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TomTom Voice instruction though traffic alerts?

 
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NigelC
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Joined: Nov 17, 2003
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PostPosted: Tue Nov 25, 2003 4:11 pm    Post subject: TomTom Voice instruction though traffic alerts? Reply with quote

Hi
Is there a device that can take the earphone output from the PDA and broadcast it locally so that the voice instructions are played through the car radio as traffic alerts?
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lbendlin
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PostPosted: Tue Nov 25, 2003 8:03 pm    Post subject: Reply with quote

Check out the in car FM modulators, for example here http://shop.store.yahoo.com/csexpo/fmmodulator.html
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Davidb67
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Location: Newcastle upon Tyne, U.K

PostPosted: Tue Nov 25, 2003 10:29 pm    Post subject: Reply with quote

Nigel, I think you're asking a question I was wondering last week:

Have the TomTom Navigator Voice Instructions come through car audio, but ONLY as an interruption to whatever you're listening to at the time - i.e. tape/radio/cd, in much the same way as traffic announcements on RDS, no??

I'm wondering if all these audio modulator type devices just pick up a "constant" feed - eg MP3/wav, or sat/nav, since I think they require you to "tune" into an FM frequency. that means you're effectively constantly listening to the "radio".....

I'm not sure if I'm wrong on this, as I've never tried one of those modulator-type devices.

Just my 2-penneth worth!
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lbendlin
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PostPosted: Tue Nov 25, 2003 11:18 pm    Post subject: Reply with quote

If that's what you really want then you are pretty much at the mercy of the wiring in your car - it may or may not expose the "MUTE" connector for the car stereo where you normally connect the car phone in. I know that all of the newer Blaupunkt radios have that connector. As said before, originally this was to allow the car phone to go over the car radio speakers, and to mute any music when the call comes in or you initiate one. Putting the headset output of the PDA onto that produces the same result.
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ErnieS
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PostPosted: Sun Jan 25, 2004 5:53 am    Post subject: Reply with quote

To get what you are after you would need to mimic the way radio stations do it ie. Commercial radio stations broadcast three tones or 'bleeps' before and after the travel bulletin, The tones allow RDS radios to recognise the presence of the bulletin, and switch over to the radio accordingly. For the TA feature to work, the function marked TA, TI, TP or 'Traffic' must be switched on.
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DavidW
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PostPosted: Sun Jan 25, 2004 11:59 am    Post subject: Reply with quote

FM modulators are illegal in the UK if they radiate in free space (as all the ones I've seen for sale recently do). They fall into the category of unlicensed radio transmitters.


The traffic announcement feature isn't as simple as "three tones or bleeps" - RDS uses a fairly low speed digital carrier (1187.5 bits per second) superimposed on an FM radio signal that is beyond the audible range. An earlier system for traffic announcements simply used a pilot tone beyond audible range to indicate a traffic bulletin; I don't believe this system is used any more, as it has been made obsolete by RDS. It was certainly used in Germany.

An FM signal contains the Left plus Right signal at baseband; if your radio is only mono, everything else is removed by the filters - of course, Left plus Right is mono. Higher up (at 19kHz; FM radio has an upper audio frequency of around 16kHz) is the stereo pilot tone; if a stereo receiver finds that, it knows it's tuned to a stereo transmission.

The difference signal (Left minus Right) is a stereo transmission is on a 38kHz subcarrier. The classic way to separate the channels is to add the two signals for the left channel and subtract the difference signal from the baseband signal for the right channel.

RDS is on a 57kHz subcarrier (deliberately chosen to be 3*19kHz).



David
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ErnieS
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PostPosted: Sun Jan 25, 2004 3:21 pm    Post subject: Reply with quote

Sorry David, Yes you are correct in what you say I was trying to keep it simple and not get too technical whilst putting the idea across in fact I just cut paste it from the IBA guide to RDS... It's quite a while since I played with broadcast radio... Now ask me how the encryption works on a Digital Tetra Radio System and we are cooking with gas.... Laughing Out Loud,
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DavidW
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PostPosted: Mon Jan 26, 2004 11:53 pm    Post subject: Reply with quote

No problem - all I was attempting to say really is that there's no easy way to fake up an FM signal that includes TP flags - as it's not as easy as simply generating tones. EON (the ability to switch from a national signal to a regional station for a traffic bulletin) is more complicated still.

Many of the RDS encoders used on broadcast signals are pretty basic - particularly those used by local stations. If you have a radio capable of displaying the text, you'll find that it tends to be just one or two repeated phrases on most stations (certainly that's the case around here for both commercial and BBC local stations).

On the other hand, DAB stations tend to have something useful in their textual output (called DLS on DAB; I forget what the correct term is on RDS FM - possibly RadioText).



David
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bardel
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PostPosted: Mon Jun 14, 2004 7:08 pm    Post subject: Reply with quote

lbendlin wrote:
If that's what you really want then you are pretty much at the mercy of the wiring in your car - it may or may not expose the "MUTE" connector for the car stereo where you normally connect the car phone in. I know that all of the newer Blaupunkt radios have that connector. As said before, originally this was to allow the car phone to go over the car radio speakers, and to mute any music when the call comes in or you initiate one. Putting the headset output of the PDA onto that produces the same result.


This sounds ideal to me, no messing with FM transmitters and allows me to listen to my music and have the SatNav interupt when it needs to, just like a proper in car satnav system would then???

Most aftermarket car stereo's have telephone mute wiring nowadays I think... I'm off to find my car stereo's manual to check the wiring diagram out, if it all looks positive then I might not need the Arkon powered dash mounting thingy when making my first venture into ppc's next week!!! Smile

If anyone's done this or got any tips, I'd like to hear them.

Cheers

Barry
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icsys
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PostPosted: Mon Jun 14, 2004 8:30 pm    Post subject: Reply with quote

Hmmm.... this sounds interesting.
I've no idea how you would get it to work but if it does then I may try this idea too Thumbs Up
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DavidW
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PostPosted: Tue Jun 15, 2004 12:54 am    Post subject: Reply with quote

I've mused on this before. The big problem with using the phone input is that most stereos are too slow to switch - I know my Vauxhall OEM system is too slow (you'd have lost most of the voice command by the time the stereo switched over to the phone input). If the phone input is already in use for a phone car kit (as mine is), it makes the circuitry more complicated, and devising a mute signal from a Pocket PC will require some circuitry.

Some stereos have an input for navigation systems - obviously if you have one of those, use it!


I had wondered whether the QuBiT products offered a solution to this - my ideal would be to 'steal' one speaker (the front right) from the stereo for the PDA audio and optionally assert the mute line as well (in this case, it doesn't matter if it swings in half a second after the PDA has started talking).

I was intending to find out about this - but unfortunately the idea landed on my all too long "to do" list and stayed there.



David
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bardel
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PostPosted: Tue Jun 15, 2004 11:14 am    Post subject: Reply with quote

OK, I've had a look at my Pioneer Car Stereo manual for the wiring inputs for telephone muting / signal, and it would seem that there is one wire (yellow/black) going into the ISO connector marked Audio Mute Lead and there is also a seperate connector labelled "TEL Terminal" which says refer to handsfree telephone unit's manual (sold seperately).

Im presuming a signal needs to be passed to the yellow/black to perform the audio mute. Any ideas on what this needs to be (+5V ?)

Lastly, Im guessing the TEL terminal is something along the lines of a 3.5mm jack for the audio feed? Can anyone confirm this?

Cheers

Barry
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bardel
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PostPosted: Tue Jun 15, 2004 11:28 am    Post subject: Reply with quote

Just looked at an online manual for Alpine stereo's and they have an "audio interupt" (which I assume does the same as muting) which requires a ground connection to mute the audio.
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DavidW
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PostPosted: Sun Jun 20, 2004 2:14 pm    Post subject: Reply with quote

Ground to mute (or, if the stereo has a phone input, to switch to the phone input) is the nearest thing to a standard. Certainly that's what Nokia car kits are designed assuming - they have a very weak pull-up on the mute pin in the wiring loom, which is pulled low when the car kit wants to mute the stereo.

An "active low" signal means that several devices can use the same input "open collector" style.


The problem about the time taken to switch over remains, though.



David
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