Village DTN Router - Hardware User Interface

stephen.farrell@cs.tcd.ie, 2010-05-28

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This page describes the external user interface of the village DTN router box. That is: how to interpret the contents displayed on the screen and how to turn the device on and off safely.

The first thing to note is that users should only use the device as shown here - ONLY TRAINED STAFF SHOULD ATTEMPT OTHER ACTIONS, so please do not disturb cables, antennae or other external parts of the device. Any such tampering is likely to result in an non-functional village DTN router so please don't do it!

Village DTN router
Figure 1 shows a village DTN router deployed in Staloluokta in 2009.
(For all images on this page, you can click on the image for a full-sized version.)

Turning On and Off

The large switch at the side of the device is used to turn it on and off. The device requries approximately two minutes to fully boot and bring up all of the WiFi, mail and web services. PLEASE BE PATIENT - DO NOT CONSTANTLY SWITCH THE DEVICE ON AND OFF! Doing so could damage the device, in particular, the filesystems - such an error would be the equivalent of a hard-disk failure in a laptop.

switch
Figure 2: the ON/OFF switch in the "ON" position.

switch
Figure 3: the ON/OFF switch in the "OFF" position.

switch
Figure 4: a user switching the device to the "ON" position.

That's all nice and simple so far, but its gets a little more complicated when we need to understand how the device manages power, which is, of course, in short supply in Padjelanta!

Power Management

Basic Power States

As a solar-powered device, the village DTN router must manage its power so as to conserve battery in case there is not sufficient sunlight to charge the batteries. We have implemented a power management module for the village DTN router with the following features:

In each of the sleep or standby states, the device displays the time at which it is set to reboot, but note that after reboot, the device may go right back to sleep, if the power conditions warrant taking that action.

Override Mode

Whilst the device is sleeping, if a communications opportunity arises (e.g., a helicopter arrives), the device will not detect this since its radios are off, and we could lose the opportunity to send and receive data, which would be unfortunate, since such opportunities are relatively rare. However, a user who is present can turn the device on temporarily. The device will power itself up for 30 minutes, during which it will operate normally (if there is sufficient power), and then transit to whatever is the appropriate state, depending on the power conditions. This is the "OVERRIDE" mode of operation.

The device can be put into the OVERRIDE state at any time that it is sleeping.

To put the device into the OVERRIDE state, the user simply turns the switch to the "OFF" position, waits 5 seconds, and then turn the switch to the "ON" position. As usual it will take 2 minutes for the device to reboot, but it will then be in the OVERRIDE state and all WiFi, email and web services will be operational.

Summary of Power States

The table below summarises the different power states. Since the battery voltage level is displayed on the LCD screen we include the approximate voltage levels corresponding to each of the states. Voltage levels are somewhat technical, but provides the best way to measure the battery level, for the kind of battery we are using. The nominal voltage level when operating is 12V but in fact the levels fluctuate between 11.1V and approximately 13V depending on the state of the battery.

State Briefly Description Voltage Levels
UP Fully functional The device is operating normally as a WiFi access point, email and web server 11.6V and above
STANDBY-SHORT Sleep for 30 minutes The device is sleeping, to try charge the batteries. 11.4V to 11.6V
STANDBY-LONG Sleep for 3 hours The device is sleeping, to try charge the batteries. 11.1V to 11.4V
OFF Entirely powered off Either switched off manually, or else power is too low even for sleep 11.1V and below
OVERRIDE Work for 30 minutes The device will try operate fully for the next 30 minutes, if power permits N/A
SLEEP Sleep from 22:00 to 06:00 Just like everyone else, these nodes need to have a snooze at night N/A

LCD Screen

Village DTN router
Figure 5 - the LCD screen.

The device has small LCD screen inside the front window that provides some limited status information. Figure 6 (TBD) explains the various fields on the screen. Example messages are described below.

Note that the screeen is only ever updated once per minute.

Startup Screen
Welcome to N4C
Loading...

The startup screen is displayed about one minute after reboot (after the Linux operating system has booted). Between power on and this being displayed, one can see that the screen has power, but nothing is displayed.

UP State
V:1164 A:-376 14:03
UP

In the UP state, the device is fully operational and displays the state (lower left), the Voltage level (in millivolts) on the top left, the current being drawn in milli-Amps (as a negative number) or the current being received from the solar panels (positive numbers) in the top-middle, and the current local time on the top right. In this case, the battery level is 11.64V and the node is drawing 0.376 Amps from the battery.

OVERRIDE State
V:1164 A:-376 14:03
OVERRIDE Time:26min

The OVERRIDE state display is as for the UP state, but with the number of minutes remaining for the OVERRIDE state displayed in the bottom right.

STANDBY-SHORT State
V:1148 A:1513 14:03
STBYSHORT Wake@14:33

The STANDBY-SHORT state display is as for the UP state, but with the time scheduled for the next reboot displayed in the bottom right. In this case, the node is charging, receiving 1.512Amps.

SLEEP State
V:1164 A:-376 23:03
SLEEP Wake@06:00

The (overnight) SLEEP state display is as for the UP state, but with the time scheduled for the next reboot displayed in the bottom right.

Sample Error Screen
V:1189 A:-376 14:03
Voltage Spike

This screen is displayed in the case of a power management error where the voltage has changed too quickly to represent a reliable measurement. The error message may vary. Users should leave the device alone for at least 30 minutes if this is displayed. After that, if the device is not in one of the other known states, they should turn the device off, wait 10 seconds, then turn the device back on and leave it on, and report the problem (if possible).