Digit Span Test (Online Tool)

The digit span test is a way of measuring the storage capacity of a person’s working memory: A testperson is visually or auditorily exposed to a sequence of digits one after the other. Right afterwards, the test subject has to recall the correct digits in the same order. Most people manage to recap around seven digits. I have written an online tool that lets the user determine their digit span test score. It is available at the website tools.timodenk.com/digit-span-test. Continue reading Digit Span Test (Online Tool)

Cubic Spline Interpolation

Cubic spline interpolation is a mathematical method commonly used to construct new points within the boundaries of a set of known points. These new points are function values of an interpolation function (referred to as spline), which itself consists of multiple cubic piecewise polynomials. This article explains how the computation works mathematically.

After an introduction, it defines the properties of a cubic spline, then it lists different boundary conditions (including visualizations), and provides a sample calculation. Furthermore, it acts as a reference for the mathematical background of the cubic spline interpolation tool on tools.timodenk.com which is introduced at the end of the article. Continue reading Cubic Spline Interpolation

Commute Time Tracking

According to the U.S. Census Bureau the average commute time for U.S. citizens who are neither working at home, nor walking or biking to work, is 25.9 minutes. My commute time from Karlsruhe to SAP is usually about 38 minutes one-way; often protracted by traffic jams. However, these can be avoided by departing at times where rush-hour traffic has not fully built up yet. But which departure time works best? Is it 07:00 or rather 09:00? When departing at 07:40 how much time could one save by departing just ten minutes earlier? In addition to the traffic conditions on the outbound trip, the delay on the way back has to be taken into account likewise. With about 9 hours and 20 minutes spent at work, the traffic at 16:20 matters for a departure at 07:00. For a 09:00 departure it would be 18:20. Continue reading Commute Time Tracking

Observing the ISS from Earth

The International Space Station is orbiting our planet since 1998. One orbit takes only approximately 92 minutes and the ISS is sometimes visible at the night-sky. To the naked eye it looks like a bright star crossing the night sky in just a few minutes.

In April 2017 I was visiting my uncle in Almeria, Spain. He has a nice telescope and we were wondering, whether it would be possible to recognize the International Space Station’s shape through the telescope. As it turned out it is possible but not easy: The primary difficulty was to keep the rapidly moving ISS within the telescope’s field of view. Additionally, the video output was very shaky, which made comprehensive post-processing necessary. Continue reading Observing the ISS from Earth

Port Manipulation and Arduino’s digitalWrite Performance

The widely used Arduino IDE offers many easy-to-use functions, one of them is  void digitalWrite(uint8_t pin, uint8_t val) . It sets one of the microcontroller’s pins to either high or low and serves well in many cases. However, it has a really poor performance, i.e. execution time. This post analyses both, speed and interior of the digitalWrite function, and proposes alternative, high performance solutions for setting output pins.
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Arduino 433 MHz Wireless Module

433 MHz Wireless Module
The 433 MHz wireless module. Transmitter: top-left. Receiver: bottom-right.

This post provides a quick reference for the 433 MHz wireless module, which is widely used in combination with the Arduino. The VirtualWire library is one possible way of utilizing the module. Continue reading Arduino 433 MHz Wireless Module

Smart Home Security Camera

This post explains the technical background of the security camera system, shown in the following movie. The post will answer the questions: How to detect a thief, how to take a photo, how to get notifications on your phone, and whether the system would work in reality.
Continue reading Smart Home Security Camera