 minute timer to gate it on. Then the counter needs a reset before the next counting period.

>>the phase lock loop circuit or IC is still not included, maybe i should finish here first, before i get to the PLL...

Make an ordinary 1 minute counter first before shortening its counting period.
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But you have only part of a filter since its R5 is missing. It will oscillate like that.
reply:  A.... sorry.. i now put the R5...


If their values aren't the same then the filter will be messed-up with a droopy response or a peak and oscillation.
If their values are less than 1k then opamps can't drive them.
reply: i just change the R5 and R6, and just increases it as what you have advised me (at forum#13, reply #170 at electronic stethoscope forum)..


A Schmitt-trigger doesn't do anything with its input connected to ground. Its input needs a rectified and filtered signal.
reply: i have now tried to add the fullwave rectifier, not just pretty sure about the connection and the value of its resistor...


The voltage across an LED is too low to feed a Schmitt-trigger.
The voltage from the opamp that drives the LEDs is too high for a Schmitt trigger.
The output from the opamp and at one of the LEDs has a negative voltage that will damage a Schmitt-trigger.
reply: i have added the rectifier,.. i have thought that the shcmitt trigger inverter is use to invert the negative pulse to  positive pulse... because the counter needs an input of positive voltage.. so what can you prefer to me the possibe solution..

i still have the circuit here... thanks again audio guru!!!!!!!




_______xoy___________________

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Your 2nd filter stage is correct. ;D

The bridge rectifier has an input connected to ground. Therefore it will short the 2nd filter's output when it tries to swing negative.
The bridge rectifier isn't full-wave anyway without an inverted 2nd input.
There isn't enough signal level for a passive rectifier.
The diodes should be inside the negative feedback loop of a couple of opamps that have some gain, called an Active Full-wave Rectifier.

The rectifier's output isn't filtered so will be a bunch of pulses for each heartbeat.
An Active Full-wave rectifier can have a filter capacitor built-in.

The Schmitt trigger's input is still connected to ground.
Get rid of U4 and connect the input of the Schmitt trigger to the output of the Active Full-wave Rectifier. 

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