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Old 9th March 2004, 08:12 AM   #1
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Location: Australia
Default Car HU Discussion

I've seen a few people interested in the car audio side of digital so i thought it deserved a thread of its own, plus I'm going to start building one in the not too distant future.

My plan sofare is to use an 18f pic (exact model i'm unsure off, something with alot of i/o's for a start), writting the program in CSS's Pic C compiler which if you ever have a look has great inbuilt functions to make life easier. CD audio will come from a CD-rom drive and controlled over ATAPI but the audio over the digital out to a DIR1703 for simplicity.
For processing the signal, the TAS3103 can provide Volume, EQ, time alignment (or so alpine call it) and spectral analysis. It can also do a host of other cool features but as yet i don't have the knowlage to implement them.
All of this leading to a 24 bit DAC, with info on a lcd of some description (graphic maybe, money permitting)
The only thing to stop this being comparible in features to a high end car audio head unit is the radio. Sofare ST and phillips offer chipsets to output FM/AM but all are complex to implement.
ST have the ST 7580 for IF decoding and TDA7515 as the frontend.
BUT... there is extremely limited info on the TDA7515 in the data sheet, so no I2C commands or example circuit.

Phillips do a range of NICE (New in car entertainment) radios which, as far as i can tell, are IF stages
However , the TEA6825, looks alot more promising.
In the datasheet there is a full schematic to get audio(!) using itself and the TEA6811.

Anyone of the solutions would be nice but i don't know what controls the selection of channel frequency. ..
Can anyone surgest a solution or any comments on my plan sofare?
(also can someone explain the antenna-> IF -> audio thing, I've just assumed from what i've seen on datasheets)

Many Thanks
Matt
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Old 9th March 2004, 12:39 PM   #2
MWP is offline MWP  Australia
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Join Date: Oct 2002
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Are you sure using a CDROM drive is a good idea?
Itll be pretty much useless when driving... itll skip constantly.
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Old 10th March 2004, 07:20 AM   #3
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A CD rom is the only thing available...
Other than surrounding it in foam to lessen the vibrations there no other solution to it.
a HDD and a mp3 decoder would be better but it would take alot more work.
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Old 10th March 2004, 11:16 AM   #4
MWP is offline MWP  Australia
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Join Date: Oct 2002
Location: Adelaide, South Australia
Quote:
Originally posted by fr0st
A CD rom is the only thing available...
Other than surrounding it in foam to lessen the vibrations there no other solution to it.
a HDD and a mp3 decoder would be better but it would take alot more work.
Actually i think it would be easier doing HDD+MP3 than CDROM and worrying about dampning.
There are plenty of HDD+MP3 schematics around the place, so it wouldnt be difficult to build.
Plus, no swapping CDs
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Old 11th March 2004, 07:42 AM   #5
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Join Date: Dec 2002
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MWP, I think i remember playing you on iinet's UT2004 server.... small world

I have some DS89c450 uC's coming from maxim/dallas for the project. I managed to find a small program that hex dumps sectors from the hdd onto the serial port of a 8051 which looks promising as a basis for the project.
I'd have to implement my own fat32/16 interpreter since sofar noone has released thier code for it.

MWP - Have you ever seen somewhere in aus that carries the STA013 (or any hardware mp3 decoder chip ), RS and Farnell are both out, altronics are jaycar don't stock parts that exotic
Furlec seems to be the only place that have graphic lcd's aswell (>$200)
I'll keep looking
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