This is an old revision of the document!
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.
The primary repository for the Mesh Extender is:
If you wish to develop on the individual packages, then these are the relevant repositories:
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.
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.
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:
This cable is a IP65 D-SUB 25 female to 3-pin and 4-pin IP67 cable, designed to connect the Mesh Extender to each of:
It also contains an integrated I2C EEPROM that tells the Mesh Extender which radio frequency and transmit power it is allowed to use, along with other configuration data.
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 has been raised, and will take approximately 7 weeks before we receive the first parts, probably early May.
See the bill of materials for details on the components.
See quality assurance for details on testing the cable, and programming the integrated I2C EEPROM.
We need to establish quality control, programming, test, qualification and certification procedures for the Mesh Extender units. To be confirmed.