The PIR is a motion-activated switch, normally open.
This article describes the steps involved in conceiving and realizing the interactive art installation "Rain", also known as "Umbrellas". It consisted of five umbrellas hung from the ceiling, in a space about 12ft x 12ft. When installation visitors stepped under the umbrellas, sounds of rain were played back, with increasing intensity when more people participated.
This article is intended for anyone who wants insight in the parts that make up an interactive installation. The members of the team were Per Nilsson (article author), Robert Innes and Deniz Olcay.
Play to hear a rain recording used in the installation
The space for the installation was a corner with large windows at the SFU School of Interactive Art and Technology campus, in Surrey BC. There were five umbrellas of different types hanging from a framework of pipes in the ceiling. Cables were out in the open but wrapped around the mounting pipes to conceal them. The computer used to play rain sounds was placed behind a pillar in the middle of the space. Speakers were placed on the four corners of the space.
The installation was shown a total of two days, with a week in between to iron out initial problems. It was received with comments like: "Its like I'm in the forest!", "It makes me want to play", "I'm afraid of getting rained on"; and "Nice addition to the space".
The installation started as a vision: "What a poetic/magical/eerie/weird/awesome feeling it would be to unfold an umbrella indoors, and hear the drumming of rain on it! You could bring that cozy, protected-personal-sphere feeling with you anywhere. It would also mess with your mind to think that you were outdoors, when you were indoors"
During the course of realizing the project, the idea changed from a portable rain-umbrella to an installation that let many people simultaneously experience the sounds and ambience of rain on umbrellas.
The PIR is a motion-activated switch, normally open.
An infrared motion sensor is standard equipment in any home alarm system. We used a small, bare-bones version of the wall-mounted sensor, a PIR.
The PIR sensor uses infrared light to detect motion. On the inside, there is some circuitry to trigger a switch when movement is detected, but this complexity is hidden. All you need to know is that it works just like a switch, which closes when something moves in front of it.
The switch stays closed as long as the sensor detects motion. When the motion stops, or moves outside of the sensor's field of view, there is a delay of a few seconds before the switch opens again.
The signal from the sensors were routed to an Arduino microcontroller board. Arduino is a cheap, open-source, prototyping hardware and software system.
Prototype materials: PIR sensor, Arduino, breadboard, 10kΩ pull-down resistor. We chopped up an Ethernet (regular network) cable to connect the sensor to the Arduino Board. This is a cheap (often free) way to get long cables for installations.
Close-up view of first prototype. It soon became clear that the sensor was triggering before we stepped under the umbrella, which led to the second iteration.
Prototype, second iteration. Note the paper cone around the infrared motion sensor, limiting its effective field-of-view to the circle immediately underneath the umbrella.
Prototype = Early Form. Depending on the complexity of the project, you need to make one or more prototypes. Ideally, you have enough time to iterate through several prototypes, improving your idea every time. At the very least, you will use your prototype as a sort of real-world sketching board, to test out new ideas as they come to you. At this time, you are not concered with beautiful form, but with function. As your prototype improves, you will be increasingly concerned with quality of interaction (percieved response to stimulus and performance). Form, or making it beautiful, will have to wait.
Everyone does prototyping in different ways, and every project has different possibilities for prototyping techniques. Some prototypes model an experience, and imagination provides the functionality. Other prototypes have more of the intended function, and will slowly metamorphosize into the final form.
A design firm that takes prototyping seriously, and uses rapid prototyping techniques for communicating proof-of concepts internally and to clients, is IDEO.
The hardest part of the project was to create a seamless experience for installation visitors. The motion sensor switches only stayed closed as long as something was moving, and when people stood still under the umbrellas, the sound stopped. We solved that problem by imposing a delay before the sounds stopped, even if the program received a "stop" signal from the sensor. We also made the sounds fade in and out rather than being turned on and off abruptly.
Another problem we had was that some sensors were tripped by the umbrellas dangling (they detected the relative motion of the floor). For the second iteration, we made this better by hanging each umbrella from two lines, thus stabilizing them.
Diagram showing all parts of the Rain project and how they connect - umbrellas with motion sensors, Arduino board, laptop with Max/MSP, and speakers.
Circuit diagram showing 5 PIR sensors connected as normally-low digital switches to an Arduino board, sharing a 10kΩ pull-down resistor
Circuit diagram showing a PIR sensor connected as a normally-low digital switch to an Arduino board, with a 10kΩ pull-down resistor
Download the Rain MAX-patch, the Rain MAX-patch with sound files, or to make your own Arduino-Max project, download Arduino2Max. Max/MSP is an expensive program, but there is a free software called Pure Data that does almost everything MAX does. Here's a link to the Arduino-PD interfacing page with patches like Arduino2PD.
You can download the programming environment for Ardiuno from arduino.cc.