Microservers

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Gen 3.2

Gen 3.1

Microcontroller-related

Other Microserver-Related


Introduction

Microservers are low-power computers usually located at a field site in support of data acquisition. We devoted some time and effort into designing and building a microserver for SEAMONSTER with general capabilities that could be used elsewhere, beyond Southeast Alaska. The driving idea was to facilitate geophysical data acquisition in harsh environments by means of a general-purpose field computer, to help get researchers out of the electronics lab and into the field, and to get those researchers more and better data per research budget dollar. The Vexcel Microservers page is the gateway to specifics of design and functionality.

Microservers can be backbone components for a sensor web and in terms of three "component characteristics": Data, communication, and power management. Henceforth we take as implicit the fourth characteristic of survivability (sometimes also 'ruggedization').

Data

The Microserver has Analog, USB, PC/104, Serial Port, and Ethernet. Data is stored in a solid state flash drive, so capacity > 16 GB is feasible. The unit has an internal L1CP GPS board capable of reaching decimeter-scale location precision. Earlier versions of the Microserver included a 4khz ADC for sampling up to four seismic sensors, typically geophones. Other data sources we've integrated include webcams, met stations, pressure transducers for measuring water depth, and a gateway for a mote-based sensor network.


All of this serves to illustrate the Microserver potential to acquire and store data for later retrieval. What did not come out of the 2002--2009 projet is a single simple high-level interface tool that makes data source integration simple. At this point it is difficult work, particularly to go from something that works in the lab to something that works reliably in the field.


Communication

Communication rates of 100 kbps with a 5% duty cycle are adequate for all but the most data-intensive applications. Microservers initially worked in ad hoc network mode using the 802.11G protocol and an internal Ethernet bridge, an off-the-shelf unit from LinkSys. This was subsequently abandoned in favor of an Ethernet router -- also from LinkSys -- which had more robust behavior. The 802.11G carrier frequency is 2.4GHz and an enclosure-internal 1/4 watt amplifier serves to give decent range (> 10 km) under good conditions, with data rates as high as 5 Mbps. However the WiFi communication problem is far from solved. A design revision would probably switch to a more robust 900 MHz radio modem.


Power Management

This is the strategy we adopted

  • Create a power conditioning system (PCS) custom circuit board--including a microcontroller (uc)--that operates for 3 years on internal batteries. (Done.)
  • Configure the microserver to receive operational power from an second external power supply, 12 volts DC. (Done.)
  • Include a recharge input (typically from a photovoltaic source) that can recharge the external supply. (Done.)
  • Integrate a low-power Single Board Computer (SBC). (Done.)
  • Create a software control structure to minimize the power consumption of the SBC. (Incomplete.)
  • Define a communication protocol between the SBC and the PCS-uc. (Done.)
    • SBC (user-designed processes) can turn other system components on and off
    • SBC can request system sleeps for minutes / hours / days
    • SBC can request system external supply voltage reading.
    • PCS can force a system sleep if voltage drops below a threshold
  • Instantiate hang-resistant failsafes in the PCS-uc firmware (Done.)
  • Instantiate complementary failsafes in the SBC. (Done.)
  • On top of all this: Build a task manager on the SBC. (Done.)


Field Testing

We have field tested microservers with the notable success that the flagship unit has overwintered near the terminus of Mendenhall Glacier twice.