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meshtastic:station

Meshtastic Mesh Device Station Edition

- Optimized RF Design for Maximum Coverage

Neil Hao

Starts from 2022/May/31 to 2022/10/02 18:35 (Last Modification)

:!: Order Yours Today
Official Store https://shop.uniteng.comTemporarily Out of Stock, expected to be in stock on 09-Oct-2022.
Tindie https://www.tindie.com In Stock

:?: Edition Comparisons between our Meshtastic Products

Overview

Meshtastic can send off-grid message using inexpensive hardware to create your personal mesh.

The Station Edition series is a compact Lora device with high power PA (Maximum TX Power: 35dBm@915MHz or 868MHz for Station G1 Edition), Rugged SMA Antenna Socket, rich external IO interface, wide input voltage range (8VDC-20VDC). This series aims to provide the best RF performance in all series with credit card size and rugged construction. Fixed-location base stations and vehicle-mounted base stations are typical application scenarios for this series.

For the firmware, Meshtastic firmware 1.2.65 is preinstalled. Meshtastic Mesh Device Station Edition G1 is merged into the official meshtastic repository on Github starting from firmware 1.3.35.

Dimension

Item Description
Size 10cm*5.8cm*2.1cm
Color Black
Weight~80g

Typical RF Performance

Item Description
Lora Operation Frequency US915MHz and EU868MHz
Lora RF Max Output Power35 dBm @ US915MHz (Station Edition G1)
Lora Power Amplifier Gain 21.5dB @ US915MHz (Station Edition G1)
Lora Power Amplifier P1dB Point 34.5 dBm @ US915MHz (Station Edition G1)
Lora Power Amplifier Noise Figure 0.96dB @ US915MHz (Station Edition G1)
VSWR of Lora Stock Antenna< =2 @ 915 MHz

Typical Application Scenarios

Station Edition could be powered by either USB Type C (PD Protocol with minimum 9V2A is required, 15V2A is recommended due to the requirements of 12V Battery Docker) or 2Pins Socket (Pitch=2.5mm, 8VDC-20VDC, 2A minimum).

Wide voltage input makes the Station Edition ideal as an vehicle-mounted base station and powered directly from the in-vehicle 12V system. The USB Type C power input allows the device to be easily powered by a USB Type C adapter which supports the PD protocol.

Ability to increase transmit power makes it possible to balance communication distance and communication speed. For low power meshtastic devices, usually necessary to set the modem to Long/Slow to obtain the required communication distance, but when using this setting, the communication speed will be very slow, and the continuous sending of messages will also cause timeouts. By increasing the transmit power, we can set the modem to Long/Fast or even Medium/Fast to get a similar experience to Internet-based instant messaging software.

More information about modem setting: https://meshtastic.org/docs/settings/channel#modem_config

Hardware

Schematics

Schematics for 12V Battery Dockermeshtastic_mesh_device_station_edition_12v_battery_docker_28_jul_2022.pdfVersion: 28 Jul 2022
Schematics for Station Edition G1meshtastic_mesh_device_station_edition_12_jun_2022.pdfVersion: 12 Jun 2022

PCB (Station Edition G1)

meshtastic_mesh_device_station_edition_g1_pcb.jpg

No. Description
1 ESP32 WROOM
2 Semtech SX1262 Lora Transceiver
3 Lora Power Amplifier
4 RF Switch
5 SMA Connector for Lora Antenna
6 USB Type C Socket
7 CH9102F USB to UART Bridge
8 Power Input Socket (8VDC-20VDC), 1*2P, Pitch=2.5mm
9 7.5V DCDC
10 3.3V DCDC
11 GPS and Notification Extension Socket, 1*5P, Pitch=1.5mm
12 IO Extension Socket, 1*10P, Pitch=1.5mm
13 LV (Low Voltage) LED Indicator
14 HV (High Voltage) LED Indicator
15 1.3 Inch OLED Screen
16 User Button

Power Status

LV LED (Red) HV LED (Green) Description
ON OFF 3.3V DCDC is working normally, but 7.5V DCDC is not working. Generally, this status indicates the device is powered up by using USB2.0/3.0 which does not support 9V USB Type C PD protocol. For this status, everything should work normally, except the Lora PA. The firmware can be flashed into the device through Type C Port in this status.
ON ON Both 3.3V DCDC and 7.5V DCDC are working normally. Generally, this status indicates the device is powered up by 9V USB Type C PD protocol. For this status, everything should work normally.

Mechanical Design

Similar as Nano Edition, the Station Edition is also constructed by stacking up PCB boards.This method offers a good balance of cost and mechanical strength. The Station Edition employs an aluminum substrate PCB (sliver) as heat sink for high power lora PA. Nonelectrical conductivity high performance thermal grease is applied between the heat sink and the main PCB. meshtastic_mesh_device_station_edition_mechanical_design.jpg Front Side and Bottom Side of the case.


RF Design - Lora (Station Edition G1)

TX PA and Antenna

Conduction Test

Instrument Setup and Device Under Test (DUT) configuration For Instrument Setup, RF Explorer 6G Combo PLUS Spectrum Analyzer and 40 dB Attenuator was used to measure the RF transismission power. Meshtastic firmware firmware_neil_station-g1-1.2.60.bin.zip was flashed into the DUT. Meshtastic Android APP 1.2.64 had been used to control the DUT with channel options = “Long Range / Slow” and Region = “US”.

Measurements When SX1262 TX set to 16 dBm, according to above result, the RF output power was 35.5 dBm, Gain = 19.5dB.

Repeat the measurement process with various SX1262 TX Power (TX Power Setting). The results were summarized in the follow table.

Summary for Conduction Test

Region = “US” Center Frequency = 903.08 MHz
SX1262 TX Power Setting PA Output Power PA Gain Description
17 dBm 35.5 dBm (3.55 W) 18.5dB
16 dBm 35.5 dBm (3.55 W) 19.5dB
15 dBm 35 dBm (3.16 W) 20dB
14 dBm 34.5 dBm (2.82 W) 20.5dB Recommended Setting, 1 dB Compression Point (P1dB)
13 dBm 33.5 dBm (2.24 W) 20.5dB
12 dBm 33 dBm (2 W) 21dB
11 dBm 32.5 dBm (1.78 W) 21.5dB
10 dBm 31.5 dBm (1.41 W) 21.5dB
9 dBm 30.5 dBm (1.12 W) 21.5dB
8 dBm 29.5 dBm (0.89 W) 21.5dB Default Setting, Operation with ISM band

Accessories - 12V Battery Docker

Schematics for 12V Battery Dockermeshtastic_mesh_device_station_edition_12v_battery_docker_28_jul_2022.pdfVersion: 28 Jul 2022

12V Battery Docker is powered by USB TypeC with 15V PD Protocol. It has capability to charge 3*18650 Lithium Batteries with 2A MAX charging current. It also comes with multi protection features, such as Battery Temperature Monitoring, Overcharge/Overdischarge protection, Overcurrent Protection, etc.

While the Station G1 can be powered directly via USB TypeC, the 12V Battery Docker can still be used as backup power, or in scenarios that require mobility.

The motivation for designing the 12V Battery Docker is that most Power Banks cannot supply power to Station G1, because the Power Bank will automatically power off when the load is low in power consumption, especially when PD protocol is used. A few hundred mA would be considered as low in power consumption for most cases.

PCB

No. Description
1 18650 Batteries
2 LED Indicator (Green) for fully charged status
3 LED Indicator (Red) for charging status
4 Li-ion Battery Protection Circuit based on XB3303A
5 NTC Thermistor, muRata NCP18XH103F03RB, 10kΩ ±1% 3380K
6 CN3703 Li-ion Battery Charger Controller
7 USB Type C Socket
8 CN1 Power Output Socket for Station G1, 1*2P, Pitch=2.5mm
9 CN3 is a duplicate of CN2 except IO35, 1*10P, Pitch=1.5mm, please refer to the schematic for more information.
10 CN2 is used to provide battery gauge function for Meshtastic if it is connected to CN2 of Station G1, 1*10P, Pitch=1.5mm
11 Power Switch for Station G1

Note:

  • Green LED and Red LED are OFF at the same time indicates the 12V Battery Docker is powered up by voltage lower than 15V. Generally, this status indicates that the Type C Charger does not support 15V PD Protocol.
  • Green LED and Red LED flashing at the same time indicates at least one of three 18650 batteries is not installed properly or damaged.

Dimension

Item Description
Size 10cm*9.6cm*2.7cm
Color Black
Weight~65g (Without Batteries)

Charging Experiment and Thermal Analysis

According to the charging profile in the CN3703’s datasheet, the highest temperature was expected to occur in the phase with the highest current, thus the highest temperature could be measured during the Constant Current Phase (2A for 12V Battery Docker).

For the charging experiment, three 2000 mAh 18650 Li-ion batteries was installed into 12V Battery Docker. The charging process used 1 hour and 23 minutes to charge the batteries’ voltage from 9.6V to 12.6V. About half an hour was Constant Current Phase, and the rest of the time was Constant Voltage Phase.

Thermal infrared image of the Constant Current Phase (Left) and the Constant Voltage Phase (Right), ambient temperature: 28 degrees in Celsius

Summary for Thermal Analysis

Charging Time: 1 hour and 23 minutes, Ambient Temperature: 28 ℃
Part No. Constant Current Phase Constant Voltage Phase
D1 73.1 ℃ 36.6 ℃
Q1 61.9 ℃ 35.5 ℃
U2,U3,U4 (XB3303A) 51.5 ℃ 31 ℃
U1 (CN3703) 50.8 ℃ 35.5 ℃

Battery Gauge

The battery gauge will be automatically enabled within 30s if CN2 connector is connected to CN2 of Station G1. For Station G1, the battery voltage has been mapped from 0-12.6V.

Details

The battery characteristics are defined at Line 37 to Line 40 in the variant.h.

#define BAT_FULLVOLT 12600
#define BAT_EMPTYVOLT 8200
#define BAT_CHARGINGVOLT 12600
#define BAT_NOBATVOLT 6690

So that, Station G1 is expected to work with three Li-ion 18650 batteries, the full charged voltage = 12.6V, empty voltage = 8.2V.

Known Issues

The firmware will automatically turn off the device when detecting the battery voltage lower then 8.2V. On the other hand, the battery voltage will drop 0.X V when the PA is in transmission mode, because the PA will theoretically consume peak value of 1.2A@7.5V. Therefore, in daily use, you cannot wait for the battery voltage to drop to 8.2V before charging. The exact value of the voltage drop depends on the internal resistance of the batteries. Choosing batteries with lower internal resistance can alleviate the problem.


The Latest Firmware

Pre-compiled Firmware

Version Date Download Description
1.2.65 10-Aug-2022 firmware-station-g1-1.2.65-Patch1.binBattery gauge for 12V Battery Docker is supported. Source Code
1.2.60 28-Jun-2022 firmware_neil_station-g1-1.2.60.bin.zipInitial Release

Software

Android

The Android APP could be downloaded and installed from the Google Play Store: https://play.google.com/store/apps/details?id=com.geeksville.mesh

APP Source Code: https://github.com/meshtastic/Meshtastic-Android/releases

iOS

The iOS APP could be downloaded and installed from following URL: https://meshtastic.org/docs/software/apple

JS/Python/Web Interface

Javascript, Python, Web Interface are also supported by the Meshtastic. More information: https://meshtastic.org/docs/software

Advanced Topics

TX Power Setting

For Meshtastic Firmware 1.2.x

Prerequisites

Execute following command by using Meshtastic CLI, this operation will set the SX1262 TX Power to 14 dBm:

meshtastic --ch-set tx_power 14 --ch-index 0

Output:

Connected to radio
Set tx_power to 14
Writing modified channels to device

Verification, execute following command:

meshtastic --info

Output:

Connected to radio
...
Channels:
  PRIMARY psk=default { "txPower": 14, "modemConfig": "Bw125Cr48Sf4096", "psk": "AQ==" }
...

According to the Summary for Conduction Test, the PA Output Power is expected to be 34.5 dBm (2.82 W), after executing above command.

Real World Testing

FCC Rules and Regulations

Operation with ISM band

Any RF device can transmit encrypted data in the ISM bands without license. However, the maximum transmitter power fed into the antenna should be less than or equal to 30dBm (1W).

ISM Bands
902 to 928 MHz
2.400 to 2.4835 GHz
5.725 to 5.875 GHz

Benefit from high power PA even when operating in the ISM bands. For example, if there is a long coaxial cable between the transmitter and the antenna, the coaxial cable may have considerable insertion loss. At this time, the transmitting power of the transmitter can be increased to ensure exactly 30dBm power feeding into the antenna.

Reference

Operation with Amateur Radio License

Lora 915MHz is exactly 33cm band in the amateur bands. With Amateur Radio License, according to the National Association for Amateur Radio's description, the transmitter can transmit unencrypted data using up to 1500W.

This official document describes in detail how to turn off Meshtastic's encryption: Licensed (HAM) Operation.

How to increase the Lora RF output power: TX Power Setting Copyright: The National Association for Amateur Radio

Reference

Datasheet

Reference

meshtastic/station.txt · Last modified: 2022/10/02 18:35 by neilhao