LightPi
Contents
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 too much 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.
*...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/collection (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.
Setup
Preparation
Hardware for the LightPi:
- 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
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)
Configuration
 |
| Raspberry Pi Model 3 B (left) and Model A+ (right), outfitted with a DS3231 RTC module (a third one on the bottm left). |
...
