Assemble USB TTL - BYO-NTP/recipes GitHub Wiki

Since modern mini PCs have no serial ports, add one with a USB to TTL serial adapter. See the USB page for recommendations, tips, and more info.

On this page are assembly instructions for the LEA-M8T, MAX-M8Q, NEO-7M, NEO-6M, and VK-162/U7.

M8T

Assembly

The Huawei GNSS module has a LEA-M8T chip which supports GPS, Galileo, Beidou, and GLONASS. It does not have a USB port, so connect it to a USB to TTL adapter for programming with u-blox u-center.

Pinout:

pin 1 2 3 4 5 6 7 8
desc ANT 3V3/5V VCC/3V3 TXD NC RXD TP1/1PPS NC TP2 GND

This photo shows the pinouts on the board. Note that you MUST cross the TxD and RxD pins. If the module isn't spewing data, check that the pins are reversed. If the antenna supports it (all of mine do), connect 5V to pin 1.

These photos show it wired up:

Bill of Materials

Item Vendor(s) Cost
Huawei WD22UGRC GPS module eBay $25
USB to TTL Serial adapter Amzn $12
SMA-F to SMB-F connector Amzn $5
Active GPS Antenna Amzn $11
2P-F to 1P-F 2mm to 2.54mm Jumper wires Amzn $8
Total $61

M8Q

The Waveshare MAX-M8Q HAT works best on the Pi 4/5 with Pi OS and the Pi 4 with FreeBSD. Here it connects via USB, which works everywhere else.

1. Configure the jumpers to A mode and plug a USB cable into the HAT and a Windows computer with u-blox u-center installed. Configure the GNSS per the recommendations on the gnss page.

2 Configure the jumpers back to B mode and wire up the HAT to a FTDI-chip based usb adapter and plug that into to your NTP server. Here I've wired the HAT to a $2 FTDI USB to serial TTL adapter. Note: the HAT needs 5V connected.

Note: The built-in Silicon Labs CP2102 USB adapter registers and enables NMEA communication but it does not expose PPS. The Silicon Labs drivers on Linux and FreeBSD don't have specific PPS support (bad omen) and reading through the M8Q schematic makes me believe that the PPS signal on this hat isn't wired to the USB adapter at all.

Bill of Materials

Item Vendor(s) Cost
Waveshare MAX-M8Q GNSS hat AliExpress $30
USB to TTL adapter AliExpress $2
6 Jumper wires AliExpress $2
Total $34

The hat is a kit that includes an antenna and the IPEX to SMA pigtail.

7M

Bill of Materials

Item Vendor(s) Cost
Bear GPS module 7M AliExpress $7
USB to TTL adapter AliExpress $2
6 Jumper wires AliExpress $2
Active GPS Antenna, 30dB gain Amzn $11
Total $22

U7

The ublox U7 / VK-162 is an all-in-one including the antenna & USB port, so no assembly is required. The major downside is that it doesn't export PPS. This limits accuracy to the milliseconds range.

6M

Assembly

Bill of Materials

Item Vendor(s) Cost
USB NEO 6M module AliExpress $6
USB to TTL adapter AliExpress $2
Active GPS Antenna Amzn $11
6 Jumper wires AliExpress $2
Total $21

References