This stage is intended to receive modulated optical signals, using as a receiver a photodiode. Photodiodes equivalent to the original may be used, with preference being given to types that are fast enough to respond to the transmitted signal. The signal may have its characteristics adapted to the 680 k ohm resistor value change. In fact, this resistor can assume values between 470k ohm and 1M ohm. This circuit can be used as a shield for microcontrollers.
