Project Research-Sensors

First I need to decide what kind of sensors will be idle for my project

 

When the spectators get close enough to the painting, the animation start. Consequently we need something, which can found out where the spectator is in relation to the screen. This interaction will give the computer the ability to sense the position of the spectator in space.

 

Detecting Presence

 

Web cam

 

My first thought was to use a web cam to detect motion, unfortunately the information would not be accurate enough, and I am not sure how the camera will handle more than one visitor at the time. This will create more problems, especially regarding the environment. If I choose to use a web cam with some software such as Isadora, Eyesweb or even Quartz Composer I would need to constrain the space to make the most effective use of it. Only one person at the time would be allowed, which will take away the surprised effect, the unexpected will be in a way expected.

 

Foot Switch

This  device is very straightforward, and will trigger any action within a small area. One of the most common type is made of long stripes of metal separated by foam tape. When someone step s on these sensors, the foam tapes is compressed and the metal strips are touching each other’s.

This seems a cool website to get that kind of switch, but to be honest I do not dare asking for the price

http://www.tapeswitch.co.uk/Ribbon_Switch/Ribbon_Switches.htm

The mat switch would be idle underneath a carpet, but I believe my budget would not allow it.

 

Determining Position

 

Infrared (IR)

IR sensors are very good for short distance sensors. These kind of sensors send out an infrared beam and read the reflection of the beam off a target, in our case the spectators.  Sharp IR sensors have been recommended in some books such as “Physical Computing” By Dan O’Sullivan and Tom Igoe.

http://www.acroname.com/robotics/info/articles/sharp/sharp.html#e14 

Some ranging formula comes from an excellent article on Acroname’s site.

http://www.tigoe.net/pcomp/code/archives/arduino/000714.shtml

 

Unfortunately the range cover by this kinds of sensor is too small up to 1.4m.  As I need to sense presence about 2 to 3 meter. Consequently the only alternative is the Ultrasonic sensor.

 

What I will need, I believe is a Range Sensor

 

Most of those sensors send out some form of energy, to be able to read the distance from a target. This could be light, magnetism or even sound. Those sensors will convert the distance into an electrical voltage or digital signal, which can be read by a microcontroller.

Similar principal of a airplane radar. This system operates by sending out a radio signal and measure the time it takes to bounce back from a target.

 

Radar

Short for “Radio Detection and Ranging: Radar, like sonar, uses a pulse of radio energy to map distance based on the length of time it takes the pulse to return from the source. Radar is based on the principle of sending very long wavelength radiation (called microwaves) from an antenna, and then detecting that energy after it bounces off a remote target. The wavelength of the microwave, its strength can be measured when it returns.

 

The radar will allow me to calculate the exact positions of visitors, and consequently will trigger the animation at the right time.

http://www.ieee-virtual-museum.org/collection/tech.php?id=2345896&lid=1

 

How much and where could I found it?

I have been told that will cost me about £200 to £300, well as much as I like the module, the student Loan would not pay for that.

 

Will it work with Arduino or the Phiget interface?

I could not found much information, but the price put me off quite a bit.

 

Ultrasound

 

They work like sonar device, sending out a ping of ultra sound, and then time how long it takes to bounce back. This kind of little device can read from 6 inch to 6 feet. . They use an initiation pin and echo pin. In the code we will have to set the initiation pin high, then use a rctime command on the echo pin to measure how long it takes to return the ultrasound.

The Daventech SRF family seems to be very popular in the robotic world (amateur’s one of course). One of the cheapest one is the SRF04.  We will need to set the init pin high, and then wait for the ping to come back. Now to determine the distance we will need to divide the time taken by the speed of sound in the microcontroller’s software.

This sensor going to be perfect, I believe, if I decide to use the Arduino microcontroller. This little tool will provide very accurate ranging information.

 

http://www.acroname.com/robotics/parts/R93-SRF04.html#bpg

 

I found a very good guide in the “physical Computing” by Dan O’Sullivan and Tom Igoe book, which might help us if we decide to use this kind of sensors.

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