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Meshtastic Mesh Device Nano Edition

A compact Lora device with high efficiency internal compact Lora PCB Antenna, ultra-low noise figure amplifier and internal GPS module. This

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Design for Hiking, Pilot, Skiing, No External Antennas are Required.

Credit Card Size All in One Design with Excellent Mechanical Strength – 10cm*5.8cm*1.6cm, ~80g.

High Efficiency Internal Lora PCB Antenna (VSWR < =1.5 @ 915 MHz) which Ensures the Excellent Coverage.

Additional internal Ultra-low noise figure amplifier for Lora receiving Sensitivity Improvement.

Build-in GPS Module, LNA and patch ceramic antenna. GPS, BDS and GLONASS are supported.

Meshtastic Firmware Preinstalled – Current Firmware Version 1.2.59.

Note: Meshtastic is an opensource project which can send off-grid messaging using inexpensive hardware to create your personal mesh.
More Information: https://meshtastic.org/docs/about
Meshtastic Youtube Channel: https://www.youtube.com/meshtastic

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, Meshtastic firmware[1] can be ported to this design with minor modification. More details are illustrated in the Firmware Section of this document. 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

10cm*5.8cm*1.6cm, ~80g

Typical RF Performance

Lora Max RF Output Power 20 dBm
Lora External RX Ultra-Low Noise Amplifier (LNA) Gain = 15.64 dB, Noise Figure = 0.8dB
VSWR of Lora PCB Antenna (US Edition) < =1.5 @ 915 MHz
Impedance Bandwidth of Lora PCB Antenna (US Edition) 882 MHz to 935 MHz for VSWR < = 2
Positioning And Navigation Module Build-in GPS Module, LNA and patch ceramic antenna. GPS, BDS and GLONASS are supported

Hardware

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 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...

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Discussions

sup wrote 04/06/2022 at 09:35 point

eRuby need 512KiB memory 

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miara wrote 04/04/2022 at 12:54 point

nice device

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Nazwa wrote 04/01/2022 at 20:21 point

0. this is a lot of space , is possible add 18650 power or AA

and meybe solar panel and minimum 9 buttons for menu and meybe other input data?

18650 power is not obligatory , adding step-up from 0-26V i can using this with any auto battery or any lithium battery, external solar panel or vegetables ;-)

1. is possible add external antena (with switch) connector for big antena or outside enclosure or outside room operator. 

2. gps is nice idea but in ukraine i dont need gps , anybody can bombing people. meybe gps have phisical switch on/off

3. meybe ading sound modem for any radio (for example baofeng) and increase mesh network for other ism band.

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Neil Hao wrote 04/01/2022 at 21:14 point

Thank you for your interest in the project, I did consider adding a lithium battery to the product, but finally decided to use a small power bank for power supply in the Nano Edition design. Due to the target of this edition is for Hiking, Pilot, Skiing. No External Antennas are Required. Thus, I hope this edition to be as thin and light as possible, and easy to take on the plane. The lithium battery is restricted in Airports sometime.

This project contains at least 3 editions and this is the first one. The following editions will be station edition and professional edition. The station edition will boost the TX power to at lest to 33dBm to 36dBm with external antenna support. The professional edition will be a handheld device with boosted TX power and internal battery. For both station and professional editions, my goal is to provide stable communication in a complex environment of at least 10km.

For the Nano edition, built-in antenna, solid structure, as light as possible, easy to use in travel, including easy to take on the plane, is the current positioning of this edition. Of course, any power source that can provide 3.3-7.5VDC, including batteries, solar, small power bank can power the Nano Edition via USB Type C.

Each edition has its own positioning and technical difficulties, and challenging these technical difficulties is what I find interesting about this project.

GPS location broadcasts can already be easily turned off in the Meshtastic mobile app. GPS should only receive satellite signals. Could it be that the current missiles can already find GPS receivers?
For the Voice Message, the meshtastic community already pay attentions to the implement, more info: https://meshtastic.discourse.group/t/ptt-voice-transmission/356

At the end, God bless Ukraine!

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Nazwa wrote 04/03/2022 at 16:37 point

Sorry my english is poor.

Increase distance is not neccessary. Trouble with signal is in town. In my opinion mesh is better options than very big signal.

When designing a device, it's important for me to be able to use it without an additional device, laptop or cell phone. Let it be just a few buttons but let it be able to type with T9 dictionary like in old phones. If you don't have any communication then even tapping 10 times to write one letter makes sense ;-)

0. vegetables get less than 3.3 V ;-)

1. I think to myself that the room we are in is not always the best room for the antenna. That goes for people as well as for airplanes. Let's say it is better to place the antenna a little higher or outside, such an external antenna connector could help. (or similar in 3 point. I suggest a sound modem)

2. https://www.reuters.com/world/china/chinas-dji-rejects-claim-that-russian-military-uses-its-drones-ukraine-2022-03-28/

3. http://www.whence.com/minimodem/ meybe in nev edition

I live in Poland, it's the country next door. But for now there is no communication alternative. You are right. God bless Ukraine! 

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