This page describes how to build an inexpensive
power-over-ethernet outdoor WiFi access point/bridge using the Buffalo WHR-G125
wireless router. Normally these routers sell for about $45, but they've been known to go on sale for as little as $25, which makes them attractive for modification. The cost of all of the additional parts used in this modification came to about $30, so it's quite possible to build an entire outdoor AP for well under $100 total.
The router is loaded with third-party DD-WRT firmware, which allows it to be used not only as an access point, but also as a client bridge or a wireless distribution system (WDS) node. These options allow you to create an outdoor wireless bridge between buildings. The network inside of each building can be wired or wireless. See this page for instructions on installing DD-WRT on the WHR-G125.
A power-over-ethernet modification makes installation easier by requiring only one Cat5 cable to be run to the box.
A biquad antenna was added to give some gain and directivity, although this may not be desirable in some applications.
If you don't want to build your own outdoor access point, there are some fairly inexpensive alternatives on the market from EnGenius and Meraki, although neither is "open" hardware that supports third-party firmware.
The antenna I used was a homemade biquad similar to many others highlighted on the web. I won’t go into construction details since many other people already have very good instructions. Here are a few examples:
The WHR-G125 comes with a single non-removable external antenna. A second internal antenna is etched onto the printed circuit board. In order to use the biquad antenna, the external antenna was removed. To do this, the coaxial cable running from the printed circuit board to the antenna was desoldered from the circuit board. The RG-174 cable running from my homemade biquad antenna was soldered in its place.
Factory Router PCB
Closeup Showing Factory Antenna Connection
Biquad Antenna Connection to PCB
Providing power over Ethernet to the WHR-G125 is a little tricker than with most other consumer-grade routers. The “wall wart” power supplies of most routers provides a loosely-regulated 12VDC to the router, which then uses an internal voltage regulator to drop the voltage down to the 5V or 3.3V that the electronics need. Apparently Buffalo was found a way to cut some cost, however, by using a “wall-wart” that supplies a regulated 3.3V to the router. While it may be possible to provide 3.3V over Ethernet over short distances, a long cable run will result in a voltage drop that will bring the voltage seen at the router down below its operational level. Here’s a power over Ethernet calculator you can play with to get a feel for how voltage drop affects things:
To get around this problem, I decided to build a simple 3.3V linear regulator into the router. I could then feed a higher voltage to the router over Ethernet, which would mitigate the voltage drop issue. While this isn’t the most energy-efficient solution in the world, it works. So I use a 10V “wall wart” transformer to feed the router box, and the regulator steps that voltage down to 3.3V for the router.
Voltage Regulator Schematic
To inject power into the Ethernet cable, I used an RJ-45 coupler designed to connect two Ethernet cables together. After opening the coupler housing, the PCB traces that were to be used for the DC power were cut, and the power wires soldered to the “router” side of the traces. In this way, DC power is provided to the router, but not to the other side of the coupler where the WAN is connected.
RJ-45 Coupler Modified for use as Power Injector
Finished POE Injector with "Wall Wart" Power Supply
A visit to Lowes produced a perfectly sized (6"x6"x4") sealed PVC box for about $11 (Item Number 10030) . Because I didn’t want to drill any more holes than necessary into this enclosure, I used epoxy to fasten standoffs to the enclosure for PCB mounting. A single hole is drilled in the enclosure for the Cat5 cable. This hole is sealed with a sealed feedthrough and silicon.
Standoff Epoxied to Enclosure
Two extra holes were drilled in the WHR-G125 circuit board for mounting, and three holes were drilled in the biquad reflector for mounting. The voltage regulator circuit is epoxied to the WHR-G125 board. The WHR-G125 board is mounted to three metal standoffs that are epoxied to the enclosure, and the biquad antenna is mounted on three 1.75” nylon standoffs above the WHR-G125. board.
Voltage Regulator Circuit Epoxied to Router PCB
Router PCB Mounted in Enclosure
Finished AP with Cover Removed Showing Antenna Mounting
The Lowes enclosure has four tabs with mounting holes. A few pieces of scrap metal and two U-bolts provide an easy pole-mounting platform.
Mounting Hardware and Feedthrough on Bottom
Finished Product Ready for Mounting
Here is a rough breakdown of parts cost:
Buffalo WHR-G125 - $45 (sometimes as low as $25)
U-bolts - $1.25 each
Wall Transformer - $4.25
Dual RJ-45 Jack - $2.50 each
Voltage Regulator Circuit - $2.00
Feedthrough - $1.50
Standoffs - $.50
PC Board (used in Biquad) - $2.00
Coax - $.50