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#250514 - 27/02/2005 21:58 Can I get 3-8 Volts from EMPEG?
TedP member Registered: 11/01/2002 Posts: 171 Loc: South Bay, CA: USA	Hello, I just purchased a GPS receiver that I'd like to interface with my EMPEG. It can take 3-8 volts DC (~100 ma). Rather than getting an additional post-regulator, I am wondering if a low voltage is readily available within the EMPEG that I could potentially use to send over the RS232 connector and power the GPS? Cheers -Ted
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#250515 - 28/02/2005 01:01 Re: Can I get 3-8 Volts from EMPEG? [Re: TedP]
tfabris carpal tunnel Registered: 20/12/1999 Posts: 31597 Loc: Seattle, WA	I'm going to assume that you REALLY know what you're doing here... There's pics of 5 and 3 volt rails here. I don't know how much current those rails can handle. I do NOT RECOMMEND DOING THIS unless you're sure the empeg can handle it and you REALLY know what you're doing with the soldering and modding the pins on the dock and such. All sorts of things can go wrong if you try this: - Blow your empeg motherboard. - Blow something else because you grounded the 5v rail on that modded serial plug on the dock connector. - Blow something you plugged into the modded serial plug because of that 5v rail. So um, my official word on it is... don't do this. (Unofficially: This is a neat idea for powering non-12v GPSes and I wish you the best of luck in making it work.)
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#250516 - 28/02/2005 02:19 Re: Can I get 3-8 Volts from EMPEG? [Re: TedP]
genixia Carpal Tunnel Registered: 08/02/2002 Posts: 3411	Go with Tony's advice and don't do that. There is a 12V line already on the serial port. It's switched with the display. Take that, fuse it at 250mA, and use a 7808 regulator and two capacitors. You'll need to heatsink the regulator to handle 400mW. _________________________ Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.
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#250517 - 28/02/2005 03:12 Re: Can I get 3-8 Volts from EMPEG? [Re: genixia]
TedP member Registered: 11/01/2002 Posts: 171 Loc: South Bay, CA: USA	Thanks for the info. Clearly, the conservative approach is to use a DC-DC converter on the 12V line already on the RS-232 port.. especially that it's switched with the display! Any idea how much current that line is rated for? Thanks for the inputs! -Ted
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#250518 - 28/02/2005 04:09 Re: Can I get 3-8 Volts from EMPEG? [Re: TedP]
genixia Carpal Tunnel Registered: 08/02/2002 Posts: 3411	1A I believe. _________________________ Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.
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#250519 - 01/03/2005 17:01 Re: Can I get 3-8 Volts from EMPEG? [Re: genixia]
Shonky pooh-bah Registered: 12/01/2002 Posts: 2009 Loc: Brisbane, Australia	Correct. From the man himself. http://empegbbs.com/ubbthreads/showflat.php?Cat=0&Board=empeg_tech&Number=89412 _________________________ Christian #40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)
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#250520 - 15/04/2005 01:43 Re: Can I get 3-8 Volts from EMPEG? [Re: genixia]
Glen_L member Registered: 24/02/2003 Posts: 111 Loc: Elk Grove, CA	Quote: There is a 12V line already on the serial port. It's switched with the display. Take that, fuse it at 250mA, and use a 7808 regulator and two capacitors. You'll need to heatsink the regulator to handle 400mW. Bumping an old thread... I've picked up a Garmin GPS 18 LVC, which needs 5VDC. So, I'm in the same boat as the OP, but with hardly any circuit expertise. I searched Radio Shack's website for a 7808, and only came up with a 7805. Is this the right one? If I go into a B&M Rat Shack and ask for a 250mA fuse, 400mW heatsink, and pair of caps (specs?) would I be set? _________________________ No longer a stranger, finally a full-fledged member! $\:D$
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#250521 - 15/04/2005 02:05 Re: Can I get 3-8 Volts from EMPEG? [Re: Glen_L]
genixia Carpal Tunnel Registered: 08/02/2002 Posts: 3411	7805 gives 5V out, so basically, that's exactly what you need. Indeed, that's what powers my GPS interface. 100uF and 10uF. http://www.epanorama.net/circuits/psu_5v.html _________________________ Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.
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#250522 - 15/04/2005 02:07 Re: Can I get 3-8 Volts from EMPEG? [Re: genixia]
Glen_L member Registered: 24/02/2003 Posts: 111 Loc: Elk Grove, CA	Just what I needed, thanks Ian! ETA: Cool beans, I checked the GPS specs and it only pulls 60mA. So, it seems I shouldn't need the heatsink after all. Edited by Glen_L (15/04/2005 02:17) _________________________ No longer a stranger, finally a full-fledged member! $\:D$
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#250523 - 15/04/2005 02:28 Re: Can I get 3-8 Volts from EMPEG? [Re: Glen_L]
genixia Carpal Tunnel Registered: 08/02/2002 Posts: 3411	Double-check to see if that 60mA includes the antenna. Most GPS use active antennas and sometimes the current consumption for the antenna is quoted separately. _________________________ Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.
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#250524 - 15/04/2005 04:02 Re: Can I get 3-8 Volts from EMPEG? [Re: Glen_L]
Shonky pooh-bah Registered: 12/01/2002 Posts: 2009 Loc: Brisbane, Australia	Quote: Just what I needed, thanks Ian! ETA: Cool beans, I checked the GPS specs and it only pulls 60mA. So, it seems I shouldn't need the heatsink after all. Don't get too hasty there. Assuming a worst case (not really since it would be quite common) input voltage of 14V. You are dropping 9V at 60mA through a linear regulator. That is all dissipated as heat. P = V x I = 9 x 0.06 = 0.54W. Half a watt is not an insignificant amount of power. It mightn't sound like much but when it's 100% heat it is. Quote: Double-check to see if that 60mA includes the antenna. Most GPS use active antennas and sometimes the current consumption for the antenna is quoted separately. I agree. If you have an active antenna, I highly doubt that 60mA includes the antenna. _________________________ Christian #40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)
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#250525 - 15/04/2005 05:48 Re: Can I get 3-8 Volts from EMPEG? [Re: Shonky]
Glen_L member Registered: 24/02/2003 Posts: 111 Loc: Elk Grove, CA	Thanks for pointing out the snafu about the active antenna. The GPS specs seem fairly complete but make no mention as to what type of antenna is used. You've convinced me that erring on the side of caution is the best route, and I can't imagine the heatsink should be too expensive anyway. One other thing I noticed: the 5V PSU schematic also calls for a 100nF capacitor. Is that not needed in this application? _________________________ No longer a stranger, finally a full-fledged member! $\:D$
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#250526 - 15/04/2005 05:57 Re: Can I get 3-8 Volts from EMPEG? [Re: Glen_L]
Shonky pooh-bah Registered: 12/01/2002 Posts: 2009 Loc: Brisbane, Australia	Quote: Thanks for pointing out the snafu about the active antenna. The GPS specs seem fairly complete but make no mention as to what type of antenna is used. You've convinced me that erring on the side of caution is the best route, and I can't imagine the heatsink should be too expensive anyway. One other thing I noticed: the 5V PSU schematic also calls for a 100nF capacitor. Is that not needed in this application? No a heatsink won't be expensive. You can get little clip on ones for TO-220 packages, that might be enough. It certainly won't hurt. You should probably also put the 100nF (same as 0.1uF) cap in as well. The large 100uF/10uF caps provide bulk capacitance to smooth out ripple in the supply generally caused by varying loads. The 0.1uF is to filter out high frequency noise on the supply which could affect something like a GPS. It likely has this already on board, but for the cost of a 0.1uF cap (bugger all) you would be best fitting one as well - just good design practice. _________________________ Christian #40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)
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