38 Khz Sensors

erco

I find it interesting that the general frequency of 38-40 kHz is preferred standard for many sensors

1) IR communication & control
2) ultrasonic distance sensors, such as PING))) , and
3) underwater locator beacons (per https://en.wikipedia.org/wiki/Underwater_locator_beacon)

Is it some sort of magic number/golden ratio/divine proportion for general wave propagation of different energy forms through different mediums?

I was probably at my physical fitness peak at ages 38-40. Little did I suspect...

abecedarian

A hold over from remote control TV "clickers" that operated in ultrasonic frequencies, so even though IR is technically a higher frequency, the modulation was kept the same to make the transition from ultrasonic to IR TRX easier to implement... or at least that's what I've been told.

xanadu

The Number 38, starring Jim Carey.

Heater.

No idea really but I will hazard a guess:

Go lower than that and we get into audio frequencies which would be very annoying.

Go higher than that and we get into radio frequency bands. We used to have broadcast radio down at 100KHz.

Then I think abecedarian has a point. Like many things in electronics and computers tradition carries us along.

erco

Heater. wrote: »

Then I think abecedarian has a point. Like many things in electronics and computers tradition carries us along.

Could also be availability of cheap 455 kHz IF resonators. From https://en.wikipedia.org/wiki/Consumer_IR

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.