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PMB-648 GPS Module satellite lock? — Parallax Forums

PMB-648 GPS Module satellite lock?

sdinardosdinardo Posts: 3
edited 2013-08-24 15:44 in Accessories
Purchased one fr Radio Shack. Can I power it at 5V by batteries just to see if I can get a Satellite lock? When connected to my controller (R-pi, modelB), I only get a flashing LED, never a lock. It is positioned with clear view of sky. When conncected to R-pi, I had red to 5V, blk to Gnd, and yelow (Tx) to pin 10 (Rx).

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-08-24 08:06
    You should be able to power the PMB-648 from batteries. You have to make sure the voltage is in the range of 3.3V to 5V which means 3 Alkaline cells in series or one LiPo cell. It shouldn't make any difference whether the PMB-648 is connected to the R-pi or something else. Try not connecting the yellow lead, so there's only power going to the PMB-648. It should lock. If not, there's a problem with the power coming from the R-pi. If it locks when the yellow lead is not connected, but won't lock when it's connected to Rx on the R-pi, then there's a problem with the Rx input on the R-pi. Maybe it's not an input. Maybe it's an output and it's shorting out the lead from the PMB-648.
  • sdinardosdinardo Posts: 3
    edited 2013-08-24 13:15
    Mike Green wrote: »
    You should be able to power the PMB-648 from batteries. You have to make sure the voltage is in the range of 3.3V to 5V which means 3 Alkaline cells in series or one LiPo cell. It shouldn't make any difference whether the PMB-648 is connected to the R-pi or something else. Try not connecting the yellow lead, so there's only power going to the PMB-648. It should lock. If not, there's a problem with the power coming from the R-pi. If it locks when the yellow lead is not connected, but won't lock when it's connected to Rx on the R-pi, then there's a problem with the Rx input on the R-pi. Maybe it's not an input. Maybe it's an output and it's shorting out the lead from the PMB-648.

    Thanks, Mike. I used a 9vbattery + a voltage regulator (7805), to be sure would deliver enough voltage (in case the pi was not), and still had some trouble getting a satellite lock. BUT, it turns out there was/is some interference from either my pi or my monitor blocking a good satellite lock. With the battery hooked up and disconnected from the pi (i.e., away from the pi), I got a good lock. So, once I moved the GPS 1 meter away from the pi / monitor, I could get a lock with the GPS connected to the pi (5v and Gnd). This all took a bunch of troubleshooting to confirm. Now, using only the yellow (Tx) to the pi's Rx GPIO, everything is working. I will figure out later whether indeed it is the pi or my monitor that is interfering. If it is the pi, that is a little concerning long-range, because this is supposed to be all in a balloon payload eventually. Just FYI, on the pi I I just have a USB keyboard, HDMI/VGA to a screen, and the pi's input power adapter; it is not running anything else (yet).

    Anyway, thanks.
  • Mike GreenMike Green Posts: 23,101
    edited 2013-08-24 15:19
    Most people don't appreciate how noisy something like a R-pi can be. It's often not in a shielded box and some of the cables coming off it may not be shielded (like the power adapter). The standard system clock speed is about 700MHz with the 2nd harmonic not far off from the frequencies used by GPS. You really have to figure on using some kind of shielding around the R-pi. Conductive paint will do or glued-on aluminum foil. Just make sure the coating is contiguous and connected to the power supply ground.
  • sdinardosdinardo Posts: 3
    edited 2013-08-24 15:44
    Helpful, Mike. Much appreciated.
    /S
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