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we are designing a fairly compact PCB for a communications device. We are looking at using BLE as a link for voice to a separate microphone, and BT Classic to be paired with a smartphone. We are using pre-certified modules, and they will located on the PCB about 20mm away from each other (can extend this to 40mm if need be). Is there a risk of interference between the 2? We are transmitting audio in both cases so interference would be particularly noticeably. They both operate at 2.4GHz, but I understand they have different frequency hopping techniques, and hoping this will allow for coexistence.

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  • \$\begingroup\$ BLE has rather low data rates, and is thus a poor choice for voice data. I strongly suggest looking at BT classic or other wireless protocol(s). \$\endgroup\$
    – Turbo J
    Commented Aug 24, 2018 at 10:27
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    \$\begingroup\$ the absolute maximum throughput of BLE 4 is 12kbps (punchthrough.com/blog/posts/…), which is pretty awful for audio (youtube.com/watch?v=53tdYmJuUmM) \$\endgroup\$
    – BeB00
    Commented Aug 24, 2018 at 15:16
  • \$\begingroup\$ Actually BLE is capable of 2Mbps. \$\endgroup\$
    – T. Chains
    Commented Aug 24, 2018 at 18:59
  • \$\begingroup\$ only ble 5, not ble 4. \$\endgroup\$
    – BeB00
    Commented Aug 25, 2018 at 4:43
  • \$\begingroup\$ BLE 5 could probably transmit audio, but the bigger issue is a lack of support from the Bluetooth organization. They would have to standardize the protocol for it to be useful on an iPhone or Android phone. So far it seems like they don't have any intention of doing that. You didn't explain any details about what the device was interfacing with. If it were talking to an OS, you'd be out of luck without Bluetooth Classic to provide the audio profile. If you had your own hub, you might be able to roll your own protocol with BLE. \$\endgroup\$
    – getonup
    Commented Aug 7, 2020 at 16:57

2 Answers 2

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They do not interfere with each other for most use cases. I've used them together in two different projects. I never had any issues.

Other people have pointed out that BLE might not be right for your application. I would definitely agree with them. With that aside though, for your more general question, yes you can definitely use them at the same time without worrying too much about interference.

When you use Classic and BLE at the same time, they complement each other. Typically, a product would use BLE for control. This results in the occasional transmission of small amounts of data. If a product integrated Classic as well, it would use Classic to transmit large amounts of data at a higher throughput. The device would see-saw back and forth between the two stacks. In that situation, they wouldn't interfere with each other. If you tried to transmit large amounts of data through both channels at the same time, that might result in poor performance for more reasons than just a shared frequency spectrum. They would also share the same antenna and processor.

Both stacks use some shared resources to keep the links alive, but Bluetooth doesn't require much to maintain connections by design.

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They are both 2.4GHz, but BLE uses an adaptive frequency (channel) hopping algorithm to avoid congested parts of the the spectrum, so at least BLE should tolerate Classic. Not sure about the other way around. Presumably it should be fine because BLE will avoid Classic to the benefit of both.

As for audio, it's all digitized by the time you are in Bluetooth, so you won't get degradation in quality, but maybe dropouts.

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