GNSS Timing Breakout - ZED-F9T (Qwiic) Hookup Guide

Contributors: Nate, El Duderino
Favorited Favorite 1

Hardware Overview

Let's take a closer look at the ZED-F9T and other hardware present on the SparkFun GNSS Timing Breakout - ZED-F9T (Qwiic).

ZED-F9T GNSS Timing Module

The ZED-F9T is a multi-band GNSS receiver that excels at timing accuracy with the capability to achieve 5 nanosecond (ns) timing accuracy with a standard position lock.

Photo highlighting ZED-F9T module.

The ZED-F9T needs a clear view of the open sky to reduce the timing error to 5ns but requires no external correction. The module also features a Differential Timing Mode where correction data is shared between neighboring ZED-F9T receivers configured in a communication network. When configured properly in a communication network, the module can reduce timing errors to 2.5ns.

The GNSS Timing Breakout specifically uses a ZED-F9T-00B version of the module supporting L1/L2/E5b bands. The ZED-F9T operates on all major constellations (GPS, GLONASS, Galileo and BeiDou) concurrently making it extremely versatile and able to retain its timing precision even the module loses lock with one or more of the visible constellations.

The ZED-F9T also supports the creation of up to four geofence areas, security monitoring and detection systems that, when paired with an IoT controller, can send this data to the user. On top of all that, the ZED-F9T also has an integrated logging system users can configure to store position fixes and arbitrary byte strings in the receiver's Flash memory.

For a detailed overview of the module, these integrated systems and how to use them, refer to the datasheet and integration manual.

Communication Interfaces

The ZED-F9T features standard communication interfaces including USB, two UARTs, SPI and I2C. USB and UART2 have dedicated pins. UART1, SPI and I2C share pins and are selected by the state of the Interface Select pin (labeled D_SEL). The D_SEL pin is left open/"high" by default to enable UART1 and I2C and disable SPI. The shared pins are outlined below:

Photo highlighting communication interfaces.

Default (D_SEL = 1/HIGH)

  • TX
  • RX
  • SDA
  • SCL

Alternate (D_SEL = 0/LOW)

  • SPI CS
Note: The GNSS Timing Breakout routes the SDA/CS and SCL/SPI CLK lines to separate PTH headers labeled for one of the two operation modes (i.e. The pin labeled CS also connects to the pin labeled SDA as well as the SDA line on the Qwiic connector).


The ZED-F9T USB interface is routed to a USB-C connector. The USB acts as both a power input as well as a serial interface to quickly connect the module to u-blox's u-center software to configure the module and view NMEA sentences. See Getting Started with U-Center for more information about using the GNSS Timing Breakout with u-center over USB.


The breakout routes the ZED-F9T's two UARTs (UART1 and UART2) to PTH headers. UART1 acts as a typical serial interface for NMEA sentences or other data. UART2 is a dedicated interface for sending or receiving RTCM correction data. The default settings for both UARTs are 38400 baud, 8-bits, no parity bit, 1 stop bit.


The board connects the ZED-F9T's I2C interface to PTH headers as well as a pair of Qwiic connectors to make it easy to add the GNSS Timing Breakout into a chain of I2C devices using the Qwiic ecosystem. Note, the pull-up resistors for the Qwiic connectors are disabled by default. Close the I2C jumper on the back of the breakout to enable those pull-up resistors.

The default 7-bit unshifted address for the ZED-F9T is 0x42 but is fully adjustable using the appropriate commands. Refer to the Integration Manual for more information.

Note: The pullup resistors on the SDA/SCL lines on the GNSS Timing Breakout are disabled by default. You may need to close th I2C jumper in certain configurations when communicating over I2C.


The ZED-F9T's SPI interface is also broken out but is disabled by default. Enable SPI communication for the ZED-F9T by tying the D_SEL pin to GND/0V. Reminder, enabling the SPI interface disables UART1 and I2C.


Power for the GNSS Timing Breakout can be provided either via a USB-C connection or Qwiic connectors. The breakout also includes outputs for both 5V and 3.3V as well as a backup battery and charging circuit.

Photo highlighting power inputs/outputs

Note: The 5V output PTH only is active when the breakout is powered via USB.

RTC Backup Battery Circuit

The board includes an RTC backup battery circuit to preserve settings and help with quick restarts and warm lock starts. The 1mAh battery can run the backup battery circuit on the ZED-F9T with no external power for roughly one day (24hrs) to preserve stored settings and let the module perform a hot start on restart.

SMA Connectors

The GNSS Timing Breakout has three SMA connectors. One for a GNSS antenna and two for the time pulse signals.

Photo highlighting SMA connectors.

The time pulse signals can be connected to external devices to synchronize their action.

Note: A low cost GNSS antenna will work to get a basic position lock but in order to use the advanced timing and positional accuracy features of the ZED-F9T an antenna with L2 support is required.

Control PTHs

The breakout also routes several control pins to PTHs from the ZED-F9T highlighted below:

Photo highlighting Control PTH connections.

  • RST: ZED-F9T reset pin. Pull the line LOW to reset the module.
  • SAFE: Safeboot pin. Safeboot mode is required for firmware updates and generally should not be used or connected for normal operation.
  • INT: Interrupt I/O pin. Use u-center to configure the pin to bring the module out of deep sleep or use it as an output interrupt for various operations.
  • TP1: Timepulse 1 output signal.
  • TP2: Timepulse 2 output signal.
  • FENCE Geofence output pin. Configure with u-center to go either HIGH or LOW depending on settings when creating a geofence area. Use this to trigger alarms or actions when the module exits the defined geofence area.
  • D_SEL: Interface selection pin. Default is Open/HIGH and selects UART1 and I2C interfaces. Connect to 0V/LOW to select SPI interface.
  • TX_RDY: UART1 Ready to send pin.


The breakout includes four status LEDs highlighted in the image below:

Photo highlighting status LEDs.

  • PWR: Power LED. Illuminates whenever 3.3V is present from either USB or the Qwiic bus.
  • TP1: Timepulse 1 status LED. Pulses on/off in sync with the signal from timepulse 1.
  • TP2: Timepulse 2 status LED. Pulses on/off in sync with the signal from timepulse 2.
  • FEN: Geofence status LED. Will turn on or off when the module exits the geofence area depending on settings.

Solder Jumpers

Never worked with solder jumpers or PCB traces before or would like a refresher? Take a look at our How to Work with Jumper Pads and PCB Traces tutorial.

The GNSS Timing Breakout has eight jumpers on board labeled I2C, MEAS, PWR, TP1, TP2, TP1_LED, TP2_LED, and FENCE. The table below outlines the functionality of each jumper and their default state.

Photo highlighting solder jumpers.
Not pictured: I2C solder jumper on front of the board.

Jumper Label Default State Jumper Function
I2C OPEN Close to enable I2C pullups on bus.
MEAS CLOSED Open to measure current draw by the breakout from VBUS. Note, opening this jumper disables 5V input from USB
PWR CLOSED Completes Power LED circuit. Open to disable Power LED.
TP1 CLOSED Open to isolate the TP1 SMA connector from the TP1 PTH. Helps limit the stray time delay introduced by extra copper or externally soldered devices.
TP2 CLOSED Open to isolate the TP2 SMA connector from the TP2 PTH. Helps limit the stray time delay introduced by extra copper or externally soldered devices.
TP1_LED CLOSED Completes TP1 STAT LED circuit. Open to disable TP1 STAT LED.
TP2_LED CLOSED Completes TP2 STAT LED circuit. Open to disable TP2 STAT LED
FENCE CLOSED Completes the FENCE STAT LED circuit. Open to disable FENCE STAT LED.

Board Dimensions

The GNSS Timing Breakout - ZED-F9T (Qwiic) measures 1.70" x 1.70" (43.18mm x 43.18mm) and includes four mounting holes that fit a 4-40 screw.

Board dimensions