The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Figure 12-4. The GP1U52X infrared receiver contains a detector, amplifier,
and filter. When the receiver detects infrared energy pulsed at 40kHz, VOUT goes
low.
three connections, to +5V, ground, and VOUT. You can find this part at Radio Shack and
other sources.
Another option for MOD1 is Lite-On’s LTM-8834-2, carried by Digi-Key. It has a 32.7-kHz
center frequency, rather than 40 kilohertz, so you’ll have to adjust the oscillator, either by
adjusting R8 or by changing XTAL1. Digi-Key has a 32.56-kHz crystal that’s a good match
for this receiver.
When MOD1 detects infrared energy that is pulsed at 40 kilohertz, its VOUT is low.
Otherwise, VOUT is high. Figure 12-4 shows a block diagram of what’s inside the module.
The photodiode emits a current when it senses infrared energy in the range 880-1080
nanometers. An optical filter on the photodiode blocks visible light, to reduce responses to
ambient light. The module amplifies the detected signal and limits the peaks. A bandpass
filter centered on 40 kilohertz reduces the amplitude of signals outside of the range of 36-44
kilohertz. A demodulator filters out the 40-kHz oscillations and recreates the original pulse
pattern generated by the encoder. An integrator and comparator help to ensure a clean output
at VOUT.
The module does a good job of detecting transmitted infrared pulses at 40 kilohertz.
Unfortunately, in spite of its optical filter, it also has some response to ambient light, which
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