PMB-648 not sure if it's defective

I purchased a PMB-648 off of Amazon the other day because it was cheap and did NMEA. The claim on Amazon and on the packaging is that I can change the baud rate. I've scoured the internet for the past three days. I've tried Sirfdemo, gpsinfo, direct connection via FTDI. No matter what commands I send it with and without checksum the GPS doesn't acknowledge anything has been sent. I've seen some posts that it when they sent invalid commands they would get an error. I'm using the ttyl connection. I'm debating on trying the RS232 connection to see if that would help me. From what i read online it goes to the same serial connection so it seems pointless. Also does anybody know what the TP1 pad does?

I need the baud rate to be at least 9600 for my drone project.

Thanks for any help


  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    Did you say you were sending commands without the checksum? I don't believe it will respond if it doesn't get a complete message. I vaguely recall using the Sirfdemo to change the baud rate before on the 648 / 688.
  • I've tried with and without. When I try to change to sirf binary the software changes to 38400, but I don't get any output in the screen. If I go back to 4800 it's still outputting nmea
  • Talking to the PMB-648 via the logic channel takes some doing. You'll need to add some circuitry, which I describe here:

    Also, I've attached some Spin code that illustrates how I communicated via SiRF to configure the unit. Maybe it will help.

  • I'm using an arduino to talk to the gps. what exactly does the spin code do? I've never read spin code before. If I use RS232 I shouldn't have a problem? What kind of transistor do I need to make this circuit? I'm more of a programmer than a circuit guy. Also is it true that this GPS won't save it's settings and that I need to configure it every time I turn it on?

    Thanks for the information! Going to attempt to talk to this via RS232 instead till i figure out how to build the ttl circuit
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,541
    edited 2016-05-10 - 01:32:37
    RS232 should work without additional circuitry, assuming you have an RS232 interface to begin with.

    The transistor is just a jelly-bean PNP: 2N3906, 2N2907, etc.
    Also is it true that this GPS won't save it's settings and that I need to configure it every time I turn it on?
    That's been my experience.

  • I'm readding the sirf demo manual and was wondering what the target software for the pmv-648 is under the target s/w menu?
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