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#270830 - 28/11/2005 18:43 Suggestions for 12V -> 5V at 2.5 Amp power supply
siberia37 old hand Registered: 09/01/2002 Posts: 702 Loc: Tacoma,WA	Ok I've come up with a new hairbrained project- I want to put a Wireless AP in my car attached to the Empeg. The Empeg will be running GPSD which will allow my Pocket PC to connect wirelessly to the Empeg and use the GPSD daemon which in turn allows me to use the new Pocket PC version of Roadmap in the car with no GPS cables. My big stumbling block right now is where am I going to get the 5VDC @ 2.5 Amps that my Wireless AP needs? A 7805 regulator would seem a little too out-of-spec for this application, any other cheap ideas for this project?
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#270831 - 28/11/2005 18:53 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
tfabris carpal tunnel Registered: 20/12/1999 Posts: 31597 Loc: Seattle, WA	Lots of diodes in series? If it's good enough for car phone chargers.... _________________________ Tony Fabris
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#270832 - 28/11/2005 19:22 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
siberia37 old hand Registered: 09/01/2002 Posts: 702 Loc: Tacoma,WA	Ok duh I just found out that a 78T05 will regulate 5V at 3 Amps- and I can get them for $1.49 at BG Micro, that sounds the super easiest/cheapest route to go, unless someone with more EE experience tells me it's a bad idea that is...
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#270833 - 28/11/2005 20:11 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
Daria carpal tunnel Registered: 24/01/2002 Posts: 3937 Loc: Providence, RI	Quote: Ok I've come up with a new hairbrained project- I want to put a Wireless AP in my car attached to the Empeg. The Empeg will be running GPSD which will allow my Pocket PC to connect wirelessly to the Empeg and use the GPSD daemon which in turn allows me to use the new Pocket PC version of Roadmap in the car with no GPS cables. My big stumbling block right now is where am I going to get the 5VDC @ 2.5 Amps that my Wireless AP needs? A 7805 regulator would seem a little too out-of-spec for this application, any other cheap ideas for this project? I had that idea, incidentally, and never finished it. Since then I've actually started selling off bits I had for it.
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#270834 - 28/11/2005 20:11 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
Daria carpal tunnel Registered: 24/01/2002 Posts: 3937 Loc: Providence, RI	Quote: Ok duh I just found out that a 78T05 will regulate 5V at 3 Amps- and I can get them for $1.49 at BG Micro, that sounds the super easiest/cheapest route to go, unless someone with more EE experience tells me it's a bad idea that is... Heat dissipation?
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#270835 - 28/11/2005 20:52 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
matthew_k pooh-bah Registered: 12/02/2002 Posts: 2298 Loc: Berkeley, California	Have you considered a bluetooth GPS? They're actually built to eliminate just the wires you're trying to eliminate. It'll also save you serious battery power over wifi. Matthew
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#270836 - 28/11/2005 21:12 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: matthew_k]
siberia37 old hand Registered: 09/01/2002 Posts: 702 Loc: Tacoma,WA	Quote: Have you considered a bluetooth GPS? They're actually built to eliminate just the wires you're trying to eliminate. It'll also save you serious battery power over wifi. I have- but I would like to still use the GPS in the empeg sometimes- might come in handy when I forget or don't have the pocket pc. Good point about the power consumption though- I guess I can forget running the music on the Accessory setting anymore, would probably drain my battery to fast.
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#270837 - 28/11/2005 21:36 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: siberia37]
matthew_k pooh-bah Registered: 12/02/2002 Posts: 2298 Loc: Berkeley, California	I'd advise you to check into the various comercial mapping programs. Does roadmap do routing yet? I've got a Mobilecrossing Waypoint, and it's at the same time really easy to use and nearly impossible to use while driving. RoadMap on the empeg at least is a great hack, but it's not really usable. As to the car battery, I suspect it'd power the WAP for a while without a problem, someone else can probably do the math for you. Matthew
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#270838 - 29/11/2005 09:29 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: Daria]
Shonky pooh-bah Registered: 12/01/2002 Posts: 2009 Loc: Brisbane, Australia	Quote: Quote: Ok duh I just found out that a 78T05 will regulate 5V at 3 Amps- and I can get them for $1.49 at BG Micro, that sounds the super easiest/cheapest route to go, unless someone with more EE experience tells me it's a bad idea that is... Heat dissipation? I concur (as an electrical engineer). Using a linear reg like a 7805 will mean at 2.5A on a 13.8V supply you'll need to dissipate (13.8 - 5) * 2.5 = 22W. That is completely impractical to dissipate. That's a metric sh*tload of heat. A switching regulator like a LM2575 or otherwise should be considered. These need extra external components to run though. I'd look for something pre-made since I'm not sure you have the skills. I'm sure you can get some sort cigarette lighter to 5V adapter capable of that current. It would have the switching regulator all set up to go. _________________________ Christian #40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)
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#270839 - 29/11/2005 14:28 Re: Suggestions for 12V -> 5V at 2.5 Amp power supply [Re: matthew_k]
siberia37 old hand Registered: 09/01/2002 Posts: 702 Loc: Tacoma,WA	Quote: I'd advise you to check into the various comercial mapping programs. Does roadmap do routing yet? I've got a Mobilecrossing Waypoint, and it's at the same time really easy to use and nearly impossible to use while driving. RoadMap on the empeg at least is a great hack, but it's not really usable. As to the car battery, I suspect it'd power the WAP for a while without a problem, someone else can probably do the math for you. Don't know any commercial mapping programs that would support using GpsD as a GPS data source, so that would require me getting a bluetooth gps and giving up using any GPS applications on the empeg. Roadmap doesn't support routing yet and probably never will support on-the-fly point-to-point routing because of the one-way and intersection information that is missing in the TIGER map data it uses (some are working on other map sources though). That said, I've had it in my mind to add GPSApp's routing paradigm into Roadmap (i.e. use Google maps to create the route, then display your pre-created route with directions), so maybe this would be a good catalyst for that.
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