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Second-Generation Mesh Extender

DFAT Funded Refinement of Mesh Extender

As part of the Pacific Humanitarian Challenge (PHC) grant that we have received from the Australian Department of Foreign Affairs and Trade (DFAT), we are in the process of redesigning the Mesh Extender for use in tropical-maritime environment, and generally addressing the productisation of the Mesh Extender, so that we can easily produce robust and reliable Mesh Extenders that are required for the grant activities, but also so that after the grant, Mesh Extenders can be readily produced for other potential users.

Software Development

The primary repository for the Mesh Extender is:

If you wish to develop on the individual packages, then these are the relevant repositories:

Specifications

  • Full custom-designed injection-moulded housing.
  • Designed to meet IP65 or IP66 (although we do not have funds to subject it to certification).
  • Integrated flexible power options: 12v/24v automotive, solar (with integrated MPPT), and/or LiFePO4/LiIon/SLA battery (with integrated charge controller). It might also be possible to power with 5V USB – stay tuned.
  • microSD slot for Rhizome bulk data storage (replacing the previous energy consuming and unreliable USB memory-stick interface).
  • Slot for RFD900/RFD868 radio.
  • External UHF and Wi-Fi antennae for improved radio performance.
  • Mesh of Things/Internet of Things (MoT/IoT) interface with 2x opto-isolated digital inputs, and 60W load rated relay switched output. These sensor/controller interfaces will be MeshMS-controllable via future software-update.
  • 2x Internal ethernet ports (1x giga-bit and 1x 100Mbit). These are not routed to the outside of the IP65/66-designed enclosure, due to the cost that this would entail.
  • Option for USB charging port.
  • Internal USB port for future accessories.
  • Serial EEPROM in power/radio cable to allow control of radio regulatory parameters, without having to configure the Mesh Extender device itself.

Radio Regulatory Control

One of the significant challenges for the Mesh Extender, is that it must be easily importable during the acute phase of a disaster. Problems can easily arise when importing radio equipment in such circumstances, as the customs/border protection officers are typically very busy during such events. It must, therefore, be very easy for them to establish that the hardware conforms with local regulatory requirements.

To facilitate this, Mesh Extender hardware will only operate using Wi-Fi, unless the serial EEPROM in the power cable indicates otherwise. That is, it can be honestly said that a shipment of Mesh Extenders can transmit only in the 2.4GHz Wi-Fi band, if they are shipped separate from their power cables. This allows a single inventory, possibly regionally positioned, regardless of target country (subject to radio band compatibility, which will be discussed later). Kits of power cables, encoding the local regulatory parameters for each target country can then potentially be pre-positioned in-country ahead of time. Or failing this, such cables can be rapidly prepared using a special programmer, and then shipped either together with the Mesh Extenders, or in a separate consignment from the Mesh Extenders themselves.

A secondary use of the serial EEPROM is to inform the Mesh Extender whether it is allowed to accept unsigned firmware updates, or whether it is legally permissible to have arbitrary firmware installed. This is to address regulatory problems in places like the USA, where their national regulators are (unwisely in our view) moving towards such requirements.

See EEPROM memory layout for more information.

It should be noted that all tools required to program the serial EEPROM form part of the open-source source-code of the Mesh Extender system, and thus these measures go no further than necessary in preventing the kind of unintentional or accidental behaviours that national radio regulators typically require. That is, where there is a legitimate operational requirement to change the behaviour of the system, the tools required to do so exist – as indeed they exist for most programmable radio systems already approved for use in the relevant markets.

RFD900/RFD868 Radios

At present, the only difference in inventory is whether a Mesh Extender is physically fitted with an RFD900 or an RFD868 UHF packet radio. The RFD900 is suitable for transmitting from about 900MHz to 930MHz, and is thus suited for the Americas, Australia, New Zealand, many Pacific nations, and a handful of other countries. In contrast, the RFD868 is designed with the European/African 868MHz band in mind, and is thus suitable for those regions. Unfortunately, there is no single version of the radio that can operate in both bands, and ever were there such a version, it would require different antennae.

Thus, while it is possible to have regionally commonalised Mesh Extender hardware, there will still be two slightly different versions for the EU/African vs Americas/Oceania markets.

It should be noted that the RFD900/RFD868 radio module can be replaced inside a Mesh Extender by simply unplugging and replacing the radio module, so where there was an operational need to repurpose the radios between the differing regions, this could be done at reasonable cost.

Custom-Designed Injection Moulded Housing

Custom-Designed PCB

The PCB is currently undergoing the third revision to address outstanding errata. We hope to have samples before the end of March.

First revision PCB, front and rear:

First revision PCB, front and rear

Power/Utility Cable

We are engaging with Arkidelo to design and fabricate a low-pressure encapsulation mould for the D-SUB 25 connector, to provide appropriate environmental sealing of the cable head, from which the power input connector, battery connector and (optional) external USB charge ports will emerge. This will also need to include provision for the thumb-tighten screw-ins for the connector. The purchase order for Arkidelo to begin work is due to be raised on 03MAR17, and will take approximately 7 weeks before we receive the first parts.

For the power input / USB charge port connector, we are currently intending to use http://www.banggood.com/10Pairs-DC-MaleFemale-4PIN-24AWG-Waterproof-IP65-PVC-LED-Connectors-p-1073265.html?rmmds=search (AU$1.38 each, for IP65-rated 4-pin 1A connectors)

For the battery connector, we are currently intending to use the 3-pin version of the above (these are not mateable with the 4-pin ones) http://www.banggood.com/10Pairs-DC-MaleFemale-3PIN-22AWG-Waterproof-IP65-PVC-LED-Connectors-p-1073271.html?rmmds=search

We will also need IP65/66 rated D-SUB 25-pin female connectors, which we have yet to source.

Bill of Materials

Quality Control and Testing

We need to establish quality control, programming, test and qualification procedures for the Mesh Extender units. To be confirmed.

Mesh Extender PCB Test & Programming Rig

To be designed and implemented with Theo. Test rig that will allow flash programming and testing of all functions of the PCB.

  • Super-cap safe shutdown
  • Ethernet port 1
  • Ethernet port 2
  • Wi-Fi (access point)
  • Wi-Fi (ad-hoc)
  • Servald and LBARD operate
  • Internal UHF packet radio operation (sniff serial port?)
  • Internal UHF packet radio reads, honours and reports Power/Radio cable I2C EEPROM status
  • External radio operation
  • Relay-switched output
  • Opto-isolated inputs
  • microSD card bulk storage
  • Control of ssh login via microSD card special file
  • Control of ssh login via Power/Radio cable I2C EEPROM
  • Web-server operates
  • Web-server reports radio regulatory settings
  • Over-the-air update operates
  • Over-the-air update BID can be configured via microSD card special file
  • Over-the-air update BID can be configured in Power/Radio cable I2C EEPROM, and is honoured

Power/Radio Cable Test & Programming Rig

To be designed and implemented with Ryan. Largely based on our flash-rfd900 utility to probe and program cable, combined with functional indication through a set of LEDs.

Informal IP/Environmental Testing of Enclosures

Details to be confirmed.

Suggested tests:

  • Hot weather test (operation in full sun and high humidity to 45C).
  • Temperature and humidity cycling test.
  • Water spray test with Power/Radio cable connected.
  • Repeated sudden power-loss
  • … ?

Success criteria:

  • Uninterrupted operation through tests (confirm via pingability via Wi-Fi?).
  • System reboots cleanly.
  • No condensation or dust ingress at conclusion of testing.
  • … ?

Certifications

The ME2.0 has not yet been subjected to any certifications. We intend to pursue Australian/New Zealand, EU and US certifications of the electronics, and IP65 or IP66 certification of the hardware.

content/meshextender/2ng.1489716256.txt.gz · Last modified: 16/03/2017 19:04 by Paul Gardner-Stephen