Hardware Linksys Wrt54g
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UI VAST Linksys WRT-54G How-To

We use the Linksys WRT-54G routers to create our UI VAST WiFi Network. The capabilities of our routers have been heavily upgraded with various hardware and software modifications listed in the lower section of this page (eventually to be its own hardware modifications page).

If you are setting up a router in a vehicle or on the bus, there are a few things that you will need to have with you. They are listed below:

  • 1x Linksys WRT-54G Router
  • 1x Router Antenna Kit
    • 2x High Gain WiFi Antennas
    • 1x GPS Antenna
  • 1x Power Brick
  • 1x Power Inverter

To connect these items to the router correctly, please refer to the following image(s):

Be sure to put the antennas on the roof of your vehicle so they can work properly.

Upon power up you may need to toggle a switch on the side of the router to enable the battery-backup circuitry (not pictured). This ensures that the router can continue running even when your vehicle's battery voltage drops momentarily for events such as starting the engine.

Within a couple of minutes the GPS built into the router should get a lock and be ready to transmit its current position to other computers connected to the UI VAST WiFi network.

At the end of the mission, you will need to toggle the battery-backup circuitry off before disconnecting power from the router. This ensures our batteries stay in good condition and can power the router through extended periods of voltage fluctuations.

Linksys WRT-54G Modification Pages…

Hardware

Custom Hardware Modifications

Firmware / Special Settings/Configurations

Linksys (G, GS)

OpenWRT

OpenWRT VAST Edition

Mobile Networks Info

Overview of the "ui-rise" Ad-Hoc Network (RED/YELLOW/GREEN)

Battery Power System

The WRT-54G can be powered off of batteries to enable better positioning of the router. It also helps ensure constant data collection capabilities without the problems of being connected into overloaded inverters on the bus. It was thought that a small battery package could power the router during the whole trip, negating the need for inverter use.

The following data has been collected by Cliff from VAST's RED router with a factory power strip:

Start Up Measurements:

Run Voltage Amperage Power
1 14.40v 0.35 A 5.04 Watts
2 14.20v 0.38 A 5.40 Watts
3 14.44v 0.33 A 4.77 Watts
4 14.45v 0.33 A 4.77 Watts
5 14.46v 0.33 A 4.77 Watts
AVG 14.39v 0.34 A 4.95 Watts

Idle Measurements:

Run Voltage Amperage Power
1 14.00v 0.43 A 6.02 Watts
2 14.14v 0.41 A 5.80 Watts
3 14.10v 0.42 A 5.92 Watts
4 14.07v 0.42 A 5.91 Watts
5 14.06v 0.42 A 5.91 Watts
AVG 14.07v 0.42 A 5.91 Watts

Normal Usage Measurements:

Run Voltage Amperage Power
1 13.90v 0.42 A 5.84 Watts
2 14.08v 0.41 A 5.77 Watts
3 14.02v 0.42 A 5.89 Watts
4 13.98v 0.41 A 5.73 Watts
5 14.05v 0.42 A 5.90 Watts
AVG 14.01v 0.41 A 5.83 Watts

The maximum power consumption for the router seems to be around 5.91 Watts, or 6 Watts. This will be used as the design value for the battery power system. The design voltage for the system is going to be around 14.4volts. With this in mind, we can calculate a battery capacity in Amps (or Amp Hours/Hour) to power the system for any given time periods.

6 Watts / 14.4 Volts = 0.417 AH/H (= 417 mAH)

Since a mission generally lasts for 6 hours, we can use that as a design value for the system run time.

0.417 AH/H * 6 H = 2.502 AH (= 2502 mAH => 36 Watt Hours)

To get an idea of these values, we will compare this battery capacity requirement for our 14.4v system for a 6 hour flight against the battery capacities of various common battery cells that could make up this battery power system.

Battery Type Capacity (mAH) Voltage Cells Needed Cost Per Cell
Requirement 2502 mAH 14.4v … …
Alkaline AA* 2850 mAH* 1.5v 9-10* $2.0/ea
NiMH AA* 2100 mAH* 1.2v 12-13* $2.5/ea
Lithium-Ion 18650 2600 mAH 3.7v ~4 $5-$8/ea
  • We would need to look into higher capacity NiMH batteries to work for the whole time, but usually at these capacities the cell life is lower and we would need to replace cells more often. Alkaline batteries are non-rechargeable, and usually have lower capacity at certain discharge rates. It should still work though.

It would be nice to use Lithium-Ion batteries from a space perspective because it could require 1/3 of the cells of a AA solution. But fully charged these batteries would have a 4.2v open-circuit voltage per cell, putting the battery system at 16.8v.

We will need to review system requirements one more time before committing to a battery solution and purchasing the parts to build it. -Cliff

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