The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Wireless Links
IREDs emit energy at specific wavelengths. Two popular types are GaAs (gallium arsenide),
at 940 nm, and GaAlAs (gallium aluminum arsenide), at 880 nm. These are both in the range
known as near infrared, to signify that their wavelengths are close to the visible spectrum.
Infrared detectors are also specific in the wavelengths they detect, although most will
respond over a range. For example, the Sharp GP1U52X receiver module is most sensitive
at 980 nm, but will also respond to the longer-wavelength emissions from GaAs and GaAlAs
IREDs. Although the GaAs IREDs are a closer match at 940 nm, the GaAlAs IREDs tend
Figure 12-8. Circuits to increase the power and transmitting distance of an
infrared link: (A) IREDs in series, (B) IREDs in parallel with PNP transistor
driver, (C) IREDs in parallel with NPN transistor driver, and (D) MOSFET driver.
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