The input impedance of the detector is around 300kO, which doesn’t appreciably load the source. The diode is operated with a slight forward bias so a regular silicon signal diode (e.g., 1N914) can be ...

Figure 1 shows a very simple microcontroller-based circuit that can alternately emit and detect light using just two I/O pins on the microcontroller and an LED and resistor.

A simple Zener-diode stabilization network circuit using D2 supplies a voltage of 100 V dc. The value of R1 depends on the source voltage and must be calculated with the equation, R1 = (V ac −s ...