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Thread: GPS receiver with external antenna?

  1. #41
    Maximum Bitrate bes51659's Avatar
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    Answers from Trimble

    I have got answers from Trimble about questions I've had. I thought that I'll share the answers in case someone else wants to build a GPS receiver. Cut from email conversation, but if you are really interested I think you will understand it anyway :-)

    I got the answers thanks to courtecy of Richard Desfosse, Regional Manager Of Southern England, Diamond Point International (Europe)


    **************************

    Q1) Pin 14 is the reference voltage for the A/D converter, which converts the gyro output signal. It's always connected to the gyro supply voltage.
    Q2) The Lassen DR-manual shows the suitable gyro rating for the given application circuit. It's actually not the input spec on the GPS-module itself. Lassen-DR "learns" the actual gyro characteristic and is continuously self-calibrating. But the x5 amplifier is needed for 2,5 mV/degree/s gyros in order to bring the signal into the optimal dynamic range.
    Q3) The circuit of Trimble’s Starterkit board has several load options for different gyros with different supply voltages. NO_LOAD resistors are footprints on the PCB that are not populated with a resistor. They're open by default and 0-Ohm resistors could be assembled for different gyro versions.
    Q4 Trimble say maybe you are right but, as long as the circuit works (which it does), it doesn’t matter.

    Regards,
    Mark Gurney
    Technical Support - Diamond Point International (Europe) Ltd


    1) Pin 14 is for the internal gyro circuitry – for your gyro it is 3.3V.
    Q1) Just to be 100% sure: So I connect this pin to my 3V3 regulator? Not the 3.0V one that is supplying the gyro itself?
    8) See last attachment. (schematics)
    Q2) Since gyro is specified 2,5mV / degree / s and input of GPS is the same. I do not understand the x5 amplification on your adapter board. That gives 12,5mV from the gyro, doesn’t it?
    Q3) What is NO_LOAD resistor? I use Epson XV8100. Should I put an actual resistor into my design?
    Q4) Seems to me the filters on the diff amp stage is not symetric on vref and vout intput. And impedance is not balanced either. Am I wrong? Are maybe noise and output impedance of vref and vout not symetrical?

    Thanks, BR, B-O Swing


    2) Yes. Pin 1 has a square solder pin. Top row will be odd, bottom row will be even.
    3) Leave floating
    4) Pin 14 is for the internal gyro circuitry – for your gyro it is 3.3V.
    5) Yes
    6) Ask Epson – its their part
    7) Trimble 5V antennas have a voltage range of 5V +/- 0.5V. So 5V should be fine
    8) See last attachment.

    Mark


    1) Can I leave pin 1 unconnected? (I think so) (btw. I have not found how the contact is numbered! Can you tell me how you’ve numbered it?)
    2) Can I leave pin 11 unconnected? Reset input should probably be pulled-up or grounded.
    3) What is pin 14?Input gyro voltage??? I guess it is just to connect it to 3,3V
    4) Is direction high = reverse?
    5) Epson gyro is 3.0V +-0,15V. My regulator is at 3V3. I guess I need a germanium or schottky diode maybe to lower voltage-But since the Epson XV-8100 is on list of supported devices I am just a bit suspicious that a spec might be wrong. Please confirm.
    6) feed of 5,5V to active antenna. But input voltage is specified as 5V... Is there a buck boost or something internally on the module?
    7) I need a better version of the schematics in order to see filter component values etc.

    BR, B-O Swing

    Attachments:

    dev kit schematics (high resolution)
    App Note 1
    App Note 2

  2. #42
    Maximum Bitrate bes51659's Avatar
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    [media]http://web.comhem.se/mulle2/pcb_delivery.jpg[/media]

  3. #43
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    bes51659 -> Looks really great man, pleas let us be updated :-) Cause thinking of building the same device myself :-)

  4. #44
    Maximum Bitrate bes51659's Avatar
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    Some progress. I am waiting for 2 components and is forced to a 2week pause right now.

    [media]http://web.comhem.se/mulle1/progress.jpg[/media]

    [media]http://web.comhem.se/mulle1/progress2.jpg[/media]

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    Just thought I'd chime in. Looking good!

  6. #46
    Maximum Bitrate bes51659's Avatar
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    Thanks guys! I will probably be able to sell this piece of kit eventually. Depends on interest.

    Today I got my first NMEA log! Wonderful feeling... (below)

    It will take a bit longer to try out the gyro circuitry. I also want to write the code for interpreting BMW IBus speed messages and simulate tacho pulses before I am done with this design. So with an E46 you will not have to connect tacho and direction signals. You can do if you've got another car.

    Plan is to be done in June.

    [media]http://web.comhem.se/mulle2/GpsWithAntenna.jpg[/media]
    BMW OEM GPS Antenna (part numbers are visible)

    [media]http://web.comhem.se/mulle2/gpsfront.jpg[/media]
    GPS in box.

    Edit:
    I've now got valid GPS data so I know that my antenna is working!¨

    $GPVTG,000.0,T,,M,000.0,N,000.0,K,A*0D
    $GPRMC,132321.93,A,5921.39125,N,01758.66222,E,000. 0,000.0,230408,,,A*53
    $GPGSA,A,3,27,08,04,07,02,25,,,,,,,5.05,3.47,3.68* 04
    $GPGSV,3,1,12,27,40,188,39,10,14,300,,13,85,142,,0 2,40,277,32*78
    $GPGSV,3,2,12,20,11,133,,29,12,348,,23,,000,,08,10 ,198,34*70
    $GPGSV,3,3,12,16,25,060,,04,37,230,41,25,61,154,32 ,07,43,178,40*73
    $GPGGA,132322.93,5921.39122,N,01758.66224,E,1,06,3 .47,00024.4,M,023.4,M,,*6F

    Btw. Is someone using time data to set time in car?

  7. #47
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  8. #48
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    Look's sweet, will be interestet... But what do you think the price will be? And what kind of technology is the GPS using, how many channels and so?

  9. #49
    Maximum Bitrate bes51659's Avatar
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    It is sweet isn't it :-)

    It is the top of the line module from trimble. I think that is its edge, lots of satellites and dead reckoning. And you can use the OEM GPS antenna.

    And it will contain power functionality. That is it will power on PC and LCD with configurable timing as well as rearview camera, remote input on poweramp, etc. On a BMW with IBus you will get extra nice features.

    My two prototypes was 358€ (each!), but I will be able to shave some of off that. Box alone was 70€ which is what you normally pay for the entire gps receiver :-)

    When I've verified design and completed code I will put it into "General Hardware - User innovations" forum with youtube links.

  10. #50
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    [media]http://web.comhem.se/mulle1/progress_3.jpg[/media]

    Proto 1 fully assembled and I think I've found all design errors. Next week I will make my first tour with it in my car. Writing code for the 8051 at the moment!

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