Author Topic: The Connecting/pairing challenge — part 2  (Read 1109 times)

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The Connecting/pairing challenge — part 2
« on: 2013-12-03 13:01:56 »
What to watch out for As we discussed in “Bluetooth on the motorbike”

There are a number of pitfalls you might fall into when setting up your system.

Often as not, when referring to Bluetooth modules—I’m referring to units which are incorporated into another manufacturer's product.  Most of the end products (that is the stuff that you end up buying off the shelf or the net, as the case may be) consists of components from a number of different manufacturers. Very few brand name producers, for instance, make their own transmitters or receivers. They shop around for smaller or larger bits of their designs, based on spec's and cost, and incorporate them into their own products. Such is all manufacturing today. It poses the added problem of good integration and interaction between the different components inside a product not only between products. The end result and the amount of problems it'll carry with it, boils down to good design and engineering, but at the same time it poses an extra challenge to you whenever you are trying to mix and match product for your total set up.
KC5290_H50 height=50

A refresher:
1) Any Bluetooth module can only connect/pair to another Bluetooth module with the same profile
2) Any Bluetooth module can only connect/pair to one other module at a time.
3) Any Bluetooth module is either a transmitter or a receiver. (Some modules are able to change mode as needed, but it is only the one or the other at any given time.)

Compounding the problem of the smaller "built in" Bluetooth modules is that they do not have an easily available user interface, like a screen or a keyboard. That means that you are often left in the dark as to exactly what is happening when you are trying to set them up.

Normally they are fitted with a button that is pushed to start the pairing process, and often, a blue and a red light to indicate the process.
When discussing the pairing process, I mentioned a four digit code that one keyed in on both units in order to confirm the connection to be made, as when pairing a cell phone to a headset. So what happens with two modules that does not have the ability to let you confirm key-codes (simply because they lack input possibilities)? If you're in luck they resort to the same standard code (which often is 0000),but sometimes, they don't. If the one module uses 0000 and the other, say 1234, your luck just ran out: You cannot make the two modules pair up and connect.

To avoid this stalemate situation, some manufacturers have built in the capability to acknowledge many or all 4 digit codes. When receiving a request for pairing the unit will first try the obvious ones (like 0000 or, if that doesn’t work; 1234 and so on) until it is accepted or the process times out (normally after 1-2 minutes).

But, unfortunately, not all units handle this. Which is often the reason you will not be able to connect two modules from different manufacturers.

Another, common reason connecting/pairing problems, are modifications made by manufacturers to applied protocols or profiles.

What this means is, that even when two modules allegedly use the HSP profile—some manufactures modified the application of the profile on their module and in the process altered the way the module communicate with other modules. Their intentions are often the best (like wanting to improve sonic quality),but the loss of some communication facilities an unseen consequence. The result is that you may end up with two modules using the same profile and security code (the 4-digits),but still being unable to communicate.

A point in case: KC Wirefree (,a major manufacturer of Bluetooth modules and software, has put this on their website:

Custom kcAudio Profile
Our patent pending kcAudio profile is a real time Stereo + Intercom Entertainment System. There are two major
features in the kcAudio profile that do not exist in standard Bluetooth A2DP.
First, we use a fast, real time encoding compression algorithm. With this low latency algorithm, we deliver wireless
stereo audio from start to finish in less than 45ms, which is 300‐400% faster than standard Bluetooth.
Second, we added a high quality live intercom back channel, which is far superior to standard Bluetooth Headset Profile
(for cell phones). The Headset will send a microphone signal wirelessly, back to the Audio Adapter.
The high quality microphone channel is excellent for demanding speech recognition or voice command usage.

As we have discussed elsewhere, the A2DP profile can only send a stereo sound in one direction. Like from a mp3 player to a stereo headset.
But with the kcAudio, provided that both transmitter and receiver are using modules from KC Wirefree – they will at the same time also be able to send a microphone signal in the opposite direction.

That would be a perfect solution for all motorbike headsets.

But alas—this will only work when and if all Bluetooth modules used for a motorbike intercom are using modules from the same manufacturer.
It's the same story for many manufacturers; they amend or modify the profile or the way the sound is transmitted.

Here often lies the root of the problems in connecting/pairing modules from different manufacturers, or even between different versions (software and/or firmware) from the one and same producer.   
« Last Edit: 2013-12-03 14:24:39 by STeinar »
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