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?


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.

  • \$\begingroup\$ Alright, I'm running LED strips too, so I'll pick up the capacitor, thanks! As Andy said, the 47 uF capacitor and 47 ohm resistor do this, so presumably I need both. Any need for the extra pull-up resistor? \$\endgroup\$ May 7 '13 at 1:12
  • \$\begingroup\$ Also, the VS1383 sheet shows two capacitors, but capacitors symbol I've never seen before. It's vaguely remenicent of a polarized capacitor, so I'm wondering if that second capacitor deals with AC related noise in the system? \$\endgroup\$ May 7 '13 at 1:40
  • \$\begingroup\$ @JeffBurdges The capacitor symbol for the 100uF capacitor is a standard electrolytic capacitor symbol, while the one marked 104 indicates any generic non-polarized 100 nF capacitor. There is no "ac related" factor in this (all noise has an AC element)! The arrangement is a typical decoupling and noise filtering solution for supply to noise sensitive components: The "why two caps" question has been asked and answered often on this site, please do read about it. Using the caps for an IR receiver is highly recommended. \$\endgroup\$ May 8 '13 at 2:14
  • \$\begingroup\$ Cool I found answers : electronics.stackexchange.com/a/60946/12189 electronics.stackexchange.com/questions/59325/… \$\endgroup\$ May 8 '13 at 17:13
  • \$\begingroup\$ Any idea how close the capacitors should be to the IR sensor? \$\endgroup\$ Jun 7 '13 at 20:09

I think you refer to this diagram: -

enter image description here

The external pull-up is greater than 10k (note the ">" sign) - this means don't use anything equal to or less than than 10k - an open circuit is of course no problem.

The capacitor and 47 ohm resistor are there to improve noise immunity from the power supply. They probably aren't needed but the supplier is recommending them as a precaution

  • \$\begingroup\$ Any clue how noise might appear from the user's perspective? Wrong button reads? It's presumably not something you could fix in software like denouncing a button. \$\endgroup\$ May 6 '13 at 11:38
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    \$\begingroup\$ There is a high gain amplifier in there, so a low noise supply makes sense. If you're happy stabbing at buttons on the remote three times in the hope that it'll eventually work, you probably don't need the extra components! \$\endgroup\$ May 6 '13 at 11:39
  • \$\begingroup\$ @MichelKejizers your edit was not only unecessary, it made things far worse - "equal to or less than (or equal to)" ???? \$\endgroup\$ Dec 28 '18 at 23:21
  • \$\begingroup\$ @Michaelk, why did you see it necessary to edit this answer? \$\endgroup\$
    – Andy aka
    Dec 29 '18 at 0:18

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