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The Lightrouter

Up to now, the Lightrouter was our preferred workhorse for collecting and transmitting Lightmeter data. It's low-cost and low-power design allowed for continuous nightsky measurements, automatic data transmission and even - to some extent -  remote maintenance.

But, over time several issues surfaced: 

  • The hardware version 2 of the WR1043ND rendered our firmware image obsolete, leading to a more manual setup routine.
  • Future hardware versions will come with a locked firmware, preventing the use of OpenWRT (due to a new FCC rule).
  • In offline-scenarios (no NTP, and no GPS) the internal clock performed terrible, exhibiting nonlinear, irregular drifts.
  • The internal flash memory is not large enough to hold the entire setup, leading to the need of an overlay filesystem, creating a high dependency on the presence of the USB stick.
  • Due to ill-defined brown-out behaviour of the router, the filesystem of several USB sticks got corrupted, leaving the stations paralyzed.
  • Our central server died (summer 2016), leaving the reverse-SSH-tunnels dangling in mid-air, and thus preventing remote connections and data collection.
  • Power consumption with up to 18W is quite high for solar powered off-grid stations.
  • Some gerneral reliability issues.

The LightPi

To combat all these shortcomings, the LightPi is under development. Based on a Raspberry Pi, extended by a realtime module, the LightPi will be easier to set up and to maintain, without increasing the price tag.

Some of it's main features are:

  • High and reliable hardware availability, good inter-generation compatibility.
  • Higher computing power and full debian-based operating system.
  • Lower power consumption (2-4W [Model 3 B], 0.5-1.2W [Model A+]). * 
  • 4 USB ports (Model B+ upwards), eliminating the USB hub.
  • SD-card instead of small onboard flash - no more overlay filesystems.
  • Highly accurate DS3231 RTC module (+/-3.5ppm).
  • Simple plug-and-play with any FAT32 formatted USB stick for data storage.
  • As inexpensive as the Lightrouter.
  • Uses A. Trawöger's Lightrouter-"lightmetermini"-python-driver.

*...based on interpolation of various internet sources.


As the LightPi platform ist still under active development, several features are not yet implemented:

  • Remote shell access (partly implemented).
  • Data transmission (planned).
  • NTP synchronsiation (planned).
  • GPS synchronisation (planned).
  • On-site network service for data access (planned).
  • Independence of a central server infrastructure (design guideline).


Current state

The LightPi project's current state is  developing / testing .

All the key networking capabilities have yet to be implemented, but the offline version is already up and running. First long-term reliability tests are currently in their starting phase.

Hardware acquisition

LightPi shopping list

  • Raspberry Pi (any model)
  • DS3231 RTC module
  • MicroSD / SD card (dep. on RasPi model) with 4+GB
  • Power supply (5V, micro USB)
  • USB stick (FAT32 formatted)
  • For model A/A+/Zero USB hub
  • For model Zero: USB-OTG adapter
  • Optional, but recommended: A case for the RasPi


Finding a source for the Raspberry Pis should not be difficult, as big electronics resellers (e.g. RS Components) have them listed. Usually the A/A+ models (and their cases) are harder to find, and the Zeros tend to be outsold.

A suitable RTC module can be found here: [1]

Choosing a Raspberry Pi model

Some hints regarding the different models:
  • All "B" models have 2+ USB ports, eliminating the need for an USB hub.
  • Also, all "B" models come with an Ethernet port, the A/A+/Zero models do not have native networking capabilities.
  • Model 3 B even has it's own onboard WiFi adapter.
  • The Models A+/Zero have the lowest power consumption - ideal for off-grid stations.
  • Model Zero has no fullsized USB port, thus needing an USB-OTG adapter.
  • First generation RasPis (1A and 1B, or just "A" and "B") use full size SD cards, other models use MicroSD.
  • Used first/second generation RasPis can be found very cheap on the internet.
The bottomline is:
  • Minimum energy consumption: A+/Zero
  • Maximum networking capability:  3B





For the setup process you need:

  • Your computer
  • SD/MicroSD card reader
  • HDMI capable monitor
  • HDMI cable
  • USB mouse
  • USB keyboard

(The USB/HDMI items may be borrowed from your computer - no need for a second set.)


Optional, but highly recommended for the setup process:

  • Internet connection via WiFi
  • USB WiFi adapter (for all models except 3 B)


  • Internet connection via Ethernet
  • USB Ethernet adapter (for models A/A+/Zero)





Always use the most recent version!

Version v20170810



  • Semi-graphical installer, minimizing the need for command line acrobatics
  • Data zipper, moving last months data to a zip archive, greatly reducing disk space consumption
  • Google drive uploader, copying completed month-archives to your cloud space
  • Heartbeat files, uploaded to your google drive, providing a quick glance at the stations health

Further instructions inside.

Version v20161115


First public version of LightPi.

Instructions inside.



LightPi RTC-Module.jpg
Raspberry Pi Model 3 B (left) and
Model A+ (right), outfitted with a
DS3231 RTC module (a third one
on the bottom right).

Contact and contribution

You are alway welcome to test and give feedback. The easiest way to communicate is to just edit the buletin board section below.

--Nero2401 (talk) 14:02, 10 August 2017 (CEST)

Bulletin board