It's interesting to note that 38-40 kHz is the preferred frequency for standard ultrasonic sensors, underwater acoustic beacons, and IR control. Black box flight recorders ping at 37.5 kHz: https://en.wikipedia.org/wiki/Underwater_locator_beacon
That's 3 very different mediums, sound through air, sound through water, and light. Coincidence, magic, or the golden ratio of frequency/wavelengths?
Related, older IR remote protocols, incl Sony SIRC, used 40 kHz. That has changed to 38 kHz universally now. Gooder? Mo bettuh? Why?
Carrier frequency: Usually fixed carrier frequency, typically somewhere between 33 and 40 kHz or 50 to 60 kHz. The most commonly used protocol is the NEC protocol, which specifies a carrier frequency of 38 kHz. The NEC protocol is used by the vast majority of Japanese-manufactured consumer electronics. The Philips RC-5 and RC-6 protocols both specify a carrier frequency of 36 kHz. However, the early RC-5 encoding chips divided the master frequency of the 4-bit microcontroller by 12. This required a ceramic resonator of 432 kHz to achieve a 36 kHz carrier, which was not widely available. Many companies therefore used a 455 kHz ceramic resonator, which is commonplace due to that frequency being used in the intermediate frequency stages of AM broadcasting radios, resulting in a carrier frequency of 37.92 kHz (essentially 38 kHz). Even documentation for Philips' own controller chips recommended an easier-to-obtain 429 kHz ceramic resonator, yielding a carrier frequency of 35.75 kHz. Modern IR transmitters typically use 8-bit microcontrollers with a 4 MHz master clock frequency, allowing a nearly arbitrary selection of the carrier frequency.
Comments
https://www.parallax.com/sites/default/files/downloads/28015-PING-Detect-Distance.pdf
Note that the above links to a MS Word document, not a PDF. (Why?)
Walter
https://www.parallax.com/downloads/ping-ultrasonic-distance-sensor-product-guide
The other is a chapter excerpt from a Smart Sensors text.
That's 3 very different mediums, sound through air, sound through water, and light. Coincidence, magic, or the golden ratio of frequency/wavelengths?
Related, older IR remote protocols, incl Sony SIRC, used 40 kHz. That has changed to 38 kHz universally now. Gooder? Mo bettuh? Why?
Carrier frequency: Usually fixed carrier frequency, typically somewhere between 33 and 40 kHz or 50 to 60 kHz. The most commonly used protocol is the NEC protocol, which specifies a carrier frequency of 38 kHz. The NEC protocol is used by the vast majority of Japanese-manufactured consumer electronics. The Philips RC-5 and RC-6 protocols both specify a carrier frequency of 36 kHz. However, the early RC-5 encoding chips divided the master frequency of the 4-bit microcontroller by 12. This required a ceramic resonator of 432 kHz to achieve a 36 kHz carrier, which was not widely available. Many companies therefore used a 455 kHz ceramic resonator, which is commonplace due to that frequency being used in the intermediate frequency stages of AM broadcasting radios, resulting in a carrier frequency of 37.92 kHz (essentially 38 kHz). Even documentation for Philips' own controller chips recommended an easier-to-obtain 429 kHz ceramic resonator, yielding a carrier frequency of 35.75 kHz. Modern IR transmitters typically use 8-bit microcontrollers with a 4 MHz master clock frequency, allowing a nearly arbitrary selection of the carrier frequency.
To skew even further OT, this reminds me of the story about how horse butt sizes defined rocket engine specs.