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need explanation about amplifier and filter

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Newbie level 6
Jul 9, 2007
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explanation of amplifier

hi , can anyone explain this circuit to me ? what type of amplifier it use ? and the filter and such. how to do a hand analysis of the circuit.

**broken link removed**


i find that the circuit is mostly digital... also which part of the circuit i.e.which amplifier and filter are you talking about...

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.

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.


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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