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p0nta
Joined: 09 Jul 2007
Posts: 12
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 09 Sep 2007 7:11 Ads |
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A.Anand Srinivasan
Joined: 15 Oct 2005
Posts: 1792
Helped: 216
Location: India
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09 Sep 2007 11:31 Re: need explanation about amplifier and filter |
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| i find that the circuit is mostly digital... also which part of the circuit i.e.which amplifier and filter are you talking about...
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Eugen_E
Joined: 29 Nov 2004
Posts: 358
Helped: 31
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09 Sep 2007 12:09 Re: need explanation about amplifier and filter |
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The analog circuit around LM358 has 2 stages:
- a non-inverting amplifier, with A=((R13 + R12)/R1 +1), that uses the first opamp of LM358 (INA+, INA-, OUTA);
- a comparator with the second opamp (INB+, INB-, OUTB).
At OUTA the voltage is variable, so D7 will give a variable light in the heartbeat rythm. The comparator transforms the variable voltage in a square signal, so D5 will light at maximal intensity or will be off in the heartbeat rythm.
R14 sets the trigger level for the comparator and since the heartbeat voltage variation at OUTA can be in any range between 0...5V (depending on the finger opacity, thickness,...) R14 should be set for adequate triggering.
A Schmitt trigger, or positive feedback to introduce a little histeresis would be better, to avoid false detection.
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p0nta
Joined: 09 Jul 2007
Posts: 12
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09 Sep 2007 15:29 Re: need explanation about amplifier and filter |
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Thanks , nice explanation.
hurmm... but how about the C7, R2 , R10. what is the function of it? also for C5. if i would like to test the circuit by applying a generator which point should i put it to ? at the ORP12 or at R8 ?
oh and maybe the explanation for the digital part would be nice also. beginner.
thanks.
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p0nta
Joined: 09 Jul 2007
Posts: 12
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11 Sep 2007 6:53 Re: need explanation about amplifier and filter |
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i ve done the circuit. this is the results. how come i get like a wrong results at pin 7.
i tot it should be like this.
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