Retina Scan

Right-20140625@155858Left-20140625@155918More medical imaging. I present for your consideration the insides of my eyeballs. (Click thumbnails to view original full-size images.) The images shown were taken on Jun 25, 2014 using an Optomap wide-field retina scanner, probably the 200Dx model.

So now I have plausible deniability for anything that I'm alleged to have done on a system using retina scans for biometric authentication...

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Night Fury

toothlessArtist Mittie Paul created a wonderful interpretation of Toothless (from How to Train Your Dragon 2), inspired by traditional Viking art. You can get prints or merch featuring this image (at which, just look!).

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Magnetometer V: Fixed-Point Math

This is another article in my series about developing a magnetometer-based digital compass. Last time, I talked about estimating code size, and what I might do to fit the application in the roughly 5.25K program space available on an Adafruit Trinket.

In this article, I replace the floating-point math with fixed-point, and make various space-saving improvements to the calibration and rotation code. Read on for more.

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Medieval Manuscripts

MS20BXX-78vWe're kickin' it old-school on SGS today, with a lovely post on the British Library's Medieval Manuscripts Blog. The image to the right is from Royal MS 20 B XX. Click the image to see a larger version, or -- far better -- use the British Library MS Viewer to browse wonderful, high-res zoomable scans of the original.

Warning: All links above are more perilous Internet time-wasting rabbit-holes than Wikipedia and TVTropes combined.

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Magnetometer IV: Code Size

Last time, I presented a working proof-of-concept of a digital compass based on a three-axis magnetometer. That version was running in userland on a Raspberry Pi running Raspbian, which is a whole lot more computer than the Atmel ATtiny85 I eventually want to target. It was also coded for clarity rather than for speed or size.

In this post, I'll look at some quick-and-dirty ways to estimate program size for an AVR version (as well as some simple things we can do to save space). Read on for more.

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Magnetometer III: Working Prototype

In previous posts, I talked about a method of transforming magnetometer readings to compass headings, then experimented with using those transformations on real (but static) data. In this post, I'll present a working prototype of a vehicle compass using the methods I discussed earlier.
Read on for more details.
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Silverware Dragon

dragon-silverwareCheck out this dragon made of silverware, from Ohio artist Gary Hovey. (Long-time readers -- both of them! -- will noddingly remember the previous appearance of utensil-based dragon sculpture in these pages.)


Magnetometer II: Real Data

In a previous post, I speculated about a method of converting magnetometer readings to compass headings using affine transformations (specifically, three elemental rotations). In this followup, I'll gather some real data, then see how those transformations actually work in the real world. Read on for details.

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Magnetometer Reading to Compass Heading

I'm working on building a digital vehicle compass, using the Honeywell HMC5883L three-axis magnetometer as a sensor. Answering the question "Which compass direction am I facing?" from the raw sensor output data is somewhat more complicated that you might expect. This is especially true when using a microcontroller like the ATTiny85 with extremely limited memory. Read on for a discussion of the problems involved and my solutions. Read the rest of this entry »

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I2C with ATTiny85 on Adafruit Trinket

SONY DSCThe Trinket microcontroller from Adafruit Industries is a tiny and inexpensive (US$8 for a single unit) way to control your electronics projects. One of the coolest things about it is that you can do I²C (and communicate to lots of inexpensive sensors and displays using only two pins) and still have plenty of room left over for your code in the ~5.5KB of flash on board.

Read on to see an example of how to do I²C communication on the Trinket (or anything with an Atmel ATTiny85)  while shaving every possible byte. Also included: driving the Adafruit Mini 8x8 LED Matrix with I2C Backpack. Read the rest of this entry »

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