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meshtastic:nano

Meshtastic Mesh Device Nano Edition

- Optimized RF Design for Maximum Coverage

Neil Hao

Starts from 2022/Mar/16 to 2022/11/13 16:43 (Last Modification)

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Overview

The Nano Edition series is a compact Lora device with high efficiency internal compact Lora PCB Antenna, ultra-low noise figure amplifier and internal GPS module. This series aims to balance the RF performance, size, rugged construction and power consumption.

For the firmware, all Nano Edition devices come with pre-installed Meshtastic firmware[1]. Meshtastic Mesh Device Nano Edition G1 also had been supported by the official meshtastic repository on Github. More detials could be found in the The Latest Firmware section. Meshtastic can send off-grid message using inexpensive hardware to create your personal mesh.

The coverage of this credit card size Lora device was tested in the urban area which full of more than 150m skyscraper towers. In the experiment (TX:20dBm, Freq:915Mhz, Medium/Slow), 773m communication distance had been tested, no timeout or re-transmitting occurred. According to the link budget, this system could reach far further than 773m. More details are illustrated in the Real World Testing Section of this document.

Dimension

Item Description
Size 10cm*5.8cm*1.6cm
Color Black
Weight~80g

Typical RF Performance

Item Description
Lora Operation Frequency 915 MHz
Lora Max RF Output Power20 dBm (Nano Edition G1)
Lora External RX Ultra-Low Noise Amplifier (LNA) Gain = 15.64 dB, Noise Figure = 0.8dB (Nano Edition G1)
VSWR of Lora PCB Antenna< =1.5 @ 915 MHz
Impedance Bandwidth of Lora PCB Antenna882 MHz to 935 MHz for VSWR < = 2
Positioning And Navigation ModuleBuild-in GPS Module, LNA and patch ceramic antenna. GPS, BDS and GLONASS are supported

Hardware

Schematics

Schematics for Nano Edition G1meshtastic_mesh_device_nano_edition_17_mar_2022.pdfVersion: 21 Jan 2022

PCB (Nano Edition G1)

No. Description
1 ESP32 WROOM
2 Active Buzzer
3 Semtech SX1276 Lora Transceiver
4 USB Type C Socket
5 CH9102F USB to UART Bridge
6 Ultra-Low Noise Amplifier (LNA)
7 RF Switch (RF Performance Measurement)
8 915Mhz Lora PCB Antenna
9 ATGM336H-5N-71 Whole Constellation Positioning and Navigation Module
10 GPS Ceramic Patch Antenna
11 User Button
12 1.3 Inch OLED Screen

Mechanical Design

The strategy for the mechanical design is balancing the initial cost and the case BOM cost.

The Plastic case has not been chosen due to relative high initial cost on Plastic Injection Mold. Plastic case usually require a large volume of sales to dilute the mold cost.

Metal cases have relative low initial cost but not easy to deal with the internal antenna.

Thus, the case is constructed by stacking up PCB boards.This method offers a good balance of cost and mechanical strength. Front Side and Bottom Side of the case.


RF Design - Lora (Nano Edition G1)

TX Circuit and Antenna

Conduction Test

Instrument Setup and Device Under Test (DUT) configuration Click to Enlarge

For conduction test, an IPEX connector needs to be soldered on P1, 0 Ohm 0402 resistor R8 also needs to be moved to the place of R9.

For Instrument Setup, RF Explorer 6G Combo PLUS Spectrum Analyzer and 30 dB Attenuator (:!: Order Yours Today) was used to measure the RF transismission power.

Measurements When TX set to 14dBm, according to above result, the RF output power was -14.5+30=15.5 dBm

When TX set to 20dBm, according to above result, the RF output power was -10.5+30=19.5 dBm

Summary for Conduction Test

TX Setting Measured Output Power
14 dBm15.5 dBm
20 dBm19.5 dBm
Antenna Measurement

Instrument Setup and Device Under Test (DUT) Configuration Click to Enlarge

For Antenna Measurement, an IPEX connector needs to be soldered on P1, additional one 0 Ohm 0402 resistor also needs to be soldered on the place of R9. C15 need to be removed.

For Instrument Setup, low cost Nano VNA is already sufficient for this measurement. All metal around the antenna will have a notable effect on the antenna performance, so the DUT should be suspended in the air during the measurement. During the test, the antenna must be installed inside the product, as close as possible to the final use state, because the product casing also affects the antenna parameters. The calibration plane of the VNA should be at least at the IPEX connector, port extension may be used for VNA calibration.

Measurements S11 and VSWR for the internal compact Lora PCB Antenna.

Summary for Antenna Measurement

Item Measured Value
S11 @ 915.35 MHz-16.17 dB
S11 @ 907.91 MHz-18.61 dB
VSWR @ 915.35 MHz1.368
Impedance Bandwidth882 MHz to 935 MHz for VSWR < = 2
S1P File meshtastic_mesh_device_nano_edition_g1_antenna_measurement_s11.zip

RX LNA

An Ultra-Low Noise Amplifier (LNA) is placed in the RX link for Receiver Sensitivity improvement. More details about this concept could be found in the WIKI of our previous project, Compact Lora Messenger. The typical noise figure is 0.8dB for this LNA design.

The fixture (right hand side) was designed for LNA evaluation.

Measurements Summary for RX LNA Measurement

Item Measured Value
S11 @ 915.5MHz -15.25 dB
S21 @ 915.5MHz 15.64 dB

RF Design - GPS

Positioning and Navigation circuit is designed based on ATGM336H-5N high performance whole constellation positioning and navigation module with AT2659 LNA and patch ceramic antenna. The datasheet of ATGM336H-5N could be downloaded at the datasheet section of this document.

A VIA structure for RF signal chain was designed for connecting the GPS module and the Patch Antenna. The Patch Antenna needs to be connected to the module by using microstrip line on the bottom layer since for microstrip line on the top layer, hard to control the distance between the patch ceramic antenna and the PCB below it.The distance affects the impedance of microstrip.

Measurements for the VIA Click to Enlarge

Measurement: left hand side; Top layer: upper right; Bottom layer: lower right.

Summary for the VIA Measurement

Item Measured Value
S11 @GPS L1 band (1575.42 MHz) -22.13 dB
S21 / Insertion Loss @GPS L1 band (1575.42 MHz) -0.1982 dB
Impedance @GPS L1 band (1575.42 MHz) 44.481-j*4.9

Notification Circuit

An active buzzer is connected to the ESP32's IO13.

The Latest Firmware

Meshtastic Mesh Device Nano Edition G1 had been supported by the official meshtastic repository on Github from firmware version 1.2.61. Thus, the latest firmware could be downloaded from the meshtastic project’s releases page: https://github.com/meshtastic/Meshtastic-device/releases

 Firmware file: firmware-nano-g1-1.x.x.bin

The Fimware may also be updated by using Meshtastic GUI Installer. Meshtastic GUI Installer is a cross platform, easy to use GUI for installing Meshtastic firmware.

More Information about the official firmware support: https://meshtastic.org/docs/hardware/supported/nano-g1

Firmware Less Than Or Equal To Meshtastic 1.2.59

For the old firmwares less than or equal to Meshtastic 1.2.59, Meshtastic firmware[1] can be ported to this design with minor modification. Unless there are special reasons, it is not recommended to use old firmwares, these firmwares may not be compatible with the latest version of mobile APP or other PC softwares.

Pre-compiled Firmware

Version Date Download Description
1.2.59 25-Mar-2022 firmware_neil_nano_g1-1.2.59.bin.zip Source Code
1.2.57 13-Mar-2022 firmware_neil_nano_g1-1.2.57.bin.zip Initial Release

Porting from the source code

The firmware is ported based on the source code of tbeam with minor modification. The porting process is briefly described in the following section.

1.Creating a build environment (Meshtastic's Official Document)

Note: You may want to use 1.2-legacy branch for less bugs.

2. In the file tbeam/variant.h

 Modify 
 #define BUTTON_PIN 38     // The middle button GPIO on the T-Beam
 To
 #define BUTTON_PIN 36     // The middle button GPIO on the T-Beam
 Comment out the line
 #define AXP192_SLAVE_ADDRESS 0x34

3.In the file configuration.h

 Uncomment the line
 #define USE_SH1106

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

Please be aware, the operations described in this section are dangerous because invalid options can physically damage or destroy your hardware. Ensure that you fully understand the schematic for your particular device before trying this. Use at your own risk.

Setting TX Power to 20 dBm

For Meshtastic Firmware 2.x.x

Execute following command by using Meshtastic CLI which supports Firmware 2.x.x:

meshtastic --set lora.tx_power 20

Output:

Connected to radio
Set lora.tx_power to 20
Writing modified preferences to device

For Meshtastic Firmware 1.2.x

Execute following command by using Meshtastic CLI 1.2.95 which supports Firmware 1.2.x:

meshtastic --ch-set tx_power 20 --ch-index 0

Output:

Connected to radio
Set tx_power to 20
Writing modified channels to device

Enabling ext_notification_plugin

For Meshtastic Firmware 2.x.x

You will be alerted by the Active Buzzer when receiving an incoming message.

Execute following command by using Meshtastic CLI:

meshtastic --set external_notification.enabled true

Output:

Connected to radio
Set external_notification.enabled to true
Writing modified preferences to device

Execute following command by using Meshtastic CLI:

meshtastic --set external_notification.alert_message true

Output:

Connected to radio
Set external_notification.alert_message to true
Writing modified preferences to device

Execute following command by using Meshtastic CLI:

meshtastic --set external_notification.output_ms 100

Output:

Connected to radio
Set external_notification.output_ms to 100
Writing modified preferences to device

Execute following command by using Meshtastic CLI:

meshtastic --set external_notification.active true

Output:

Connected to radio
Set external_notification.active to true
Writing modified preferences to device

Re-power the device, the incoming new message will result in 100ms alert.

More details: https://meshtastic.org/docs/settings/moduleconfig/external-notification

Real World Testing

TX:20dBm, Freq:915Mhz, Medium/Slow

The coverage of this credit card size Lora device was tested in the urban area which full of more than 150m skyscraper towers. In the experiment (TX:20dBm, Freq:915Mhz, Medium/Slow), 773m communication distance had been tested, no timeout or re-transmitting occurred. According to the link budget, this system could reach far further than 773m. The user experience of the Medium/Slow option was very close to IM software, with no noticeable communication delays.

Screenshots and Photos

TX:20dBm, Freq:915Mhz, Long/Slow

The coverage of this credit card size Lora device was tested in the urban area which full of more than 150m skyscraper towers. In the experiment (TX:20dBm, Freq:915Mhz, Long/Slow), 2000m communication distance had been tested. At the distance of 1800 meters, the device was completely normal. At the distance of 2000 meters, the function of sending messages was still normal, but the device status and location information could not be updated normally. The Long/Slow option had significant communication delays.

Screenshots and Photos

Datasheet

Part No.DatasheetDescription
ATGM336H-5Natgm336h-5n.pdfHigh performance whole constellation positioning and navigation module

Reference

  1. Meshtastic-device . Retrieved Mar 17, 2022, from https://github.com/meshtastic/Meshtastic-device
meshtastic/nano.txt · Last modified: 2022/11/13 16:43 by neilhao