infrared - Arduino IR practice vs. application circuit on 1838 datasheets

There is an explanation of wiring up IR remote controllers for beginners at arduino-info.wikispaces.com/IR-RemoteControl, which suggests wiring the output pin directly into an Arduino pin. I've tried this, works fine.

The application circuits given in the datasheets for the VS1838B (Chinese) and AX-1838HS have a capacitor between VCC and GND and 10k or 20k ohm pull-up resistor between VCC and OUT.

If I understand the internal wiring diagram though, these 1838 units already have an internal pull-up resistor between VCC and OUT, so this external resistor merely changes that pull-up. Why are the capacitor and other component there? Are they filtering out noise?

Answer

The capacitor is definitely helpful for these sensors. Its absence manifests in rather devious ways, as I learned when working from a tutorial that didn’t have a capacitor: When testing the IR decoding in isolation, it might very well work. Once you add other elements to the circuit (in my case, an RGB LED), the IR decoder suddenly starts generating nonsense readings.