Hardware Overview

Design Files

The SparkFun RTK Postcard board's dimensions, pin layout, and connectors are similar to our very popular SparkFun GPS-RTK-SMA Breakout - ZED-F9P (Qwiic) and SparkFun Quadband GNSS RTK Breakout - LG290P (Qwiic). The board features multiple UART ports, which are accessible through the USB-C connector, PTH pins, and 4-pin locking JST connector. Users can also interface with the board through the 19 PTH pins that are broken out around the edge of the board. For the GNSS antenna, an SMA antenna connector is provided on the edge of the board; additionally, users can rework the board to utilize the u.fl connector instead. We also provide two 4-pin JST Qwiic connectors for future use, to operate the board as a peripheral device.

• Design Files

  ---

  • Schematic
  • KiCad Files
  • STEP Files
    • RTK Postcard
    • Enclosure
  • Board Dimensions:
    • 1.70" x 1.70" (43.2mm x 43.2mm)
    • Four mounting holes:
      • 4-40 screw compatible
• 3D ModelDimensions

  RTK Postcard

  Download the *.step File

  Enclosure

  Download the *.step File

  Manipulate 3D Model

  Controls	Mouse	Touchscreen
  Zoom	Scroll Wheel	2-Finger Pinch
  Rotate	Left-Click & Drag	1-Finger Drag
  Move/Translate	Right-Click & Drag	2-Finger Drag

  

  Dimensions of the RTK Postcard.

  Need more measurements?

  For more information about the board's dimensions, users can download the KiCad files for this board. These files can be opened in KiCad and additional measurements can be made with the measuring tool.

  KiCad - Free Download!

  KiCad is free, open-source CAD program for electronics. Click on the button below to download their software. (*Users can find out more information about KiCad from their website.)

  Download

  Measuring Tool

  This video demonstrates how to utilize the dimensions tool in KiCad, to include additional measurements:

  

USB-C Connector

The USB connector is provided to power the board and communicate with either the LG290P GNSS receiver or ESP32 microcontroller. For most users, it will be the primary method for interfacing with the RL Postcard.

USB-C connector on the RTK Postcard.

CH342 Dual UART Converter

The CH342 serial-to-USB converter allows users to interface with the UART1 port of the LG290P GNSS module and UART0 port of the ESP32-Pico module through the USB-C connector. To utilize the CH342, users may need to install a USB driver, which can be downloaded from the manufacturer website.

Tip - USB Drivers

• Windows

  ---

  Download Page for CH343SER.EXE

• MacOS

  ---

  Download Page for CH341SER_MAC.ZIP

Linux

A USB driver is not required for Linux based operating systems.

The UART channels of the CH342 serial-to-USB converter.

Once the USB driver is installed, two virtual COM ports will be emulated and can be utilized as standard COM ports to access the modules:

• ESP32 - Users should select COM port labeled with Channel A (often the lower enumeration).

• LG290P - Users should select COM port labeled with Channel B (often the higher enumeration).

  UART Settings

  • ESP32

    ---

    With the RTK Everywhere firmware, the UART0 port of the ESP32 is configured with the following settings:

    • Baudrate: 115200bps
    • Data Bits: 8
    • Parity: No
    • Stop Bits: 1

  • LG290P

    ---

    With the RTK Everywhere firmware, the UART2 port of the LG290P is configured with the following settings:

    • Baudrate: 460800bps
    • Data Bits: 8
    • Parity: No
    • Stop Bits: 1
    Default Configuration

    The UART ports of the LG290P are configured with the following default settings:

    • Baudrate: 460800bps
    • Data Bits: 8
    • Parity: No
    • Stop Bits: 1
    • Flow Control: None
    • Protocols:
      • NMEA 0183
      • RTCM 3.x

Power

The RTK Postcard only requires 3.3V to power the board's primary components. The simplest method to power the board is through the USB-C connector. Alternatively, the board can also be powered through the other connectors and PTH pins.

RTK Postcard's power connections.

Below, is a general summary of the power circuitry for the board:

• 5V - The voltage from the USB-C connector, usually 5V.
  • Can be utilized as the primary power source for the entire board.
  • When connected to the Portability Shield, this pin used to provide power between the boards. (1)
• 3V3 - 3.3V power rail, which powers the ESP32 Pico-Mini module, LG290P GNSS module, backup battery, and LEDs.
  • Power can also be distributed to/from any of the JST connectors (Qwiic or UART3) or the 3V3 PTH pin.
    • For power that is supplied through these connections, the LG290P has the tightest voltage supply requirement of 3.15–3.45V.
  • A regulated 3.3V is supplied by the RT9080, when powered from the 5V PTH pin or USB connector
    • Input Voltage Range: 3.0 to 5.5V (2)
    • The RT9080 LDO regulator can source up to 600mA.
• 3V3_EN - Controls the power output form the RT9080 voltage regulator.
  • By default, the pin is pulled-up to 5V and to enable the RT9080 output voltage.
• VCC - The voltage from the locking JST-GH connector, which is controlled by the VSEL jumper (3).
  • Used to power an external radio to send or receive RTK corrections.
• GND - The common ground or the 0V reference for the voltage supplies.

1. Details

   When 5V is provided to the RTK Postcard, it will supply power to the Portability Shield and charge the LiPo battery (if connected). To operate properly when charging the battery, the power switch behind the OLED display of the Portability Shield should be in the Off position.

   When powered by a LiPo battery, users must toggle the power switch behind the OLED display of the Portability Shield to the On position. This will allow the battery power to be provided to the RTK Postcard through the 5V pin; and then to its RT9080 LDO.

   Protection diodes are utilized on the boards to independently prevent current feedback and protect the power sources from each other.

2. Brown Out Voltage

   The supply voltage of a LiPo battery will decrease as it is drained. However, before the battery can reach its critical UVLO threshold (~2.8V), the LG290 GNSS module with begin to brown out from an in-use supply voltage of 3.05-3.10V from a battery.

   Battery Capacity

   When selecting a LiPo battery for any combination of the RTK Postcard, Portability Shield, and/or connected radio, users should be aware of the peak current draw of their setup. In theory, most standard LiPo batteries have a maximum discharge rate of 1C (based on the battery capacity).

   \[ 1C = \frac{(1 * Capacity)}{hour} \]

   However, as a battery ages, users may find the effective capacity and discharge rate to degrade to 80% of its original specifications.

   Example

   For example, a LiPo battery with a 400mAh capacity will have a maximum discharge rate of 400mA. However, over time, users may notice its effective use diminish to 320mAh and 320mA respectively.

3. By default, the VSEL jumper is configured to utilize the 3.3V power rail; however, it can be connected to the 5V power rail instead.

   Portability Shield

   When utilizing the 5V power rail of the RTK Postcard, power may be supplied from the LiPo battery from the Portability Shield. This should be taken into consideration when connecting an external radio for RTK corrections.

Info

For more details, users can reference the schematic and the datasheets of the individual components on the board.

Portability Shield

When used in conjunction with the Portability Shield, users should be aware of the following:

• To charge the battery, users must provide adequate power through the 5V pin. This is most easily done by powering the boards from the USB-C connector.
• When operating the boards with the battery power, users must ensure that the switch behind the OLED display is in the On position. This will allow the battery power to feedback to the RTK Postcard through the 5V pin; and over to the RT9080 LDO to provide a regulated 3.3V to its primary components.

Backup Battery

While charged, the backup battery allows the GNSS module to hot/warm start with valid ephemeris data (time and GNSS orbital trajectories) that was stored.

Time to First Fix:

• Cold Start: 28s
• Warm Start: 28s
• Hot Start: 1.7s

  ESP32 Pico-Mini

The brains of the RTK Postcard is an ESP32 Pico-Mini module. The Espressif series of ESP32 modules are a versatile, compact MCU modules with WiFi, BT, and BLE capabilities that target a wide variety of applications. At the core of the ESP32 Pico-Mini module is the ESP32-PICO-V3-02, a System-in-Package device, along with an integrated 8 MB SPI flash, 2 MB SPI PSRAM, and 40 MHz oscillator.

The ESP32 Pico-Mini module on the RTK Postcard.

General Features

• Electrical Characteristics:
  • Operating Voltage: 3.0 - 3.6V
  • Current Consumption:
    • RF Operation: 368mA (peak)
    • Normal Operation: 20-31mA
    • Light-Sleep: 0.8mA
    • Deep-Sleep: 5µA
• Xtensa® Dual-Core 32-bit LX6 Microprocessor (up to 240MHz)
  • 448KB of ROM and 520KB SRAM
  • 8MB SPI Flash
  • 2MB PSRAM
  • 16KB SRAM in RTC
• Operating Temperature: -40 to 85°C

• PCB antenna
• Wi­F 802.11b/g/n
  • Bit Rate: up to 150Mbps (802.11n)
  • Frequency Range: 2412 - 2484MHz
• Bluetooth
  • Bluetooth v4.2 Specification:
    • BR/EDR
    • Bluetooth LE
  • Transmitter Class: 1, 2, and 3
• 27 GPIO (including strapping pins) -
• Supported Peripherals:
  • SD card, UART, SPI, SDIO, I2C, LED PWM, Motor PWM, I2S, IR, pulse counter, GPIO, capacitive touch sensor, ADC, DAC, TWAI® (compatible with ISO 11898-1, i.e. CAN Specification 2.0), Ethernet MAC

Warning

Users should be aware of the following nuances and details of this microcontroller

• The ESP32 Pico-Mini is only compatible with 2.4GHz WiFi networks; it will not work on the 5GHz bands.
• For details on the boot mode configuration, please refer to section 3.3 Strapping Pins of the ESP32 SoC datasheet.

RTK Everywhere Firmware

The RTK Postcard comes pre-programmed with latest version of our RTK Everywhere firmware. However, users are free to reprogram the board as they see fit. For more details about the RTK Everywhere firmware, users can refer to the user manual.

Firmware Download Mode

Users can manually force the board into the serial bootloader with the BOOT button. Please, refer to the Boot Button section below for more information.

Power Modes

The ESP32 Pico-Mini module has various power modes:

• Active - The chip radio is powered on. The chip can receive, transmit, or listen.
• Modem Sleep - The CPU is operational and the clock is configurable. The Wi-Fi/Bluetooth baseband and radio are disabled.
• Light Sleep - The CPU is paused. The RTC memory and RTC peripherals, as well as the ULP coprocessor are running.
• Deep Sleep - Only the RTC memory and RTC peripherals are powered on. The ULP coprocessor is functional.
• Hibernation - Only one RTC timer on the slow clock and certain RTC GPIO active.
• Off - Chip is powered off.

For more information on the power management of the ESP32 Pico-Mini module, pleaser refer to Section 4.4 and Tables: 8 and 9 of the ESP32 Pico-Mini module datasheet.

Peripherals and I/O Pins

The ESP32 Pico-Mini module features 27 multifunctional GPIO pins, of which, 11 I/O pins broken out into PTH pins on the RTK Postcard. Meanwhile, others are utilized to interface with the LG290P GNSS receiver or other components on the board (i.e. USB connector, Qwiic connector, etc.). All of the RTK Postcard PTH pins have a .1" pitch spacing for standard headers and their pin layout is compatible with our Portability Shield.

The peripheral interfaces and I/O pins on the RTK Postcard.

Interfaces:

• UART (x2)
• SPI
• I²C (x2)
• Event Trigger⁴
• RTK Signal
• Interrupt
• PPS Timing Signal
• LG290P Module Reset

ESP32 GPIO	PTH Pin	LG290P IO	Other
GPIO 7	SDA0	I2C_SDA
GPIO 20	SCL0	I2C_SCL
GPIO 13			Qwiic SDA
GPIO 19			Qwiic SCL
GPIO 21		TXD2
GPIO 22		RXD2
GPIO 33	RST	RESET_N
GPIO 34	RTK	RTK_STAT	LED RTK
GPIO 36	PPS	1PPS	LED PPS
GPIO 8	EVENT	EVENT
GPIO 32	SCK
GPIO 25	POCI
GPIO 26	PICO
GPIO 27	CS
GPIO 14	AOI
GPIO 4			LED BT
GPIO 0			LED STAT

General Capabilities

With the pin multiplexing capabilities of the ESP32 SoC, various pins can have several functionalities. For more technical specifications on the I/O pins, please refer to the ESP32 SoC datasheet.

• 18x 12-bit analog to digital converter (ADC) channels
• 3x UARTs (only two are configured by default in the Arduino IDE, one UART is used for bootloading/debug)
• 3x SPI (only one is configured by default in the Arduino IDE)
• 2x I²C (only one is configured by default in the Arduino IDE)
• 2x digital-to-analog converter (DAC) channels
• 16x 20-bit PWM outputs
• 10x Capacitive Touch Inputs

Warning

Users should be aware of the following nuances of the ESP32 Pico-Mini module:

• ⚡ All the GPIO are 3.3V pins.
  • The I/O pins are not 5V-tolerant! To interface with higher voltage components, a logic level adapter is recommended.
• ⚡ There are electrical limitations to the amount of current that the ESP32 Pico-Mini module can sink or source. For more details, check out the ESP32 Pico-Mini module datasheet.
• There are some limitations to the ADC performance, see the Note from the ADC Characteristics section of the ESP32 SoC datasheet.

Programming in Arduino

To program the ESP32 Pico-Mini module in the Arduino IDE, users should select the ESP32 > ESP32 Dev Module from the Board Manager list. Users should also be aware that not all of the features, listed above, will be available in the Arduino IDE. When programming the module with the Arduino IDE, only the following features are available for the board:

• Only one I²C bus is defined.
• Only two UART interfaces are available.
  • UART (USB): Serial
  • RX/TX Pins: Serial1
• Only one SPI bus is defined.

For the full capabilities of the ESP32, the Espressif IDF should be utilized.

General Functions

For digital pins, users will need to declare the pinMode() (link) in the setup of their sketch (programs written in the Arduino IDE) for the pins used.

• Input

  ---

  When configured properly, an input pin will be looking for a HIGH or LOW state. Input pins are high impedance and takes very little current to move the input pin from one state to another.

• Output

  ---

  When configured as an output the pin will be at a HIGH or LOW voltage. Output pins are low impedance; this means that they can provide a relatively substantial amount of current to other circuits.

Additional Functions

There are several pins that have special functionality in addition to general digital I/O. These pins and their additional functions are listed in the tabs below. For more technical specifications on the I/O pins, you can refer to the schematic, ESP32 Pico-Mini module datasheet, ESP32 SoC datasheet, and documentation for the ESP32 Arduino core.

Analog PinsPWM & Analog (DAC) PinsSerial PinsSPI PinsI²C Pins

The ESP32 module provides a 12-bit ADC input on eighteen of its I/O pins. This functionality is accessed in the Arduino IDE using the analogRead(pin) function. (*The available ADC pins are highlighted in the image below.)

Analog input pins on the RTK Postcard.

Tip

To learn more about analog vs. digital signals, check out this great tutorial.

• 

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  Analog vs. Digital

Arduino

By default, in the Arduino IDE, analogRead() returns a 10-bit value. To change the resolution of the value returned by the analogRead() function, use the analogReadResolution(bits) function.

The ESP32 module supports up to sixteen channels of 20-bit PWM (Pulse Width Modulation) outputs on any of its I/O pins. This is accessed in the Arduino IDE using the analogWrite(pin, value) function. (*Any I/O pin can be used for the PWM outputs; the available DAC pins, with true analog outputs, are highlighted in the image below.)

Any I/O pin can be a PWM output, but these are the DAC pins on the RTK Postcard.

Tip

To learn more about pulse width modulation (PWM), check out this great tutorial.

• 

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  Pulse Width Modulation

Arduino

By default, in the Arduino IDE, analogWrite() accepts an 8-bit value. To change the resolution of the PWM signal for the analogWrite() function, use the analogWriteResolution(bits) function.

The ESP32 module provides three UART ports. By default, the UART port for the USB connection (Serial) and the UART port (Serial1) to the LG290P GNSS receiver can be accessed through the Arduino IDE using the serial communication class.

Default UART ports on the RTK Postcard.

Tip

To learn more about serial communication, check out this great tutorial.

• 

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  Serial Communication

Arduino

By default, in the Arduino IDE, the ESP32 Dev Module board definition supports:

• Serial - UART (USB)
• Serial1 - Pins: RX/TX (GPIO 21/GPIO 22)

Tip

We have noticed that with the ESP32 Arduino core, Serial.available() does not operate instantaneously. This is due to an interrupt triggered by the UART, to empty the FIFO when the RX pin is inactive for two byte periods:

• At 9600 baud, hwAvailable takes about 11 ms before the UART indicates that data was received from: \r\nERROR\r\n.

  \[ (bytes + 2) * 1ms = 11ms \]

• At 115200 baud, hwAvailable takes about 1 ms before the UART indicates that data was received from: \r\nERROR\r\n.

  \[ (bytes + 2) * .087ms = 1ms \]

For more information, please refer to this chatroom discussion.

The ESP32 module provides three SPI buses. By default, in the Arduino IDE, the SPI class is configured to utilize pins GPIO 32 (SCK), GPIO 25 (POCI), GPIO 26 (PICO), and GPIO 27 (SS) for its chip select. In order to utilize the other SPI ports or objects, users will need to create a custom SPI object and declare which pins to access.

Default SPI bus connections on the RTK Postcard.

Tip

To learn more about the serial peripheral interface (SPI) protocol, check out this great tutorial.

• 

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  Serial Peripheral Interface (SPI)

Arduino

By default, in the Arduino IDE, the ESP32 Dev Module board definition supports:

SCK	GPIO 32 (SCK)
SDI or POCI	GPIO 25 (MISO)
SDO or PICO	GPIO 26 (MOSI)
CS*	GPIO 27 (SS)

Signal Nomenclature

To comply with the latest OSHW design practices, we have adopted the new SPI signal nomenclature (SDO/SDI and PICO/POCI). The terms Master and Slave are now referred to as Controller and Peripheral. The MOSI signal on a controller has been replaced with SDO or PICO. Please refer to this announcement on the decision to deprecate the MOSI/MISO terminology and transition to the SDO/SDI naming convention.

The ESP32 module module can support up to two I²C buses. By default, in the Arduino IDE, the Wire class is configured to utilize pins GPIO 20 (SDA) and GPIO 7 (SCL). These pins share the same I²C bus with the LG290P GNSS receiver, but not the Qwiic connector. In order to utilize another I²C port, users will need to create a custom Wire object and declare which pins to access.

Default I²C bus connections for the RTK Postcard.

Tip

To learn more about the inter-integrated circuit (I²C) protocol, check out this great tutorial.

• 

  ---

  I2C

Arduino

By default, in the Arduino IDE, the ESP32 Dev Module board definition supports:

SCL0	GPIO 7 (SCL)
SDA0	GPIO 20 (SDA)

  LG290P GNSS

The centerpiece of the RTK Postcard, is the LG290P GNSS module from Quectel. The LG290P is a low-power, multi-band, multi-constellation GNSS receiver capable of delivering centimeter-level precision at high update rates. The built-in NIC anti-jamming unit provides professional-grade interference signal detection and elimination algorithms, which effectively mitigate against multiple narrow-band interference sources and significantly improves the signal reception performance in complex electromagnetic environments. With its performance advantages of high-precision and power consumption, this board is an ideal choice for high-precision navigation applications, such as intelligent robots, UAVs, precision agriculture, mining, surveying, and autonomous navigation.

The LG290P module on the RTK Postcard.

General Features

• Supply Voltage: 3.15 – 3.45V
• Tracking Channels: 1040
• Concurrent signal reception: 5 + QZSS
  • L1, L2, L5, E6 frequency bands
• Sensitivity:
  • Acquisition: -146dBm
  • Tracking: -160dBm
  • Reacquisition: -155dBm
• Antenna Power: External or Internal
• GNSS Constellations and SBAS Systems:
  • USA: GPS + WASS
  • Russia: GLONASS + SDCM
  • EU: Galileo + EGNOS
  • China: BDS + BDSDAS
  • Japan: QZSS + MSAS
  • India: NavIC + GAGAN
• Accuracy of 1PPS Signal: 5ns (RMS)
• Update Rate:
  • Default: 10Hz
  • Max: 20Hz

• Time to First Fix (without AGNSS):
  • Cold Start: 28s
  • Warm Start: 28s
  • Hot Start: 1.7s
• RTK Convergence Time: 5s
• Dynamic Performance:
  • Maximum Altitude: 10000m
  • Maximum Velocity: 490m/s
  • Maximum Acceleration: 4g
• Built-in NIC anti-jamming unit
• Interfaces
  • UART (x3)
    • Baud Rate: 9600–3000000bps
      • Default: 460800bps
    • Protocol: NMEA 0183/RTCM 3.x
  • SPI¹ (x1)
  • I²C¹ (x1)
• Operating temperature: -40°C to +85°C
• Footprint: 12.2mm × 16mm × 2.6mm
• Weight: ~0.9g

Supported Frequency Bands

The LG290P modules are multi-band, multi-constellation GNSS receivers. Below, is a chart illustrating the frequency bands utilized by all the global navigation satellite systems; along with a list of the frequency bands and GNSS systems supported by the LG290P GNSS module.

Frequency bands of the global navigation satellite systems. (Source: Tallysman)

Supported Frequency Bands:

• GPS: L1 C/A, L1C², L5, L2C
• GLONASS: L1, L2
• Galileo: E1, E5a, E5b, E6
• BDS: B1I, B1C, B2a, B2b, B2I, B3I
• QZSS: L1 C/A, L1C², L5, L2C
• NavIC: L5
• SBAS: L1 C/A
• L-band PPP³:
  • PPP: B2b
  • QZSS: L6
  • Galileo HAS: E6

Supported GNSS Constellations:

• GPS (USA)
• GLONASS (Russia)
• Galileo (EU)
• BDS (China)
• QZSS (Japan)
• NavIC (India)

Supported SBAS Systems:

• WASS (USA)
• SDCM (Russia)
• EGNOS (EU)
• BDSBAS (China)
• MSAS (Japan)
• GAGAN (India)

Info

For a comparison of the frequency bands supported by the LG290P GNSS modules, refer to sections 1.2, 1.5, and 1.6 of the hardware design manual.

What are Frequency Bands?

A frequency band is a section of the electromagnetic spectrum, usually denoted by the range of its upper and lower limits. In the radio spectrum, these frequency bands are usually regulated by region, often through a government entity. This regulation prevents the interference of RF communication; and often includes major penalties for any interference with critical infrastructure systems and emergency services.

Frequency bands of the global navigation satellite systems. (Source: ESA)

However, if the various GNSS constellations share similar frequency bands, then how do they avoid interfering with one another? Without going too far into detail, the image above helps illustrate some of the characteristics, specific to the frequency bands of each system. With these characteristics in mind, along with other factors, the chart can help users to visualize how multiple GNSS constellations might co-exist with each other.

For more information, users may find these articles of interest:

• GNSS signal
• GPS Signal Plan
• GLONASS Signal Plan
• GALILEO Signal Plan

GNSS Accuracy

The accuracy of the position reported from the LG290P GNSS module, can be improved based upon the correction method being employed. Currently, RTK corrections provide the highest level of accuracy; however, users should be aware of certain limitations of the system:

• RTK technique requires real-time correction data from a reference station or network of base stations.
  • RTK corrections usually come from RTCM messages that are signal specific (i.e. an RTK network may only provide corrections for specific signals; only E5b and not E5a).
• The range of the base stations will vary based upon the method used to transmit the correction data.
• The reliability of RTK corrections are inherently reduced in multipath environments.

Correction Method	Horizontal	Vertical	Velocity
Standalone	0.7m ~2.3'	2.5m ~8.2'	3cm/s (0.108kph) ~1.2in/s (0.067mph)
RTK	0.8cm (+1ppm) ~0.3"	1.5cm (+1ppm) ~.6"

RTK Corrections

To understand how RTK works, users will need a more fundamental understanding of the signal error sources.

• 

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  Real-Time Kinematics Explained

• 

  ---

  What is Correction Data?

Peripherals and I/O Pins

The LG290P GNSS features several peripheral interfaces and I/O pins. Some of these are broken out as PTH pins on the RTK Postcard; whereas, others are broken out to their specific interface (i.e. USB connector, JST connector, etc.). Additionally, some of their connections are tied to other components on the board.

The peripheral interfaces and I/O pins on the RTK Postcard.

Interfaces:

• UART (x3)
• SPI¹
• I²C¹
• Event Trigger⁴
• Timing Signal
• RTK Signal
• Module Reset

UARTsPPS OutputRTKReset

The LG290P GNSS has three UART ports, which can be operated and configured separately.

The UART ports on the RTK Postcard.

UART Settings

With the RTK Everywhere firmware, the UART ports of the LG290P are configured with the following baudrates:

UART Port	Interface	Baudrate (bps)
UART1	USB-C (CH342)	460800
UART2	ESP32	460800
UART3	JST-GH (Locking)	57600

Default Configuration

The UART ports of the LG290P are configured with the following default settings:

• Baudrate: 460800bps
• Data Bits: 8
• Parity: No
• Stop Bits: 1
• Flow Control: None
• Protocols:
  • NMEA 0183
  • RTCM 3.x

Pin Connections

When connecting to the board's UART pins to another device, the pins should be connected based upon the flow of their data.

Board	RX	TX	GND
UART Device	TX	RX	GND

UART1UART2UART3

UART1 can only be accessed from the USB-C connector, through the CH342 serial-to-USB converter. For Windows and MacOS computers (1), a USB driver must be installed in order to communicate with the LG290P module through the CH342 converter. Once the USB driver is installed:

• Two virtual COM ports are emulated, which can be used as standard COM ports to access the ESP32 or the LG290P modules.
• Users should select COM port listed as Channel B to access the LG290P GNSS receiver.

1. On Linux, the standard Linux CDC-ACM driver is suitable.

UART2 is connected to the ESP32 Pico-Mini.

ESP32	LG290P
IO21: GPIO 21	TXD2
IO22: GPIO 22	RXD2

UART3 is available through the breakout PTH pins or the locking JST connector. The pin layout of the 4-pin locking JST connector is compatible with many of our serial radios and adapter cables.

UART Protocols

UART Protocols

By default, these UART ports are configured to transmit and receive NMEA 0183 and/or RTCM 3.x messages. These messages are generally used for transmitting PNT data; and providing or receiving RTK corrections, respectively. Quectel also implements a system of proprietary messages (PQTM) for users to configure the LG290P that follows a data format similar to the NMEA protocol. The expected structure of these proprietary messages is shown below:

The data structure of Quectel messages for the NMEA protocol.

NMEAPQTMRTCM

A full list of compatible NMEA 0183 v4.11 messages, is provided in section 2.2. Standard Messages of the GNSS Protocol Specification manual. This protocol is used for outputting GNSS data, as detailed by the National Marine Electronics Association organization.

List of Standard NMEA Messages

Message	Type Mode	Message Description
RMC	Output	Recommended Minimum Specific GNSS Data
GGA	Output	Global Positioning System Fix Data
GSV	Output	GNSS Satellites in View
GSA	Output	GNSS DOP and Active Satellites
VTG	Output	Course Over Ground & Ground Speed
GLL	Output	Geographic Position – Latitude/Longitude

A full list of PQTM messages (proprietary NMEA messages defined by Quectel) supported by LG290P, is provided in section 2.3. PQTM Messages of the GNSS Protocol Specification manual. This protocol is used to configure or read the settings for the LG290P GNSS module.

List of Proprietary Quectel Messages

Message	Type Mode	Message Description
PQTMVER	Output	Outputs the firmware version
PQTMCOLD	Input	Performs a cold start
PQTMWARM	Input	Performs a warm start
PQTMHOT	Input	Performs a hot start
PQTMSRR	Input	Performs a system reset and reboots the receiver
PQTMUNIQID	Output	Queries the module unique ID
PQTMSAVEPAR	Input	Saves the configurations into NVM
PQTMRESTOREPAR	Input	Restores the parameters configured by all commands to their default values
PQTMVERNO	Output	Queries the firmware version
PQTMCFGUART	Input/Output	Sets/gets the UART interface
PQTMCFGPPS	Input/Output	Sets/gets the PPS feature
PQTMCFGPROT	Input/Output	Sets/gets the input and output protocol for a specified port
PQTMCFGNMEADP	Input/Output	Sets/gets the decimal places of standard NMEA messages
PQTMEPE	Output	Outputs the estimated position error
PQTMCFGMSGRATE	Input/Output	Sets/gets the message output rate on the current interface
PQTMVEL	Output	Outputs the velocity information
PQTMCFGGEOFENCE	Input/Output	Sets/gets geofence feature
PQTMGEOFENCESTATUS	Output	Outputs the geofence status
PQTMGNSSSTART	Input	Starts GNSS engine
PQTMGNSSSTOP	Input	Stops GNSS engine
PQTMTXT	Output	Outputs short text messages
PQTMCFGSVIN	Input/Output	Sets/gets the Survey-in feature
PQTMSVINSTATUS	Output	Outputs the Survey-in status
PQTMPVT	Output	Outputs the PVT (GNSS only) result
PQTMCFGRCVRMODE	Input/Output	Sets/gets the receiver working mode
PQTMDEBUGON	Input	Enables debug log output
PQTMDEBUGOFF	Input	Disables debug log output
PQTMCFGFIXRATE	Input/Output	Sets/gets the fix interval
PQTMCFGRTK	Input/Output	Sets/gets the RTK mode
PQTMCFGCNST	Input/Output	Sets/gets the constellation configuration
PQTMDOP	Output	Outputs dilution of precision
PQTMPL	Output	Outputs protection level information
PQTMCFGODO	Input/Output	Sets/gets the odometer feature
PQTMRESETODO	Input	Resets the accumulated distance recorded by the odometer
PQTMODO	Output	Outputs the odometer information
PQTMCFGSIGNAL	Input/Output	Sets/gets GNSS signal mask
PQTMCFGSAT	Input/Output	Sets/gets GNSS satellite mask
PQTMCFGRSID	Input/Output	Sets/gets the reference station ID
PQTMCFGRTCM	Input/Output	Sets/gets RTCM

A full list of compatible RTCM v3 messages, is provided in section 3. RTCM Protocol of the GNSS Protocol Specification manual. This protocol is used for transferring GNSS raw measurement data, as detailed by the Radio Technical Commission for Maritime Services organization.

List of Supported RTCMv3 (MSM) Messages

Message	Type Mode	Message Description
1005	Input/Output	Stationary RTK Reference Station ARP
1006	Input/Output	Stationary RTK Reference Station ARP with height
1019	Input/Output	GPS Ephemerides
1020	Input/Output	GLONASS Ephemerides
1041	Input/Output	NavIC/IRNSS Ephemerides
1042	Input/Output	BDS Satellite Ephemeris Data
1044	Input/Output	QZSS Ephemerides
1046	Input/Output	Galileo I/NAV Satellite Ephemeris Data
1073	Input/Output	GPS MSM3
1074	Input/Output	GPS MSM4
1075	Input/Output	GPS MSM5
1076	Input/Output	GPS MSM6
1077	Input/Output	GPS MSM7
1083	Input/Output	GLONASS MSM3
1084	Input/Output	GLONASS MSM4
1085	Input/Output	GLONASS MSM5
1086	Input/Output	GLONASS MSM6
1087	Input/Output	GLONASS MSM7
1093	Input/Output	Galileo MSM3
1094	Input/Output	Galileo MSM4
1095	Input/Output	Galileo MSM5
1096	Input/Output	Galileo MSM6
1097	Input/Output	Galileo MSM7
1113	Input/Output	QZSS MSM3
1114	Input/Output	QZSS MSM4
1115	Input/Output	QZSS MSM5
1116	Input/Output	QZSS MSM6
1117	Input/Output	QZSS MSM7
1123	Input/Output	BDS MSM3
1124	Input/Output	BDS MSM4
1125	Input/Output	BDS MSM5
1126	Input/Output	BDS MSM6
1127	Input/Output	BDS MSM7
1133	Input/Output	NavIC/IRNSS MSM3
1134	Input/Output	NavIC/IRNSS MSM4
1135	Input/Output	NavIC/IRNSS MSM5
1136	Input/Output	NavIC/IRNSS MSM6
1137	Input/Output	NavIC/IRNSS MSM7

From the module, the PPS output signal is a 3.3V signal output that can be access through the SMA connector and/or the PPS PTH pin. The signal is also connected to the PPS LED, which can be used as a visual indicator for its operation.

The timing signal's outputs on the RTK Postcard.

Jumpers

See the Jumpers section for more details.

• There is a jumper attached to the PPS PTH pin. When cut, it disconnects the pin from the PPS signal.
• There is a jumper attached to the PPS LED. For low power applications, the jumper can be cut to disable the PPS LED.

Use Case

• Users could use this signal in conjunction with the event pins to synchronize two modules with each other.
• Users could use this signal to create their own Stratum 0 source for the NTP on a primary time server.

The RTK PTH pin operates as both the RTK_STAT status indicator for the RTK positioning and ANT_ON power control for the external LNA or active antenna power. The pin is also connected to the RTK LED, which can be used as a visual indicator for its operation.

The RTK signal's outputs on the RTK Postcard.

RTK_STATANT_ON

In this configuration, the pin is set to a high level at startup.

1. If the pin output is high, it indicates the module has entered the RTK fixed mode.
2. If the pin output is low, it indicates that the module exited the RTK fixed mode.
3. If the pin outputs an alternating pin level, it indicates that the module received the correct RTCM data and did not enter the RTK fixed mode.

In this configuration, the pin is used to control the external LNA or active antenna power supply.

• When the pin is high, the antenna is powered.
• When the pin is low, the antenna is not powered.

Jumpers

See the Jumpers section for more details.

• There is a jumper attached to the RTK LED. For low power applications, the jumper can be cut to disable the RTK LED.

The RST pin can be used to reset the LG290P module if it enters an abnormal state. To reset the GNSS module, the pin must be low for more than 100ms.

The RST pin on the RTK Postcard.

Buttons

There are two buttons on RTK Postcard; a RST and BOOT button.

RST and BOOT buttons on the RTK Postcard.

ResetBoot

Reset Button

The RST (reset) button allows users to reset the program running on the ESP32 Pico-Mini module without unplugging the board.

Boot Button

The BOOT button can be used to force the board into the serial bootloader. Holding down the BOOT button, while connecting the board to a computer through its USB-C connector or resetting the board will cause it to enter the Firmware Download mode. The board will remain in this mode until it power cycles (happens automatically after uploading new firmware) or the RST button is pressed.

1. Hold the BOOT button down.
2. Reset the MCU.
   • While unpowered, connect the board to a computer with through the USB-C connection.
   • While powered, press the RST button.
3. Release the BOOT button.
4. After programming is completed, reboot the MCU.
   • Press the RST button.
   • Power cycle the board.

GNSS Antenna Connectors

While there are two GNSS antenna connectors, only the SMA connector is connected to the LG290P GNSS module by default. If users wish, they can rework the 0402 resistor on the antenna trace to utilize the u.fl connector instead.

The SMA connector for an external GNSS antenna on the RTK Postcard.

The u.fl connector for the PPS output from the RTK Postcard.

Antenna Specifications

• Passive antennas are not recommended for the LG290P GNSS module.
• To mitigate the impact of out-of-band signals, utilize an active antenna whose SAW filter is placed in front of the LNA in the internal framework.
  • DO NOT select and antenna with the LNA placed in the front.
• There is no need to inject an external DC voltage into the SMA connector for the GNSS antenna. Power is already provided from the LG290P module for the LNA of an active antenna.

JST Connector

The RTK Postcard features a 4-pin JST GH connector, which is polarized and locking. Users can access the pins of the UART3 port, through the JST connector with our breadboard cable(1) or through the PTH pins. The pin layout of the JST connector is compatible with many of our serial radios and adapter cables.

1. 

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   Breadboard to JST-GHR-04V Cable - 4-Pin x 1.25mm Pitch
   CAB-17240

The JST connector on the RTK Postcard.

Default Baudrate

• The default bardrate of the UART ports from the LG290P is 480600bps, with the factory settings.
• The default bardrate of the UART3 port from the LG290P (for the locking JST connector) is 57600bps, when utilizing the pre-programmed RTK Everywhere firmware.

Pin Connections

Pin Connections

When connecting the RTK Postcard to other products, users need to be aware of the pin connections between the devices.

Pin Number	1 (Left Side)	2	3	4
Label	VCC	TX3	RX3	GND
Function	Voltage Output - Default: 3.3V - Selectable: 3.3V or 5V	UART3 - Receive	UART3 - Transmit	Ground

When connecting the RTK Postcard to our radios, the pin connections should follow the table below. If the flow control is not enabled, the only the RX, TX, and GND pins are utilized.

Board	RX	TX	GND
Radio	TX	RX	GND

As documented in the LoRaSerial product manual, the pin connections between a host system (i.e. RTK Postcard) and the LoRaSerial Kit radio is outlined in the image below.

The COM ports on the RTK Postcard.

Status LEDs

There are five status LEDs on the RTK Postcard. The table below, lists the pin connections between these LEDs, the LG290P GNSS module, and the ESP32 Pico-Mini module. For details about their operation, please refer to the list at the underneath.

LED	ESP32 GPIO	LG290P IO
BT	GPIO 4	---
RTK	GPIO 34	RTK_STAT
PPS	GPIO 36	1PPS
PWR	N/A	N/A
STAT	GPIO 0	---

The status LED indicators on the RTK Postcard.

• BT - Bluetooth (Blue)
  • With the RTK Everywhere firmware, this LED indicates when the ESP32 Pico-Mini module is paired with a Bluetooth device
• RTK - RTK Mode (White)
  • Indicates when an RTK fix has been established or when the correct RTCM data is being received (see the RTK section)
• PPS - Pulse-Per-Second (Yellow)
  • Indicates when there is a pulse-per-second signal (see the PPS Output section)
• PWR - Power (Red)
  • Turns on once 3.3V power is supplied to the board
• STAT - Status (Green)
  • With the RTK Everywhere firmware, this LED indicates the operation mode

Jumpers

Never modified a jumper before?

Check out our Jumper Pads and PCB Traces tutorial for a quick introduction!

• 

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  How to Work with Jumper Pads and PCB Traces

There are eight jumpers on the back of the board that can be used to easily modify the hardware connections on the board. From which, there are five jumpers that control power to the status LEDs on the board. By default, all the jumpers are connected to power the status LEDs. For low power applications, users can cut the jumpers to disconnect power from each of the LEDs.

The jumpers on the back of the RTK Postcard.

• I2C-EXT - This jumper can be cut to disconnect the pull-up resistors on the SCL_1 and SDA_1 connections of the Qwiic connectors.
• SHLD - This jumper can be cut to disconnect the shielding of the USB-C connector from the GND plane of the board
• VSEL - This jumper can be modified to configure/disconnect the VCC pin of the 4-pin locking JST connector to/from 3V3 or 5V power rails.
  • Users should also keep in mind that connecting the jumper to the 5V power rail, could include the voltage provided by the LiPo battery from the Portability Shield.
• STAT - This jumper can be cut to remove power from the green LED, indicating the operational status for the RTK Everywhere firmware.
• PWR - This jumper can be cut to remove power from the red, power LED.
• PPS - This jumper can be cut to remove power from the yellow LED, which is connected to the PPS signal.
• RTK - This jumper can be cut to remove power from the white LED, indicating RTK fix or operation in RTK mode.
• BT - This jumper can be cut to remove power from the blue LED, indicating Bluetooth pairing for the RTK Everywhere firmware.

Default Configuration

• By default, PPS signal is connected to the PPS pin.
• By default, the VSEL jumper is connected to 3V3 pad for a regulated 3.3V output on the 4-pin JST-GH connector.
• By default, the BT_VCC jumper provides a regulated 3.3V output to the BlueSMiRF header.

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1. Feature Under Development

   Currently, only the UART interface is supported by the module. Support for the I²C and SPI interfaces are still under development.

   ↩↩↩↩

2. Feature Under Development

   Support for the L1C frequency band has not been implemented.

   ↩↩

3. Feature Under Development

   Corrections for some of the PPP services have not been implemented.

   ↩

4. Feature Under Development

   The event trigger has not been implemented.

   ↩↩