The infrared diode is not biased. When no infrared signal come on it, the voltage at the input of the filter is 5V. When infrared signal come on it, the voltage at the input of the filter is -5V. When the infrared signal oscillates, because the data transmission is an oscillating signal (up to...
The batteries are used to convert the infrared signal into electric signal. Of course, the electric signal is alternative. The filter lets pass only the good frequency. But it has other ways to do that. We can use only the voltage source of the computer's power supply. We have to use the red...