The Serval Mesh Extender can best be described 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,” Paul Gardner-Stephen, founder of the Serval Project, explained in a guest blog post published on the official Arduino blog.
“We run our 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. [Or], 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, says Gardner-Stephen, is that the Serval crew hasn’t had the budget to design its own device from the ground up. As such, the team has been using existing hardware platforms, all while trying to adapt them to accept RFD900 UHF packet radios they sourced from RFDesign.
“This means that we have been doing things like modifying TP-LINK MR3020 wireless routers to build prototypes,” Gardner-Stephen continued. “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.”
Enter the Atmel-powered Arduino Yún, which, as the Serval Project founder points out, offers all of the functionality of the MR3020 in the form of the mesh-friendly Atheros processor and WiFi system-on-a-chip running Linux.
“Being an Arduino it has plenty of connectivity options for us to connect to the RFD900, which just uses RS232 serial,” he explained. “As an added bonus the Yún has a microSD slot, so we don’t need to use a USB memory stick for mass storage, which actually makes a noticeable impact on power consumption. The larger flash on the Yún is also welcome.”
Gardner-Stephen says that while his team is is still working on the integration process, the “prospect is there” for the Yún to save a lot of time and cost in terms of helping to design future prototypes.
“[Of course] the Yún board itself could be the basis for a customized PCB that exactly meets our needs and allows us to just plug the radio module directly onto the PCB,” Gardner-Stephen concluded. “In short, the Yún is opening a new opportunity for us to innovate faster, more affordably, and with a better result.”
As previously discussed on Bits & Pieces, the Yún – designed in collaboration with Dog Hunter – is based on Atmel’s ATMega32u4 microcontroller (MCU) and also features the Atheros AR9331, an SoC running Linino, a customized version of OpenWRT. The Yún is somewhat unique in the Arduino lineup, as it boasts a lightweight Linux distribution to complement the traditional microcontroller (MCU) interface.
The Atmel-powered Arduino Yún can be snapped up for $69, or €52.