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
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
GPGST 1
SAVECONFIGThese 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.