Seb Holzapfel

Seb Holzapfel

Hobbyist | Student | Engineer

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Beginnings of a cheap 2-14GHz Mixer

Recently I've been working on a project for which I needed a 14GHz double-balanced mixer, however I'm on an extremely tight budget.

Luckily, most manufacturers provide free silicon samples these days, and Linear Tech (or rather, Analog Devices these days) is no exception. The LTC5548 is a pretty awesome MMIC, DC-6GHz IF, 1-12GHz LO, and 2-14GHz RF. It also includes a buffer so that you can use LO powers around the 0dBm mark instead of an ordinary mixer which might require.

Unfortunately, the evaluation board for the chip costs hundreds of dollars (~$300!) and I need multiple for my experiments.

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Analyzing the ugliest filter

Or perhaps 'How to make a microwave filter for $0'. Yesterday afternoon I wanted a 1.2GHz filter for an experiment, didn't need anything super-performant, and didn't want to spend any money. Before I actually show you what the filter looks like (because it's hilariously ugly), here's it's response (0-2GHz sweep):
Okay, the frequency response isn't so bad, but I'm putting -10dBm in so we've got about 10dB of insertion loss which isn't great. 300-600MHz seems to seep through at around -40dBc, which is surprisingly not bad. Here's the setup:
So you can see from the tuning scale that the

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Website update!

Alright; I've been sitting on the same old website theme for the last couple of years, so I figured it's about time to change...

Been sitting on this for a couple of weeks and slowly migrating all of my old content over. I think I've fixed most things now; so this new site's now live!

I've completely changed tech and moved over to the much sexier (in my opinion) Ghost blogging engine, with a heavily modified version of it's normal themes with some alterations to allow for my static content.

Annoyingly I couldn't import any of the comments from my

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BBB Scopeclock conversion - Part 1


A few weeks ago, I came across an article on Hackaday about memory mapped IO, and the sorts of toggle speeds you can achieve on the Beaglebone’s output pins when using this technique as opposed to just using the file access API. Around the same time, I was reading some articles on Pulse Density Modulation (as opposed to Pulse Width Modulation) for another project I was working on; in an attempt to increase the slew rate of a low-pass filter on the output of a microcontroller I was using.

As it happened, I’d had this old Dick Smith

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Uber Hexagon - An HTML5, Super Hexagon inspired seziure inducer.

Had a little extra time in-between half-yearly exams — so I had a crack at doing some canvas stuff in Javascript:


Code’s probably not perfect (web development has never really been my forte) – but I’m yet to find any serious bugs so no matter, it works :D — Only about 250 lines, too. Tested in Firefox and Chrome, supports iOS and android browsers too with touch. Not sure if it works in IE, heh.

Mechanics are similar to Super Hexagon’s, except the difficulty ramps indefinitely and there aren’t any patterns – the field is completely random. If anyone’s

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A terminal-based 3D model viewer

A natural extension on some of the javascript stuff I’ve worked on (Details on some of the 3D math is found there), I spent a short while piecing together a library and demo code that can render any standard .obj 3D model as ascii text; using mostly C++ and a little python.

I’m not sure exactly what a practical use of this would be, but I was thinking maybe along the lines of fancy console loading screens, viewing models on remote servers; etc.

This is a pretty visual project so I put together a little video demo:


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The UberDrive

Not so uber

The UberDrive (as I like to call it) is completely cross-OS USB-compliant storage device – and can store a whopping 7 kilobytes of data. Admittedly this was never really a ‘project’; more so a result of a couple of hours’ fiddling around. Basically, I worked off of the back of one of microchip’s CDC storage class demos, flipped the config switches so that it would run on my model PIC (24FJ64GB002)instead of what it was designed for and modified the device name. Then I dissected an old USB cable, breaking it out into headers so that

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