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up: [[project:hgg|Project HGG]]

====== Project: HGG - Module Specification ======
[[http://shackspace.de/gallery/index.php/Projekte/HGG/groundstationmodules|{{http://shackspace.de/gallery/var/thumbs/Projekte/HGG/groundstationmodules.png}}]]

===== Time =====
  * I2C interface
  * Address: TBD

==== Feature Ideas ====
  * Support for multiple time sources via time-source accumulator module itself being a time source?
    * Stable master oscillator design (OCXO, Rubidium) 
  * I'd like to have room to have each module more than once, eg 2 timesource, 2 position sources, 2 receivers
  * Every module should have a type identifier and a serial number. Example: We have 3 groundstations tracking satellites and one uses dcf77 and one uses gps with a ublox gps module and one uses some other module or an internal clock. If we don't have the information about the measuring hardware in the samples, we can't know what we're trying to calculate. Thus it would be cool if every sample included information on the hardware that was used to sample it.

==== Questions ====
  * How to tell the module when we want to measure the time?
    * Beginning of I2C request message?
    * Interrupt?
  * absolute accuracy (required / possible) with 1pps GPS or DCF77

===== Position =====
  * I2C interface
  * Address: TBD

==== Questions ====
  * Is timing critical at all?
    * Probably not as long as the ground station is fixed 
    * For the time being only fixed ground stations will be supported
  * What absolute time precision is possible / required for the tasks?
    * 1pps GPS: 100 ns is easy, 1 ns is the limit. Ranging: 50m down to cm.
    * DCF77: signal edge can be measured with some ms error only due to narrow filters in the DCF receiver. Due to distance btw Mainflingen and receiver, there is a ms delay which changes with atmosphere condition (daytime, weather, multipath conditions). DCF is not suited for ranging purposes. OK for your wristwatch.

===== Measurement =====
TBD