LightPi

 

Introduction

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

 

 

Setup

Preparation

Hardware

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)

or:

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

 

Software

• The Raspbian image file from https://www.raspberrypi.org/downloads/raspbian/
• If you are using Windows: Win32DiskImager

 

LightPi zip archives

Always use the most recent version!

v20161115

File:LightPi v20161115.zip

First public version of LightPi.

Instructions inside.

 

Configuration

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

Details to follow --Nero2401 (talk) 03:10, 17 November 2016 (CET)

...