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Old 9th April 2002, 12:41 PM   #1
PJ is offline PJ
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Join Date: Nov 2001
Location: Perth, Western Australia
Cool Designing an imaginary car CD project..

For a Commerce uni assignment we have to come up with an original product (or at least semi-original..so no "that already exists comments!! ) and come up with a business plan etc.

Its a group assignment and I, being the EE of the group have been allocated to R&D.

FWIW, im a 4th year B.com/B.EE student.

For those who care of the background, our "product" is a portable car stereo system. Basically its a discman which has a "slot" in the car stereo, so you can essentially remove the cd player from the car, leaving the "console" in which it sits in behind. The console will also consist of a radio.

By having a product which acts as a car stereo AND a discman, we hope it will appeal to students etc. Adding perhaps mp3's etc etc...either way, whether it would sell or not is beside the point, what I need your guys help for is a few starting tips

The removable cd player (discman) will contain rechargable batteries, fed off a car battery.

I need to break up the "discman" component into transport, DAC and headphone stage.

I need to break the "console" part into the preamp, radio, and power amp.

The problem is keeping the costs down. Seeing as you can get a "4x50W" head unit, which has a cdp and radio for about $AU500...building a $AU2000 car stereo setup isnt exactly going to work.

Price is more of a factor than sonic quality. I like to pay for good sound, but for this assignment...I have to go the other way

I think retail price should be around $AU600-700...so assume parts cost has to be $AU200-300, at the most. Less is better.

DISCMAN
=======

I am pretty sure I can handle the DAC section myself (using a 12V car battery source).

I am pretty sure I can handle the headphone stage myself, and their are enough projects out there for me to copy/modify one.

The problem is the transport. I cant seem to find anything either suitable for a "discman" style implementation, not anything thats even remotely close to the price range. Realistically this thing should cost about $AU50 when buying in mass quantities, otherwise the budget is going to blow out. Any ideas?

CONSOLE
=======

For the radio section I can probably buy an off-the-shelf ready to go "module". Anyone know a decent, but cheap one?

The preamp can also probably be either passive (just a pot), or somthing pretty minimalistic.

The power amp. I am sure there are some efficient IC based amps out there. Has anyone got any suggestions?


Thanks for any opinions out there. Basically I dont have to come up with a working design..just something that gives the idea that it "could be done". Its a Commerce assignment, not an engineering one

Lots of tricky looking schematics/datasheets go down well with people who have absolutely no idea what they mean..
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Old 9th April 2002, 01:22 PM   #2
PJ is offline PJ
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Default One thing I wanted to ask..

Is that most IC's I would like to use for the power amps need higher Supply voltages than 12V to obtain more than about 10W (usually less) output.

I read something about a switching supply, but its beyond my expertise, and I have never studying anything alone those lines.

Anyone know how car amps get more than about 8-9W..ie how they boost the rail voltage cheaply??
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Old 9th April 2002, 04:38 PM   #3
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As far as IC amps check this link for Nationals offerings.

http://www.national.com/parametric/0,1850,695,00.html

They have several that require significantly less than 12 V rails. You could likely use one of those. You could also use a Step-Up Switching regulator from a company such as Maxim to boost your ~12V in from the battery. These regulators are very simple to use, and maxim has lots of information on them on their website.

www.maximic.com
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Old 9th April 2002, 07:11 PM   #4
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Location: Poole, England
Default Why bother with a CD mech?

I would guess that a cd mech is going to need to be custom made for you application, what about using a laptop hard disc and making it an incar MP3 player and a portable MP3 player at the same time.

It would probably have more appeal to your target market than a cd player and (as far as i know) would also be unique (the traxdata mstation is the only commercial in car player i know of and it's not portable afterwards).

best of luck with your project
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Old 10th April 2002, 01:33 AM   #5
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As far as the MP3 player thing, if that intrests you check out www.mp3car.com. They have lots of examples. Why couldn't you use a clone of a standard car CD player transport? Maybe I'm missing something.
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Old 10th April 2002, 04:29 AM   #6
PJ is offline PJ
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Thanks for the help.

I would love to use an existing portable transport, I just cant find anything..including a price and moderate information about one..

Our "future options" include an mp3 or minidisc etc player. Using an mp3 option initially is an option...but I think CD is just as important/accessible.
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Old 16th April 2002, 11:23 AM   #7
PJ is offline PJ
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OK, I've had a bit of a look around.

I like the looks of the LM3886 Power IC. It will provide 68W @ 4ohms off +/-28V. According to the datasheet, I am going to need to get over 6A from this power source to meet this requirement.

What's the best way to get the +/-28V from a 12V battery? I find heaps of them capable of meeting the +/-28V on the maxim website, but none I see are cable of the current, and the voltage delivery required (or anything close for that matter).

Any help will be appreciated.
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