There are a number of ways to find out how much bandwidth is being used. This being the first pass at a digital to analogue conversion of the utilisation, I opted for simply using the uplink LED as an indication of the amount of traffic passing between my home and the internet.
This has some serious limitations. I do not know whether the hardware (broadcom chipset) or firmware (dd-wrt) contains the sampling algorythm that drives the LED, probably the chipset. Here's the first issue, an LED must be on for around 30mS for the human eye to register it properly. Networking packets are much much shorter than this. So the router must do a little math and translate real network traffic in to slower LED blinking. So there is a sampling loss, the LED is a rough approximation of the actual traffic.
Then, I must boost the 3.3V which drives the LED up to 14V required for the rev counter (most automotive dials and meters like this are linear 0-12 or 14V) For this I used a basic op-amp circuit. Without some swanky Digital to Analogue conversion I again loose a lot of resolution.
In the end, this is not a very good representation of the traffic bandwidth being used, but the further I got in to the project, the more it became an interesting object of art and less a solution to the original problem.
Note: I've been working with the guys from http://dd-wrt.com/dd-wrtv2/index.php
I highly recommend you upgrade your current software to this feature rich open source firmware.