From Weekly I/O#53

How does Bluetooth work?

Video: How does Bluetooth Work?

This video does a great job explaining how our AirPods work. Some of the things I learned:

  1. Bluetooth uses different wavelengths to represent 1 and 0. It can change wavelength every 0.000001 seconds, which means it can send 1 million bits a second.
  2. Bluetooth operates in the electromagnetic spectrum between 2.4GHz and 2.4835GHz. This section of the spectrum is further broken into 79 different channels. Each channel has its specific wavelength to represent 1 and 0.
  3. Bluetooth hops around from channel to channel to send packets. For example, the phone will tell the Bluetooth earbuds to receive one packet (bits) in channel 35 and the next packet in channel 58. It hops 1600 times a second.
  4. Hopping around channels to send packets (Frequency-hopping spread spectrum or FHSS) avoids interference and eavesdropping. Therefore, multiple AirPods can play music independently and simultaneously without blocking other's wavelengths and stealing other's bits transmission.
  5. If you put your phone in the microwave (don't turn it on!), your Bluetooth earbuds will lose connection because the microwave is designed to block that signal's wavelength. Pretty useful information.

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