Log a quick overview of the latest changes, for your convinience
Projects finished projects, both hard and software
Ideas / How-tos Short articles about technologies, unfinished ideas and other information not related to a specific project
Tidbits Small things, no programming or electronic knowledge required
About about me and this website
11.8.2014

Watching all the movies ever made

A stack of DVDs on a tableHow long would it take to watch all the movies ever made?

This question popped up a few times over the last few months, so I decided to do a bit of data mining and math.

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20.7.2014

Taking some pain out of voltage dividers

3 resistors which have been split open in the middle on a wooden boardVoltage dividers are a common circuit to interface high(er) voltage signals to lower voltage interfaces. For some reduction factors like 1:2 it is fairly easy to find the right resistor combination. However the common resistor values are arranged in a rather ingenious way, which can make it difficult to calculate the correct pair for any given reduction factor.

To make this task a bit easier, I wrote a small online tool.

3.7.2014

With a fistful of transistors 1 – Back to the basics

A schematic of a transistor based AND gateAlmost everything a CPU can do can be reduced to some sort of logic equation. In math and theoretical computer science the most common logic operations are AND, OR and NOT. From an electrical point of view NOR and NAND gates are far more popular.

In theory every logic operation can be performed using only NAND gates. In practice it is more useful to use other gates as well. This post will describe how the different gates can be implemented using transistors and why, for my purposes, NAND and NOR are preferable over AND and OR.

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3.7.2014

With a fistful of transistors – Building a CPU from scratch

A collection of sot23-3 transistors in a dirty palmDesigning a processor is a common topic during a computer science education. But unless you specialize in computer architecture, you rarely end up building the actual hardware. Even if you do build it, most classes tend to use FPGAs or at least some ready-made hardware parts.

Just for fun, I’ve decided to build my own processor just from basic components.

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2.3.2014

A simple simplex UART for debugging AVRs

If you don’t have any way to output information, debugging projects can get annoying very quickly. Often you can help yourself by blinking LEDs but one of the most popular method still is “printf-debugging”.

Since I tend to slim down my projects as much as possible, I often end up with microcontrollers without built-in serial communications. There are a few software UART libraries around, but those are normally fully featured implementations and need timers or interrupts.

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27.7.2013

PCB sample set

sample set

Circuit boards come in all shapes, sizes and colors. There are many reasons why you might want to swap the standard green boards for something more exciting. It might be to simply make your projects stand out more.

Dangerous prototypes are quickly identified by their bright red color, genuine Arduinos are always blue and the Lilypad is a lovely lilac.

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22.5.2013

AVR programming cable

ISP programming cableA while back, I made a very small AVR programmer, based on [simpleavr]s vusbtiny programmer. Even while I was working on that board, I became annoyed with the fact that more than half of the board was taken up by the USB and ISP connectors.

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12.5.2013

Cloth laptop holder

Cloth laptop holderWhen I couldn’t figure out a way to add a monitor to my kitchen, I designed a simple little laptop holder to hang on the kitchen door.

On one side it has two pockets, one on the front, which fits the lower half of my laptop snuggly. The other pocket is on the back. Originally I planned to fit a wooden board in there, to stabilize the holder and keep it from tipping forward. However this doesn’t seem to be necessary, so now it serves as place to store printed out receipts.

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12.5.2013

Hardware mute button for laptops

Hardware mute buttonMy third biggest fear in life is having my laptop play a loud startup sound in a quiet library or crowded lecture hall. It comes right behind my fear of moray eels and small pebbles.

To address this serious problem, I made a small hardware mute button for my keychain.

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8.4.2013

Simple silkscreen reference board

Silkscreen test board

The last step in my PCB design process normally is the silkscreen. When I try to design a nice helpful silkscreen, I often find my self wondering “How small can I make the text?” or “If I put this text over a via, will it still be readable?”. Usually I end up digging around some old designs to find some examples of what worked, and what didn’t.  But during my last run, I got a bit annoyed and decided to include a small reference board for the most  common situations.

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23.3.2013

Using internal pull-ups to read tri-state inputs

Schematic for ternary input

Sometimes you just need one more input button or switch.

There are many different ways to use you existing pins more efficiently. If you still have a free analog pin, you could use a resistor ladder to connect multiple buttons to one pin. Or you could use a key matrix to drastically cut you pin count for many buttons. However, if you only need one or two additional pins, here is a neat way to connect 1.5 buttons per input pin.

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12.1.2012

Minimalist AVR programmer

The tiny isp board between a standard 6 pin ribbon cable and an USB extension socket

I always like a challenge, so when I saw [simpleavr]s vusbtiny programmer, I started to wonder how small I could make an AVR programmer. All in all I’m pretty pleased with the result.

The schematic is almost the same as the original one. I’ve only added a LED and a resistor to indicate a proper power supply.

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1.1.2012

Measuring rotor speed with an open bench logic sniffer

Our little 'copter

Recently we suspected that one motor of our hexacopter had been damaged in a crash. Since removing the motor requires almost the complete disassembly of the copter I started thinking of ways to test the motor in place.

The most important parameters I was looking for were the speed of each rotor relative to the others, and the consistency of the speed over several rotations.

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