42 votes
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Why 2.4 GHz Band?

2.4 GHz is one of the industrial, scientific and medical (ISM) radio bands. ISM bands are unlicensed, which makes it easier to certify the equipment with FCC (or its counterparts in other countries). ...
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  • 35.9k
42 votes

Does Bluetooth interfere with WiFi?

Yes, WiFi and Bluetooth can disturb each other. But both are equipped to handle that. A standard that is not capable to handle disturbance and/or interference will simply be unusable under many ...
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  • 78.8k
27 votes

Why 2.4 GHz Band?

The "special" thing about 2.4GHz is that when spectrum was allocated for various needs in the 60's and 70's, no one wanted it, because it was thought that atmospheric water absorption made it useless....
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  • 6,650
21 votes

Does Bluetooth interfere with WiFi?

Wifi uses a listen before transmit system. If the channel is busy, it holds off transmitting. Eventually it gets through. Each channel is fixed. If it tries to use a channel that is busy, from ...
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  • 70.7k
15 votes
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What will I see in oscilloscope when attempting to analyze Bluetooth or Wi-Fi signals?

If it's a good scope, you'll see nothing at all, just a flat line representing DC.. Ironically if it's an inferior scope with incompetently designed input amplifiers and the signal strength is high ...
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  • 65.8k
14 votes

Why 2.4 GHz Band?

It is 'special' since it does not go very far. Strangely, this turns out to be an important advantage as many devices and people can use the same band in near by area without interference. Tele ...
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  • 979
14 votes
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Should the unused areas on the top layer of my RF PCB have ground pours?

RF Engineering is "Pure Black Magic." Proponents will insist it is not, but unless you have a PhD in physics, it probably will seem so. The concepts of resistance, capacitance, and inductance, which ...
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  • 11.8k
12 votes

Bluetooth dual mode (BR/EDR + LE)

Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) is typically used for relatively short-range, continuous wireless connection such as streaming audio to headsets. Bluetooth low energy (LE) is ...
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  • 46.9k
11 votes

BLE Scan interval and window

There is another aspect to this that is being missed in the other answers. As per the Core BLE specification, only one advertising channel is being looked at during each scanInterval and is rotated ...
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  • 111
10 votes
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Possible to re-program microcontroller over Bluetooth?

Yes, you can do remote firmware updates with the STM32. Now you have two choices: using the STM32's factory-programmed bootloader writing your own bootloader Using the factory-programmed bootloader ...
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  • 1,362
10 votes
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What is the minimum distance that BLE 4.0 capable device be programmed for..?

The goal of this rather long analysis is to ensure you look like the sharpest RF dude your company has ever hired :) The free space path loss range of a an RF system can be calculated. For a typical ...
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  • 1,810
10 votes

Why is the latency so high for Bluetooth audio?

This is just an approximation to what is happening: - Streaming bluetooth packet size is about 1 kByte. If you are sending MP3 music at 192 kbits per second that's about 24 kB per second so 1 kB ...
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  • 378k
9 votes
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Is Bluetooth less susceptible to jamming than wifi?

Bluetooth operates in the 2.4 GHz band using 79 channels, spaced 1 MHz apart, from 2402 MHz up to 2480 MHz. Bluetooth is less susceptible to jamming than Wi-Fi since Bluetooth uses a technology ...
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9 votes
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Bluetooth versus WiFi

Bluetooth and wifi serve very different purposes. Bluetooth is designed for connecting peripherals to computers at short range (<10M) and moderate data rates. It aims to minimize power consumption....
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9 votes
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Why are contacts missing on some of these M.2 modules?

The contacts are missing because they're not used. The A-key variant of the m.2 spec has provisions for display port signals while the E-key variant drops the display port and adds SDIO, UART and PCM (...
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  • 3,569
9 votes
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How deep underwater can Bluetooth reliably transmit?

The question has been studied extensively. According to this lecture, at 2.4GHz (microwave frequency as well) the 1/e (63% loss) occurs in 1.4cm. You probably can do better with 9600 baud UART. :-(
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9 votes
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void loop executes even when the while loop inside is true in arduino

Serial communication is transmitting data one byte at a time. Your code is fast enough to read and process one byte before the next one is received. There are many possible solutions to this, and ...
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9 votes

How do true wireless earbuds perform inter-ear communication?

I can't stand not knowing how this works so I did some research by reading some patents - their language is intentionally vague in some areas, but I did discover some commonalities in what they ...
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  • 249
8 votes
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2.4GHz antenna feed routed through pcb via?

There are many similar questions here, such as Should there be more clearance on RF vias with microstrip?, and Calculating Signal Loss (dB) Through Vias, and How to minimize characteristic impedance ...
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  • 11.8k
8 votes

How can I make Bluetooth (2.4 GHz) reception area narrow and controllable?

Neither will work. If you build a metal case with a narrow opening, you'll have an even wider beam; the smaller the aperture, the larger the beam. It's practically impossible in this form factor to ...
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7 votes
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Must FCC-certified modules be labelled with the correct FCC ID?

Here's my understanding. Since it is a radio module, then it is definitely an intentional radiator and if they claim it has been FCC-certified it should have an FCC ID on each module. You should ...
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  • 46.9k
7 votes
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How to configure HCI UART for 3 Mbps?

HCI/SPP refer to the communication protocol. They both use a standard UART, just at different baud rates. However, the SPP mode and HCI mode are very different. HCI mode bypasses a large part of ...
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7 votes
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How much does the physical size and shape of a RF antenna affect its range/penetration?

How much does the physical size and shape of a RF antenna affect its range/penetration? Completely. Utterly. An antenna is fully defined by its shape and size and material. A minor modification in ...
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7 votes
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Bluetooth: chip or module?

Let's start with the bottom line: What is the total price difference between the IC solution and the module solution (Taking only the CC2541 vs. the RN42)? This turns the question into a balance ...
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  • 17.6k
7 votes

What this NPN transistor circuit do?

The only reference to "MFB" in the CSR64215 datasheet is the VREGENABLE signal on pin 40. In the datasheet there's a pushbutton switch to connecting VREGENABLE to Vbat. The circuit you show is ...
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  • 78.8k
6 votes

HC-05 Bluetooth module not responding to certain commands

The answer is in the HC-05 documentation: you have to make sure the Key34 is connected to Vcc when sending some AT Commands. simply hold your button down while pressing ENTER in your terminal. http:...
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6 votes

Does the orientation of a Bluetooth antenna affect the transmission distance?

Edit: I was wrong, it can. Here's a picture of a similar antenna: And here's it's radiation pattern: The radiation pattern is a polar plot of the relative gain of the antenna at each angle. As Andy ...
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  • 1,648
6 votes
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Does the orientation of a Bluetooth antenna affect the transmission distance?

Yes it does, in contrary to other answers. It's not an isotropic antenna and will have more gain in one direction than another. This affects transmission distance. Using the example shown in ...
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  • 378k
6 votes
Accepted

Wireless EEG electrode design

You can't transmit the voltage of an electrode, because that does not exist: a voltage is always between two points, so you need at least two electrodes connected to your transmitter. In practice you ...
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