Additional circuitry is necessary to interpret the signals coming from the OPB350. One option is to connect a comparator as shown above; another option is to simply feed the results to a microprocessor. The circuit above works by comparing two voltages below the transistor to a threshold voltage, Vth. The first of these voltages is the total voltage below the transistor. The second is a certain percent of the first voltage, which can be adjusted by changing the resistor value. If both voltages are less than Vth, neither output will be high. If only the second voltage is higher than Vth, one of the outputs will be high; if both of the voltages are higher than Vth, both of the outputs will be high. These outputs can be connected to visible LEDs as status indicators or they can be connected to another circuit. This is just one possible circuit that can be used in evaluating the transistor output.