41

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). However, what special about 2.4 GHz? There is about a dozen ISM bands. Some at higher frequency, others have lower frequency. Not all ISM bands are ...


38

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 circumstances. The 2.5 GHz ISM band is also used by Microwave ovens and other wireless standards like Zigbee. Wifi transceivers are able to detect when certain ...


27

Yeah, it's entirely possible. I commented on this previously and have since looked into it further. You can have the triggering Bluetooth device send the activation signal through its friendly name. The friendly name is the human-readable name that appears in the the list when you search for a Bluetooth device to pair with. The speed at which this ...


26

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.


24

I don't mean to rain on your wireless parade. You've ran into a tough but unexpected requirement. Something like that warrants re-evaluation of the whole system design. 1st thing that comes to mind is to clock both units off one oscillator. You have Bluetooth communication, which hints that the range is on the order of 10m. You could connect your units ...


19

Nothing. That is, you'll just see a flat line, as if there's no signal. It's too high frequency to see. The input stage on a 50 MHz scope is not configured to pass a 2.4 GHz signal. It'll be filtered out, and you'll be left looking at the (probably nonexistent) low-frequency components of the signal.


17

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 bluetooth, then it will wait. This may reduce the data speed for wifi if it has to wait too much. Bluetooth for over a decade now uses adaptive frequency hopping (...


15

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 enough, you may see a step in the flat line when the poorly filtered RF carrier is demodulated by nonlinearities in the amplifier, but that will only tell you ...


14

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 density is the term used in phone industry as how many cordless phone per square mile. Early generations (25 years ago) coreless phone use few MHz and tens of MHz ...


14

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 makes sense at DC and low-frequency (up to some MHz), are completely skewed when it comes to high-frequency design and implementation. Traces can behave more ...


13

I have also been playing around with BLE, and decided to go with the Nordic nRF8001 chip because it looked easier to work with and didn’t require expensive IAR tools. nRF8001 is slightly cheaper than the CC2540 part in BLE112, but it is slave-only. I bought Nordic’s nRF8001 development kit for $99, which includes nRF8001 samples and several nRF8001 boards (...


13

The amount of data which you can transmit is generally determined more by the bandwidth which you are allocated than by the actual frequencies of the band. However, allocations at higher frequencies tend to be larger than allocations at lower ones. An allocation up in the GHz range might be 50 MHz wide; while the comparably sized range from 50-100 MHz is ...


12

The short answer is yes, it is possible to use Bluetooth without pairing. However, it is still going to always be a point-to-point link. There are also potential issues with not using pairing (mainly the lack of security and the lack of good support for this mode of operation). Whether it can be done depends on your receiver's Bluetooth hardware. I'm ...


12

BLE is very unsuitable for even medium bandwidth streaming (audio or video), because it is designed for transfer of few and small data packets with lots of sleeping time in between. This is why it is called 'low energy' and not 'low power' - it reduces the amount of picojoules per bit for small packets with respect to competing standards. Other standards ...


11

To put it simply, it doesn't do the same thing as older Bluetooth chips. The new chip uses BLE, or Bluetooth Low Energy. This is a mode which transmits packets at a high bandwidth in very short bursts, enabling the exchange of data with a very low duty cycle. When transmitting or receiving, power consumption is comparable with standard Bluetooth, but the ...


11

This idea might be patented, so it might not be suitable for a commercial project, but you can actually measure the position and orientation of one electronic device relative to another, with reasonable accuracy, using magnetic fields. This is how Polhemus and Ascension trackers work. They are used in VR motion tracking, and in surgery for tracking the ...


11

Yes, you will get more signal strength from a 7 dBI antenna than a 2.2dBI (specifically 4.8 dB). It solves that by radiating energy more directionally than an idea antenna that radiates evenly in all directions (0 dBI). This increased signal strength of 4.8 dB is 10^(4.8/10) = 3 times more power. That will increase your range by about 70% in ideal ...


11

You can think of antennas similar to your vision. 0dB would be considered you just as you with nothing artificial. Now you decide that you would like to use a pair of binoculars to see further. The problem with binoculars is that your viewing range is not as large as you have with out them. However, binoculars are helpful, they let you see things that you ...


10

This can be accomplished with a technology within the Bluetooth brand called Bluetooth Smart (or Bluetooth Low Energy / Bluetooth 4.0) And also depending on the phone you have. The main benefit with Low Energy over regular Bluetooth is that it consumes a lot less power, and the expected lifetime of a device could be years depending on the connection ...


10

GPS modules with 1pps outputs are readily available and inexpensive. It isn't really necessary to discipline the CPU's oscillator to the GPS (e.g., with a PLL). As long as you can "timestamp" external events relative to the CPU clock, it's relatively straightforward to interpolate the time of your wave transmit and receive events between any two PPS events. ...


10

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 to the next of 3 channels with each interval. So if there is RF interference on that channel you might not see the device even if you have the scanWindow equal ...


10

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 class 2 Bluetooth system, assuming +4dBm of transmit power, -70dBm receiver, & unity gain antennas, you will find that the range that gives you 74 dB of ...


9

Bluetooth is a half-duplex radio technology that has a peak raw data rate of 1, 2 or 3 Mbps, depending on the specific modulation scheme being used. In practice, an application can get at most about 200 KB/s of data throughput. Even if you reduce your video requirements to quarter-VGA (320 × 240) at 10 fps with 8 bits/pixel (768 KB/s), you'll still ...


9

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 called Frequency-Hopping Spread Spectrum (FHSS). This means the signal "hops" from one channel to another, using a pseudorandom sequence known to both transmitter ...


9

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 (aka I2S), I'd bet those are the ones missing, especially as this is a dual use card (as it has both the A and E key slots present, any pins that differ between ...


9

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 using delays is not a good one. You could send a marker character at the end of each command, e.g. LED_ON!. Then you know you have to keep adding characters to ...


8

Unfortunately in my experience what you'll quickly find is that video is obnoxiously difficult to manipulate without a lot of cpu power. Let's start from the beginning: how much video do you want? There are a lot of choices here, but start small. Let's say that, for simplicities sake, you wanted a 640x480 frame of 8-bit black and white video, at 24 frames ...


8

I have implemented a wireless clock synchronization for microcontrollers before, but only with millisecond accuracy, which was good enough for the application. From my reading, this paper explains microsecond synchronization quite well: http://www.math.u-szeged.hu/tagok/mmaroti/okt/2010t/ftsp.pdf Essentially, if you have knowledge of the transmission event ...


8

The basic organization of Eagle files is that all libraries used end up in the final .brd and .sch file. There exists a User Language Program (ULP) that can export all the parts contained in a schematic, including the package footprint called exp-project-lbr.ulp. This file should be included with your Eagle installation. (thanks to this YouTube video for ...


8

Well, with 100kbps, you may be able to stream a low quality video the size of a post stamp :-) Without any precision, I will imagine you want HD (not even full HD) @30fps in H264, with average motion (factor 2), an approximate bitrate estimation could be : (1280px*720px)*30fps*2*0.07 ~= 3800kbps So you have to reduce this by a factor 38 (at least !). Say ...


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