Unicore GPS modules

Several users have chosen alternative GPS RTK modules with chips by Unicore:

• UM960
• UM980
• UM982

These chips are sold in different variants. Some come with a USB-C socket (so they can be connected directly to the Raspberry Pi). Some have different antenna socket (which need an SMA F to MMCX M90 cable).

Compared to the ArduSimple simpleRTK2B, they're a bit cheaper and support triple-band frequencies.

Documentation

Command reference

Software

The vendor offers UPrecise to check all status details and configure the receiver. The UI is pleasing and has many features, but also quite some bugs. The download requires creating a free account.

Configuration

Receiver

The following configuration works quite well. COM3 is used when connected via USB.

FRESET
CONFIG COM3 460800
MODE ROVER UAV
GPGGA 0.1
GPGSV 1
GPRMC 1
GPGSA 1
GPVTG 1
SAVECONFIG

These lines can be pasted into UPrecise after connecting to the receiver. Theoretically, you can also connect directly to the receiver's TTY, but make sure to send CR+LF (\r\n) line endings, otherwise the commands won't be recognized.

OpenMower (mower_config.txt)

export OM_GPS_PROTOCOL="NMEA"
export OM_GPS_PORT="/dev/ttyUSB0"
export OM_GPS_BAUDRATE="460800"

Rebooting

Sometimes the receiver just can't get a fix. Then it might be helpful to reboot it. There are three buttons in UPrecise, which execute these commands:

Button	Command
Hot Start	RESET
Warm Start	RESET EPHEM
Cold Start	RESET EPHEM ALMANAC IONUTC POSITION

See also section 8.3 ("Reset") in the command reference. In contrast to the FRESET command, these command don't wipe the configuration.