GPS Module

HW-595 Board

uBlox GPS Board

• Based on uBlox NEO-6M-0-001
• Receiver Description
• 5V operation (3.3 V regulator onboard)
• UART: 4800 - 230400 bps (9600 bps 8N1 default), TTL levels buffered by 220R resistors
• U.FL connector supplies 3.3 V to active antenna
• Crystal Osc, not TCXO
• PPS LED: Invertion of PPS pin
• Battery-backed RAM contains config data and clock and speeds first-time-to-fix
• Data in NMEA 0183 format
• More background here

Board pinouts:

Pin	Function	Description
1	PPS	1 pulse/s, synchronised at rising edge, length 100 ms (by default)
2	RXD	UART input
3	TXD	UART output
4	GND	Ground
5	VCC	3.3 - 5 V

PPS:

• Send PPS to UART via CTS to allow GPSD to acurately sync
• Can be configured as a frequency reference: 0.25 Hz - 10 MHz
  • Output has high frequency accuracy
  • Suffers from jitter except at a few specific frequencies
• Configure in u-Center here
• Different frquencies/duty cycles can be configure for GPS synced/not synced

Software

U-Center

• U-Center
• Select COM port and Baud rate
• Communicates with uBlox with binary UBX Protocol

To view/change settings: View -> Configuration View; to activate change: Send

• PRT (Ports)
  • Baud Rate : 9600 -> 115200
• TP5 (Timepulse 5)
  • PPS Settings for no GPS lock (eg use as an "alert" signal:
    • Frequency : 1 Hz -> 10 Hz
    • Duty Cycle : 100% -> 25% (alternatively set to 0% for permanent low output)
  • PPS Settings for GPS Locked:
    • Frequency Locked : 1 Hz
    • Duty Locked : 50%
  • Rising Edge on TOS
  • Cable Delay : 50 ns -> 10 ns (This compensates for cable delay between antenna and receiver)
  • UBX -> CFG (Config) -> CFG (Configuration) [Save accross reboots]
  • Select 2-I2C-EEPROM in the Devices option

Save accross reboots (view -> Message View):

• Firmware version: UBX -> MON (Monitor) -> VER (Version)

GPSD

• gpsd
• Packages: gpsd, gpsd-clients

Use of a serial device (eg ttyS0) is prefered over a USB/serial interface (eg ttyUSB0) due to lower latency and PPS availability.

Can be tested with something like (Debug level 4) :

gpsd -N -n -s 9600 -D 4 /dev/ttyS0 /dev/pps0

Configuration in /etc/sysconfig/gpsd, which by default enables detection of USB devices via udev events including creation of a PPS device (/dev/pps0):

USBAUTO="true"

Options can be forced, eg:

OPTIONS="-n -s 9600"
DEVICES="/dev/ttyS0 /dev/pps0"

Check data stream with gpsmon:

gpsmon /dev/ttyS0

when gpsd is not started, or connected to gpsd:

gpsmon

Can show raw data:

gpscat /dev/ttyS0

Enable and start gpsd:

systemctl enable gpsd
systemctl start gpsd

Monitor with:

cgps -s
gpsmon
gpscsv
gpsplot --image gps.png
xgps

Pulse Per Second (PPS)

With PPS output connected to a serial port pin, GPSD should detect it. If it is on GPIO or other serial port, this can be used to create a PPS device:

dnf install pps-tools
modprobe pps_ldisc
setserial -v /dev/ttyS0 low_latency
ldattach PPS /dev/ttyS0

Check PPS signal:

ppstest /dev/pps0
ppscheck /dev/ttyS0

Can set at boot with udev rule (/etc/udev/rules.d/gps.rules):

KERNEL=="ttyS0", SYMLINK+="gps0"
KERNEL=="ttyS0", RUN+="/usr/bin/setserial -v /dev/%k low_latency"
KERNEL=="ttyS0", RUN+="/usr/sbin/ldattach PPS /dev/%k"