Absolut Choir

Today was the first day of the RAG-TAG* workshop. I didn’t have time to see all the speakers but luckily I made it in time for Bengt Sjölén from Teenage Engineering. Here is a brief report from his talk:

Using Absolut Choir** as an example Bengt started of by talking about the importance of building scalable systems and the advantages of being able to remotely control, update and monitor installations. He then went on to highlight the benefits of using embedded Linux devices (such as the NSLU2 and the ASUS WL-HDD) instead of or together with micro controllers and PCs.

Embedded Linux devices do unlike micro controllers often have USB and networking capabilities and since they run Linux you can write full fledged applications for them in your language of choice. They usually lack the inputs and outputs that are necessary to communicate with sensors and actuators, but on the other hand they can communicate with micro controllers such as Arduinos over USB. Their advantage to PCs are their physical dimensions and their prices, which now are getting close to Arduinos.

After having having talked about embedded Linux devices Bengt finished of by discussing the possibilities of building new platforms for creative engineering around chipset such as the Sunplus SPHE 82xx which normally are found in cheap DVD players. The SPHE 82xx chipset are capable of outputting video and 6.1 audio as well as controlling servos and motors. Their limitations lie in their undocumented and closed firmware but there are now Yahoo groups dedicated to understanding and analyzing that.

An Arduino-like platform with video and audio outputs that is capable of running applications written in Processing or openFrameworks doesn’t seem that far from becoming a reality. All that is needed is a community to organize itself around some of the inexpensive embedded Linux devices and multimedia chipset that already exist on the market…

*The parents of RAG-TAG VIDEO AND MOVIE SITES are the project Grig and Performing Pictures of The Interactive Institute with support by The Culture 2000 framework of the European Commission.

**Absolut Choir is an architectural installation consisting of a robotic choir which people can conduct over the Internet. The installation and website are both impressively well built. It is currently up and running at the PUB department store in Stockholm. A lot of information about the design and technology behind the installation is available on the website.

The Parallax RFID reader is inexpensive and easy to hook up to an Arduino or Wiring board. It has four connectors which can be plugged right into a bread board and there is code for it available at the Arduino Playground. One thing that I really like about the reader is its small footprint. It is about the size of a playing card and just 2-7mm thick. The reading distance is dependent on the tags that are used, I got maximum distance of about six centimeters on the axis that is orthogonal to the reader and 2-3 cm on the parallel axis. A short reading distance can be a good or a bad thing depending on the application. If you like me want to identify a shoe with an embedded RFID tag when the wearer enters an area, then it’s a not so good thing. If you know of another inexpensive and easy to interface reader that has a greater reading distance I’d be very interested in hearing about it…

Update: I have posted some Arduino code that improves stability and fixes a couple of errors in the Arduino Playground code for the Parallax RFID reader.

Mechanical rotary shaft encoders such as the one pictured to the left are probably the cheapest way to measure rotation. This particular encoder, which costs about 2 euro, has 24 steps per revolution. The resolution is a bit of the low side for many applications but it can be increased with gears or wheels. Shaft encoders only measure relative rotation. In other words you can’t know at which position the sensor is when you first read it, but you can keep track of how much and in which direction it has turned since you started to read it.

Rotary encoders are not only cheap, they are also simple to hook up to Arduino or Wiring boards. To put it short you monitor a pin on the encoder and when it changes state you check the state of another pin to determine in which direction the encoder was turned. Paul Badger has posted some nice Arduino code for rotary encoders on the Arduino playground.

Alternatives to mechanical encoders are optical rotary encoders and 360 degree potentiometers. These encoders often have significantly higher resolution than the mechanical ones and some (such as potentiometers) can be used to measure absolute rotation. The downside is that they are more expensive (usually around 50 euro or more). A budget alternative is to go trash hunting for an old printer with a motor that has an optical encoder that you can reuse (check out this Make video). Not all printers have these motors though, I’ve trashed three so far without any luck…