Microphone Amplifiers

I’ve been prototyping microphone amplifiers for SmartMic. Although I’m not much on an analog guy I’m getting somewhere. Note the tiny SOT-23 op-amp soldered to a header!

We want to be able to handle electret and dynamic microphones, and have 0 to 40dB gain (trimmer adjustable). Here are the transistor and op-amp versions:

. . . → Read More: Microphone Amplifiers

Introducing the SM1000 Smart Mic

For the last few months Rick Barnich KA8BMA and I have been working on the SM1000, a embedded hardware product that allows you to run FreeDV without a PC. Just plug it into your SSB or FM radio, and you now have Digital Voice (DV). It’s based on a STM32F4 micro-controller, has a built . . . → Read More: Introducing the SM1000 Smart Mic

Scatter Plots and FreeDV

I’ve been prototyping parts of SmartMic (more on that later), for example the interface between the micro-controller and the radio microphone input. I have been using FreeDV as a test tool to evaluate the quality of the signals passing through my prototype circuits. As I worked I recalled a conversation with Mel Whitten. He . . . → Read More: Scatter Plots and FreeDV

Charging Strange Camera Batteries

I borrowed my Mother’s camera once, and somehow lost the special charger. So now every few months she brings it around and I have to work out how to charge the little Lithium battery. This usually involves fiddling with bits of wire, a current limited bench power supply (4V, 100mA), and a vice or . . . → Read More: Charging Strange Camera Batteries

My Vacuum Pump Won’t Stop!

The brake pump in my EV has been acting up. In an EV the brake pump provides vacuum to run the power brakes, as the original source of vacuum (the internal combustion engine) has been removed. I have mine connected to a little vacuum switch (bottom of photo with screwdriver adjustment) that turns the . . . → Read More: My Vacuum Pump Won’t Stop!

Natural and Gray Coding

After writing up the Variable Power Quantiser work I added another function to my fuzzy_gray.m Octave simulation to compare natural and Gray coded binary.

Here are some results for 3,4, and 5 bit quantisers over a range of errors:

Curiously, the natural binary results are a little better (about 1dB less Eb/No for the same SNR). Another . . . → Read More: Natural and Gray Coding

Variable Power Quantisation

A common task in speech coding is to take a real (floating point) number and quantise it to a fixed number of bits for sending over the channel. For Codec 2 a good example is the energy of the speech signal. This is sampled at a rate of 25Hz (once every 40ms) and quantised . . . → Read More: Variable Power Quantisation

Aspitech E-waste Recycling Tour

Yesterday Robert Hart was kind enough to take a group of local hackerspace members on a tour through Aspitech, and Adelaide e-waste recycler. The Australian government has mandated that all importers must pay to recycle 33% of their products (by weight), which has created a new, high growth industry. The South Australian government is . . . → Read More: Aspitech E-waste Recycling Tour

Not Activiating Mt Remarkable

Last Saturday I had my first Summits on The Air (SOTA) attempt on top of Mount Remarkable here in South Australia.

As a first step on Friday I registered my SOTA attempt on the Sotawatch web site

On Saturday morning I started by testing my FT-817 and Alexloop magnetic loop antenna at our camp. While . . . → Read More: Not Activiating Mt Remarkable

Fox Hunting

This weekend I have been attending the SERG Ham radio convention in Mount Gambier where I have enjoyed the company of some good friends and learnt a lot about fox hunting.

A group of us decided to go 3 weeks ago. The well-connected Mark VK5QI has been scouring Adelaide for fox hunting equipment, including beam mounts, . . . → Read More: Fox Hunting