I've done quite a few IR apps with Vishay IR modules, and I've never needed any additional
pull-ups for anything less than 40kHz carrier freq.
The internal pull-up built into the IR module has always been sufficient, BUT, you can
improve pusle-forming with a stronger external pull-up for high-speed applications.
Doesn't really apply to your app, but just FYI.
Our Fyre-Fly high-speed IR transceiver module used an external pull-up of ~2.2K for
improved pulse-forming at higher data rates.
Some of the lower frequency IR modules may be influenced by ambient light sources, so
you may want to look into better shielding. Red filters help, and recessing the IR module
back into an enclosure to help block ambient lighting helps too, but you want a very stable
and clean DC power supply as well to reduce false triggering. Shoot for <20mV peak-to-
peak noise or hash on your power supply rails for solid operation.
A few more tips;
Modulate your carrier as close as possible to the center band-pass frequency of your IR
module for best range.
Use an IR LED with a wave-length as close as possible to the peak spectral sensitivity
region of your IR module.
Block as much ambient light as possible with filters.
Make sure to locate your IR module as far as possible from your PIC, oscillator, and use a
star configuration for power. A star power route is just separate traces directly from your
regulator + output to each IC.
Then make your lower layer a solid copper pour, connected to ground, and route each
ground connection from each IC directly to the ground plane with a short trace to a via.
If you do add an external pull-up, make sure it doesn't exceed the current capacity of your
IR module when active.
Bookmarks