GPS Module

HW-595 Board

uBlox GPS Board

• Based on uBlox NEO-6M-0-001
• 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
• LED:
  • Constant: Searching
  • Blink 1s: Position fix
• 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 can be reconfigured as a frequency reference:

• Send PPS to UART via CTS
• 0.25 Hz - 10 MHz
• Configure in u-Center here
• Output has high frequency accuracy, but suffers from jitter except at a few specific frequencies

Software

U-Center

• U-Center
• To change baud rate: View -> Messages View; unfold UBX -> CFG (Config) -> PRT (Ports); Choose the Baudrate option, and Send
• Save for restart: Unfold UBX -> CFG (Config) -> CFG( Configuration); Select 2-I2CEEPROM in the Devices option. Send to save the configuration.

GPSD

• gpsd
• Packages: gpsd, gpsd-clients

Use of a serial device (eg ttyS0) is prefered over a USB/serial interface (eg ttyUSB0).

Check data stream with gpsmon:

gpsmon /dev/ttyS0

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

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

Should auto-detect which UART is GPS connected to (baud rate, etc, with no configuration) with:

USBAUTO="true"

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"