Voltage 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.

Almost 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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Designing 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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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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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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A 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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When 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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My 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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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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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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