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I have made a circuit but I fail to interface optocoupler with preamplifier can any one help to troubleshoot,when I disconnect preamplifier the output from the AC Voltmeter is 0.5 Volts but when I Connect preamplifier to the optocoupler the output voltage is 0 volts.enter image description here

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  • \$\begingroup\$ What is the input? What is the output? Where is the preamp? What result do you expect? Component values and part numbers are unreadable if supplied at all. \$\endgroup\$
    – jippie
    Commented Mar 1, 2014 at 11:04
  • \$\begingroup\$ Input is square waveform with a duty cycle of 8% and frequency of 10kHz the output is square wave form with amplitude of 0.5volts,the preamplifier part is portion of the circuit from ph phototransistor to the opamp output terminal,my expectation is to obtain the wave form that corresponding to decaying and growing curve like cahrging and discharging of capacitor. \$\endgroup\$ Commented Mar 1, 2014 at 11:34

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Remove the led connected in parallel with the optocoupler (unless it serves a purpose there) and connect the cathode of the opto-diode to the ground.

schematic

simulate this circuit – Schematic created using CircuitLab

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