MAX-M8Q GNSS HAT for Raspberry Pi – GPS, GLONASS, BeiDou & Galileo, 2.5 m Accuracy, u-blox M8

In short

A satellite positioning board that plugs onto a Raspberry Pi and tells it where it is, to within about 2.5 metres. It tracks four satellite networks instead of just GPS, so it keeps working in places a basic GPS module gives up — under trees, between tall buildings, or in a moving vehicle. An external antenna is included.

Who it is for

Pick this board if your project needs to know its own location or the exact time, and needs to be right about it. Common uses:

• Vehicle and asset trackers that must hold a fix while moving
• Weather balloons and rocketry, since it is rated to 50,000 metres and 500 metres per second
• Drone and rover navigation
• Precise time servers, using the board's very accurate timing pulse
• Geo-fencing, where the board itself can flag when it crosses a boundary you set

Why four satellite networks matters

A basic GPS module listens to one network. This board uses a u-blox MAX-M8Q receiver, which listens to up to three at once, chosen from GPS, GLONASS, BeiDou and Galileo.

More networks means more satellites overhead at any moment. That is what keeps the position steady when the sky is partly blocked. In an open field the difference is small. In a city street, under tree cover, or in a car, it is the difference between a stable reading and one that wanders or drops out.

It also reads augmentation signals, which are correction broadcasts that improve accuracy in regions that provide them. The supported ones are SBAS, QZSS, IMES and D-GPS.

How accurate is it

• Position: about 2.5 metres using GPS, or GPS and GLONASS together. About 3 metres on BeiDou, 4 metres on GLONASS alone. These figures are CEP, meaning half of all readings fall within that distance of the true position.
• Speed: accurate to 0.05 metres per second
• Direction of travel: accurate to 0.3 degrees
• Timing pulse: accurate to 30 nanoseconds, and can be set anywhere from 0.25 Hz to 10 MHz

How quickly it finds a fix

Time to first fix is how long the board takes to work out where it is after being switched on.

• 1 second if it was recently powered on and still remembers the satellites
• 2 seconds if the Pi has internet and can hand it satellite data first, a feature called A-GNSS
• 26 seconds from completely cold, with no stored information

It can update its position up to 18 times a second, and does so once a second out of the box. Tracking sensitivity is −167 dBm, which is a measure of how faint a satellite signal it can still lock onto — lower numbers are better, and this is a strong figure.

Connecting it

• Raspberry Pi: sits on the standard 40-pin header. Also works with the Jetson Nano.
• From a computer: there is a USB-to-serial chip on board (a CP2102), so you can plug it into a PC to test it or configure it with u-blox's free u-center software.
• Other microcontrollers: the serial (UART) and I2C connections are broken out for use with Arduino, STM32 and similar.
• Serial speed: 4800 to 921600 baud, running at 9600 by default. I2C runs up to 400 kHz.
• Data formats: NMEA 0183 version 4.0, with versions 2.1, 2.3 and 4.1 also selectable, plus UBX and RTCM 2.3.

Power and physical details

• Power: 5 V, taken from the Pi header
• Current draw: under 40 mA for the whole board
• Operating temperature: −40 °C to +85 °C
• Board size: 65 × 30.5 mm
• Movement limits: up to 4 g acceleration, 500 metres per second, 50,000 metres altitude

What you get in the box

• MAX-M8Q GNSS HAT
• External GPS antenna
• USB-A to Micro-B cable
• Two Raspberry Pi mounting screws
• One 2 × 20-pin female header

The included antenna is the active external type. If the board is going inside a case or a vehicle, use it rather than relying on a bare chip antenna — the fix will be noticeably better.