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GPS invallid data when serial port is connected — Parallax Forums

GPS invallid data when serial port is connected

cereal2ndcereal2nd Posts: 11
edited 2010-10-23 09:20 in Accessories
hey,

i'm trying to get the "PMB-688 GPS SiRF Internal / External Antenna" gps module to work.

it has a led that shows a status of the gps information if its valid or not.

So when i only have the power connected the led turns on after a minut, so it has vallid data.

Now when i connect the serial port, the led keeps flashing even after 30 minuts, so no valid data.

any ideas?

Comments

  • FranklinFranklin Posts: 4,747
    edited 2010-10-22 10:23
    What do you connect the serial port to? Is the device in the same location in both cases? Are all other factors the same?
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-22 10:24
    i'm connecting the serial port to a foxboard (TTL serial port)

    And yeah the device is at the exact same location ....

    another problem is that i don't recceive a thing on the serial port ...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-22 16:27
    What are you using for its +5V (power)? Maybe that's hosing your deal?

    GPS's Data_out is the yellow wire. The LED stays up once it's acquired its sats. I get great reception with the unit sitting on a benchtop in the house - without using the external antenna.
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-23 04:19
    5v is a power supply that can deliver 5v @ 2 A so thats not the problem

    and yeah i'm using the yellow wire as rx data
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-23 07:01
    I don't know what a 'foxboard' is; you'll have to talk that up.

    What's its comms requirement? Is it "TTL"?
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-23 07:46
    foxboard => http://foxlx.acmesystems.it/

    i have the gps chip directly connected to the serial port /dev/ttyS2
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-23 08:01
    I brought mine back out.
    It blinks while it's acquiring. Cold-starting, it took about 40secs to do that and then it stays on solid.

    Maybe you have a bad unit, but it's more likely it's the interconnect. Everybody has to be on the same GND/V_ss.

    PE - I'd be in there with a scope, seeing what's going on, but that's me.
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-23 08:31
    yeah, i'll try to bring a scope from work next week to see whats wrong.

    But the wierd thing:

    if i connect the unit to the foxboard no data is received
    if i connect it to a usb to ttl convertor i get the output nicely ...

    thats onaother wierd part


    about vcc/gnd

    its battery powered so everything is on the same power source
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-23 08:46
    If you're sure that the foxboard is TTL (5v); because if the foxboard is RS232 then it won't work, you'll need a converter between the two. The 688 output is Parallax "True" at 4800 8N1.
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-23 09:05
    hmm,

    the foxboard defines:
    All the logical levels are 3,3V (5 volt tolerant)

    so i gues si don't need a voltage convertor
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-23 09:10
    I guess you're good there.
    Get that scope (or bring the beast in to work with you.)

    -- You can always try some metering, too. --
  • cereal2ndcereal2nd Posts: 11
    edited 2010-10-23 09:12
    PJ wrote:
    -- You can always try some metering, too. --

    what do you mean with that?
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-23 09:20
    Voltmeter, DMM, etc.

    For instance, I know my data is good on my terminal, but I can also measure 2.4 - 2.8V (varying) on the Data_out pin showing that data is active.
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