This circuit is suggested by Motorola, making it possible to use an optical coupler of type 4N26 together with an amplifier of type MC1741 (741), with a gain of -10 times. The AC signal applied to the emitter (LED) must have a peak amplitude of 5 mA, serving to modulate the beam of light, which then appears as an equivalent signal at the output of the operational amplifier. Note that, despite the existence of a 10mA bias current in the emitter, only the AC component appears at the operational output.
