Author Topic: Bluetooth on the motorbike  (Read 1239 times)

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Bluetooth on the motorbike
« on: 2013-12-03 13:03:21 »

A shot at a non-technical explanation of the Bluetooth® technology.

Bluetooth®  is the name of a wireless technology standard for connecting devices. Wireless, obviously, means that it is intended to relieve you of the hassle of using cables. It uses radio signals in the 2.45 GHz frequency range to transmit information over short distances. By embedding a Bluetooth® chip and a receiver in products, signal carrying cables may be eliminated.
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To illustrate: An iPod wired to a Bluetooth box (a transmitter)—the transmitter transfers the sound to another Bluetooth box (a receiver) which then transfers the sound by cable to the helmet speakers.

The Bluetooth boxes could have any shape and mounting.  Some devices have the transmitter built into the design—like a Bluetooth enabled GPS or a dongle to a mp3 player. The receiver could be a unit mounted in or on the helmet, or perhaps a small box for your pocket.

One should note that a transmitter can only communicate with a single, dedicated receiver at a time, just like the receiver only can pick up signals from one transmitter. This is a crucial point in Bluetooth communications; and one that creates a whole lot of confusion and frustrations. I will get back to that in a moment.

First, I think it necessary to lay out and explain some of the terms used in connection with this technology.
HSP ( :   (Headset Profile)

This is the most commonly used profile, providing support for the popular Bluetooth headsets to be used with mobile phones, etc. The HSP is able to simultaneously transmit and receive a (mono) sound.

A2DP ( :  (Advanced Audio Distribution Profile)

This profile defines how high quality audio (stereo or mono) can be streamed from one unit to another.

A Bluetooth unit is able to use only one profile at a time.
Hence, a Bluetooth device using a HSP profile cannot communicate with a unit that is using an A2DP profile.
(It is possible to automatically switch profiles, but more on that later.)
So, in reference to the illustration above—the likely assumption is that one is applying the A2DP profile. That gives you stereo sound to your helmet.

Now, take a look at the following setup:
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Some units have more than one input connector, and may also have more than one output connector.

But—in this case—the audio (coming from the iPod and the GPS) is mixed into one stream going out, which is sent to the receiver unit.

The receiver is then capable of receiving sound from both the iPod and the GPS—and pass this on to two helmets.

Both helmets will be fed the same signal and hear the same music /GPS sound (or from whatever source may be hooked up to the transmitter).

And, importantly, there are no communications transfers between the two helmets.

Let's take a look at a more complicated helmet "box":
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Since one Bluetooth unit only can communicate with one other, dedicated unit at a time, and with only one profile—we will explore the use of an advanced "helmets box".

Sound from all 4 units are here mixed into a single sound stream to the helmet. In addition, the sound from the helmet microphone is distributed to two Bluetooth units.

We can connect /pair one HSP module with an iPod, and another with the GPS. The sound is only going from the iPod/GPS to the helmet, and not in the other direction.

One A2DP module is connected with the cellphone, and the last A2DP module to the other helmet—which is fitted with the same kind of unit.
 Remember: An A2DP profile can send mono sound in both directions simultaneously.

This enables the main helmet carrier to listen to the iPod, the GPS-guiding and have a phone call going on the cell phone—all at the same time.

The transmitter, as we have mentioned, can only communicate with one receiver at the same time; so what happens to the pillion rider helmet? He/she will only hear what the rider is saying into his microphone.

The pillion rider could connect/pair with his/her own iPod (or cell phone, etc.),but not to the one that the rider is connected to.

Probably not what we wanted — was it ?

The pillion rider would also want to listen to the same sources :-)
And even more complicated—the A2DP unit in the rider's "box" has to be in transmit mode—and the other in receive mode.
 (The terms are not the technically correct ones, but let's use them for now.)

There are some commonly used work arounds to handle this, but most of them are functionally flawed, and—surprise—quite expensive. An example:
Few people would want to have music fed to their ears while trying to execute a phone call on their cell. So the trade off we could make, is to make the Bluetooth module a little smarter by setting priorities between the optional sources, and to listen to these sources in a round-robin sort of way.
Say that we put the cell phone at the top of the priority list (# 1),GPS is #2 and sound from the iPod #3.

By programming the Bluetooth module we make it listen to all three sources in sequence (at a rate of many times a second). If it finds that one of the modules is sending something to "me" it will make a connection with that device/source.
I will be listening to music on priority #3.  The unit scans the two other units and looks for connection requests.
 In comes a phone call. As the cell phone has higher priority (#1) than the music, the module temporary disconnects the music streaming from the iPod, and puts through the Bluetooth module in the cellphone.

But wait! You have to switch profiles as well (from A2DP to HSP—it's nice to be able to both listen and talk on the phone…)

Ok, now you are in a cell phone conversation, and effectively shut out from the music (which is nice),but also from any warnings/messages from the GPS (which is not nice). And the poor pillion rider cannot listen to the phone call, because that conversation is being hogged by your HSP! And suppose you had something set to an even higher priority than the cell phone (#0),what would happen if this signal was directed to the pillion rider? Well, you could still have your call, but only as long as the pillion rider is not saying anything; the instant he/she starts talking you will be blocked from hearing anything of your own phone call.

One should also consider that this switching of channel and profile — takes time: sometimes milliseconds, sometimes a second or two. So most of the systems handles this by putting two modules in the helmet "box"—one smart unit that can connect/pair to more than one "channel"—and one module with a HSP profile—which is in constant connection to the pillion rider.
By this time you should be getting the general idea - Bluetooth is simple matter for a multipurpose system like a motorbike intercom.
But, there is such a thing as a near-perfect system for a motorbike Smile
Take a look at this:
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The helmets each have one Bluetooth module for permanent communication between helmets, and one "multi-channel" module with priority and protocol switching.

The cell phone connects to the GPS and the GPS to the rider's helmet. The pillion rider will not hear the GPS or the cellphone connected to the GPS.

The "Audio Platform" has two Bluetooth modules that are transmitting using the stereo HSP profile — one module to each helmet.

This "Audio Platform" has multiple inputs — and all inputs combine into one sound stream. FM radio, MP3 player and a USB stick holding MP3 sound tracks.

The rider and pillion rider are talking to each other on constant "channel"; the rider can listen to the GPS, cell phone and music devices through the "Audio Platform"

The pillion rider can talk with the rider, and listen to the same music source as the rider. The pillion rider can also connect to (pair with) his/her own cell phone — or even his/her own Bluetooth enabled MP3 player.
What about Bike2Bike communication ?

Well, some systems (helmet sets) are able to connect to other helmet sets, enabling you to converse with this other rider as if it is your pillion rider.

However, Bluetooth has a very limited range, and the signal is easily blocked if something comes between transmitter and receiver.

Typically, the range is exhausted at 200-300 meters for the high power versions, and as low as 20 meters for the low power versions.

Which makes it less than very useful for all practical purposes.

Fortunately, there are systems that also can cope with those shortcomings—take a look in the menu for further descriptions!
« Last Edit: 2013-12-03 14:30:10 by STeinar »
** Wired and Bluetooth intercom from **