Apache Cassandra™ is a massively scalable open source NoSQL database. Cassandra is built from day 1 to be clustered to tick the usual clustering boxes; no single point of failure, and capacity and throughput scales with cluster size. This guide will look at creating a three node basic cluster within a single data centre. It is assumed
Cassandra uses various ports for communication, either server to server communication or client to server communication. If you’re using Cassandra in a firewalled environment you may need to open various ports depending on your needs. All ports are TCP and can be configured in the relevant config files to use non-default ports.
The following process will install the DataStax distribution of Cassandra on any Debian based system, such as Debian or Ubuntu. We’ll use the official DataStax apt repositories to install Cassandra using apt-get. Cassandra is written in Java and the latest version (at the time of writing) of Cassandra requires Java 8. You can use either OpenJDK or
I keep finding new uses for GitHub Pages - situations where in the past I would otherwise have spun up a web site on heroku or similar. But if the site can be static, and especially if you are already hosting the git repository at GitHub, Pages are perfect.
For a long time, I've maintained the LittleArduinoProjects project index as a simple table in the README. But it wasn't particularly nice or usable, so I (more...)
I'm working on an idea where I need to measure temperatures to around 500°C - above those typically supported with semiconductor sensors or thermistors.
This project demonstrates the basic approach using an Arduino as the "temperature logger". I'm using a K Type thermocouple that's rated up to 700°C. Since thermocouples only measure a differential temperature, I'm also using an LM35 to provide the cold-junction baseline. The temperature measurement is displayed on a 5110 LCD.
One of the best finds in the racks at Tower Records Fukuoka福岡市. It's been years since I last got to browse a record store in Japan; I'm glad they still exist, with stacks of CD players queued up to sample. And a huge relief to see the indie rock scene is just as vibrant as I remember!
Solenoid engines? They definitely fall into the the category of because you can. Some people take it to a whole other level (like this V8 model).
What I have here is much more modest - a single-cylinder engine powering an impromptu-wire-art drive train. The mini-solenoid used here has a very small effective stroke - about 8mm - which necessarily constrains the gearing. I was inspired by 30GB's similar model for the layout.
A Wien bridge oscillator is essentially an RC Band Pass Filter with a high Q factor at the resonant frequency, and generates a nice sine wave. I wanted a simple audio-frequency test signal generator, and a Wien Bridge turned out to be perfect for the job.
Here's yet another way to drive a 7-segment single-digit display unit - using a CD4026.
The CD4026 is a 5-stage Johnson decade counter with decoded 7-segment display outputs and display enable. With RESET and CLOCK INHIBIT low, and DISPLAY ENABLE IN high, the 7-segment display outputs progress through the 0-9 sequence on the rising edge of the CLOCK pulse.
It's an interesting alternative to a shift register for driving a 7-segment LED (as in (more...)