This circuit serves to receive optical signals modulated in amplitude providing an audio signal at its output. This audio signal can be applied directly to the input of an amplifier. We can use this circuit as part of an experimental optical link in which the excitation is done by an LED modulated by a small audio amplifier. The power supply is not symmetrical and there are two components that can be changed depending on the desired performance. The feedback resistor controls the gain and can be in the range of 100 k to 4M7. The resistor R1 controls the sensitivity and can be in the range of 47 k to 1M.
