Don't Panic, it's a Serval Mesh Extender

I have been working on the firmware for the Mesh Extenders the last couple of weeks.

This has involved combining a few features to make a 0.01 release that can go out on the perk Mesh Extenders, as well as some WR703N-based mesh extenders we are preparing for a monastery (more on that in a later post).

I wanted the firmware to support updating of the servald binary and config file, as well as preventing login as root in normal operation, and operating a captive portal so that people connecting to a mesh extender get some idea of what is going on. It also needs to support the different hardware types we are using.

This is all finally coming together as the following image shows.   The captive portal automatically pops up on my Mac if I associate with a mesh extender by Wi-Fi.

I'll talk more about the firmware structure later, and document it on the wiki.  Anyone wanting to take an early look can checkout the source code and look in the somewhat erroneously named mr3020 directory.

But for now, I am happy that we have the main functions of the mesh extender firmware functioning.

Open-Source Collapsable Communications Tower

[Update: the design files to make your own tower are now available via this post.]

I have been helping some mechanical engineering students from the side-lines with a project to make an open-source rapidly-erectable communications tower, with internal space for comms gear and batteries.

I hadn't caught up with them for a few months, but today was student expo for the department, and so I went down to see what they had created.

It was very pleasing to see a nice that they had indeed managed to make a 6m high tower that can be assembled in less than 10 minutes, and consists entirely of common hardware and a few 3D printable parts, as you can see below:

And again with one of the students who designed it for scale:

The design uses three guy ropes for stabilisation, and was designed to accept an 85m/s static wind load.  The practical limit would be less than that under realistic dynamic wind conditions.

Following my suggestion, the entire tower when broken down is small (<140cm total linear dimensions, approximately 1m in longest direction) and light enough (19kg) that it can be included in checked luggage on a normal commercial flight.

By using only common plumbing components and a few 3D printed components, it could in principle be manufactured (or repaired) in relatively infrastructure deprived settings, provided you had a 3D printer, of course.

Think you'll have trouble finding 3D printer filament?  Then you might want to make use of one of the other student's projects, turning plastic milk bottles into 3D printer filament.  That project has a bit more work to do, but the general concept is there and working.  There are also some other projects around the world working on the same kind of resource scavenging approach.

Serval recognised in International Red Cross/Crescent World Disasters Report

It is very pleasing to see our partnership with New Zealand Red Cross to enable communications during disasters has been recognised in the International Federation of the Red Cross/Crescent (IFRC) World Disasters Report.

"This collaboration between the New Zealand Red Cross, DeLorme and Serval has created a communications system with many benefits from the complementary capabilities of the three technologies, including the smarts and sensors of the smartphone; the global reach of Iridium; resilient communications due to path diversity and the store and forward mechanism; the value for money of commercial off-the-shelf components; and a familiar interface that can be used before, during and after the disaster."

The full report can be downloaded here:

http://www.ifrc.org/PageFiles/134658/WDR%202013%20complete.pdf

Improved 3D printable case for mesh extender

In recent blog posts I have been talking about the 3D printable cases for the mesh extender prototypes.  We had a little problem with the first prototype not fitting the USB memory sticks that we had, so Musti kindly tweaked the design to make more room, as can be seen in this shot:

 With the lid on it looks like this:

The ABS plastic just has a nicer finish than the other plastic we used on the first test unit.  With this change it is just about right, except that it ended up bring a little too short for some reason, perhaps an issue with our 3D printer, as you can see by the little gap behind the lid here:

We will just print the case 1mm longer, and all should be well.

The next step from here is to adapt it for the MR3040 router which has a small rechargeable battery, and means that we can have a single-piece Mesh Extender with at least a few hours of battery life before adding an external battery.

Mesh Extender custom case fitting

As mentioned in the last post we now have a 3D printable case for the MR3020-based Mesh Extender prototypes.  Until today we had only seen the images of the one that Musti printed in Slovenia.  But now thanks to the technical staff here in the department, we got one printed up this morning while I was teaching to see how it looks, and if it fit the components we were using here.

First, here is the unit after we put all the parts in, in fashionable Flourescent Yellow, almost verging on the appropriate International Standard Yellow-Green:

We did, however, hit a little snag: The USB memory sticks we are using here, while very small, are slightly larger than the ones that Musti was measuring against.  Similarly, the USB connector itself had a taller flange than anticipated.  The end result was the case is about 2.5mm too narrow, and about 1mm to low around the USB connector:

This we remedied with a bit of filing to make a slot to accept the USB memory stick until we can tweak the design.  I filed off some of the stylistic curves on the memory stick as well to make this easier.  Then it all fit:

Musti has done a great job making it all slot together, and feel really firm and stable in terms of the positions of the components.

Now to build an updated servald binary including all our recent changes and bug fixes...

Custom case for MR3020 based Mesh Extender prototypes

With the help of the very capable Musti from WLAN Slovenija and some of our crowd funding campaign funds (thank you again to everyone who contributed!) we now have a nice 3D-printable case for the MR3020-based Mesh Extender prototypes.

The following images are supplied by Musti, as we are yet to print some of these out ourselves in the lab.  You can be sure we will be doing this as soon as possible next week.

Having our own case is one of those little things that makes a big difference to the end usability, and also feasibility of manufacturing these units in small quantities.  No odd parts poking out. No lids that won't close properly. All little things that make a big difference.

Musti has made the case so that the PCB and radio just slide in, and with a little extra PCB all the connections can be made without having to solder anything -- a very nice time-saving trick.

We will be putting the CAD files up on http://developer.servalproject.org/wiki as soon as we get the chance.

Next we are looking at doing the same for the MR3040, which is much the same as the MR3020, but has an internal rechargeable battery -- that would give us a one-piece complete Mesh Extender, which is very appealing. Also, the MR3040 is much easier to open to get the PCB out in the first place compared with the MR3020 whose lid is cemented and clipped shut, and generally Un-Fun to open by the dozen.

Arduino Yun as a possible Mesh Extender Platform

Regular readers of this blog will know that we have been looking at a variety of hardware options for the Serval Mesh Extender.

The Serval Mesh Extender is a device that combines ad-hoc WiFi meshing with long-range license-free UHF packet radio to allow the easy formation of mesh networks spanning useful distances. Typically the UHF packet radio has a range about ten times greater than WiFi. This means that in ordinary suburban and urban areas we get a range of a block or two, and in open rural areas the range can be in the kilometres.

We run our award winning Serval Mesh software over the top, providing an easy to use communications system that lets you use your cell phone without cellular coverage, for example, during a disaster, or when you and your friends are near one another outside of the range of your native network. For example, if you are at an international gathering and don't want to pay $4 a minute for the privilege of calling someone a few hundred metres away.

The challenge with the Mesh Extender design is that we haven't had the budget to design our own device from the ground up. As a result we have been using existing hardware platforms, and trying to adapt them to accept the excellent RFD900 UHF packet radios we source from RFDesign (their link margin is probably about 10dB better than competing radios that we are aware of).

This means that we have been doing things like modifying TP-LINK MR3020 wireless routers to build prototypes. While it works, the process is far from satisfactory, and the physical steps take a couple of hours per unit, which makes the effective unit price very high, despite the low cost of the MR3020 unit itself.

This is where the Arduino Yun is very exciting for us. It has all of the functionality of the MR3020 in the form of the mesh-friendly Atheros processor and WiFi system-on-a-chip running Linux, and of course being an Arduino it has plenty of connectivity options for us to connect to the RFD900, which just uses RS232 serial. As an added bonus the Yun has a microsd slot, so we don't need to use a USB memory stick for mass storage, which actually makes a noticable impact on power consumption. The larger flash on the Yun is also welcome, as the 4MB flash on the MR3020 is, frankly, a pain to work with.

While we are still working on the integration, the prospect is there for the Yun to save us a lot of time, and hence cost, in making future prototypes, and the Yun board itself could be the basis for a customised PCB that exactly meets our needs, and allows us to just plug the radio module directly onto the PCB.  Here you can see the Yun connected to an RFD900 radio ready for integration testing:

In short, the Yun is opening a new opportunity for us to innovate faster, more affordably, and with a better result.