Rowetel

28,000 Electric km

By david, on November 20th, 2011

I haven’t written much about my EV for a while as nothing much has happened. It just goes and goes, and has just clocked over 28,000 electric km since it was converted. This post is a collection of notes from my EV driving in 2011.

It’s been two years since I installed Lithium batteries and . . . → Read More: 28,000 Electric km

Codec 2 at 1400 bits/s

By david, on November 15th, 2011

I’m in the process of releasing a 1400 bit/s version of Codec 2. Through efficient quantisation of the LSPs I have reduced the bit rate from 2500 to 1400 bit/s with only a small change in quality. This bit rate makes the codec very useful for digital voice over HF radio channels.

Here are . . . → Read More: Codec 2 at 1400 bits/s

My IP04 hacked and SIP ALG

By david, on October 23rd, 2011

Well this is a bit embarrasing. I make and sell embedded Asterisk boxes. My IP04 has been hacked! Some one made a bunch of calls to Guyana, among other places:

Call Summary

Destination
Calls
Amount

Algeria – Mobile Orascom
1
$0.39

Algeria – Mobile Wataniya
1
$0.59

Australia – 13/1300
2
$0.52

Australia – Adelaide
14
$1.82

Australia – Mobile
2
$3.18

Cape Verde – Mobile
1
$0.34

Cayman Is – Mobile C&W
1
$0.21

Dominica
1
$0.27

East Timor
1
$0.50

Guyana – Mobile
47
$16.91

Ireland – . . . → Read More: My IP04 hacked and SIP ALG

Driving the Nissan Leaf

By david, on September 2nd, 2011

Yesterday I took part in a Green Zone Drive event and had a test drive in the Nissan Leaf in the Mebourne CBD. I attended along with Michael and John, of the 3 Day EV fame. Also present were some other low emission vehicles and the Mitsubishi MIEV.

Our guide for the drive in the . . . → Read More: Driving the Nissan Leaf

Writing as Therapy

By david, on August 10th, 2011

It’s been a long time since I last blogged. I have been dealing with some big personal problems since March and haven’t had time for technical work or the will to blog on anything. I have however been doing a lot of private writing or journalling. So I would like to talk a little . . . → Read More: Writing as Therapy

Simple Low Pass Digital Filter Design

By david, on April 14th, 2011

For the $10 ATA DC-DC converter I need to design a low pass filter so that the discrete time model matches the real world DC-DC converter hardware. Given the time constant (tau), and the sampling rate Fs, I want to work out a value for c in the DC-DC converter discrete time model. In . . . → Read More: Simple Low Pass Digital Filter Design

Microwave Design and Why Experience Matters

By david, on April 4th, 2011

I recently helped out debugging the Wifi on another AR2317 router project. This is the same SoC chip as the Mesh Potato, so I was revisiting the same Wifi debug territory as 18 months ago.

Turns out this board had the same major bug as we found in the Mesh Potato – the reference clock crystal . . . → Read More: Microwave Design and Why Experience Matters

Resonant Feed Line Antenna for 40m

By david, on March 11th, 2011

After my success with the Flower Pot antenna on 2m I was inspired to try the same antenna design on the 40m (7MHz) Ham band. At HF frequencies, my ARRL handbook calls this design a Resonant FeeD line (RFD) antenna.

I used the dipole formula of antenna length equals 143/f meters where f is the . . . → Read More: Resonant Feed Line Antenna for 40m

$10 ATA Part 5 – Ringing a Phone with a DC-DC Converter

By david, on March 7th, 2011

In Part 4 I managed to get a micro-controller based DC-DC converter running. To ring a telephone we need a 20-50Hz sine wave of about 100Vpp superimposed on -48VDC. In other words a ring signal that moves between 0 and -100V.

The DC-DC converter set point can be programmed in software, for example -48V for . . . → Read More: $10 ATA Part 5 – Ringing a Phone with a DC-DC Converter

$10 ATA Part 4 – Building a DC-DC converter with a microcontroller

By david, on March 4th, 2011

For the $10 ATA I want to design a DC-DC converter using a micro-controller and a few discrete components. However, this means some sort of control system, i.e. a feedback loop that includes the “the plant” (the thing we want to control):

I admit I am intimidated by control system design. I studied this at . . . → Read More: $10 ATA Part 4 – Building a DC-DC converter with a microcontroller