S3238680 FLEX Sensor report - project 4
From Physical Programming
By Warwick Perrin S3238680
Capacitive Touch/Force Sensors
A Report on the Force Sensitive Resistor
How the device works
”The harder the force, the lower the resistance”
This sensor works by sensing the human body. When the user touches the sensor, data is transferred to an output to inform the user that the sensor is functioning. This can be relayed to the user for example as audio or visual cues.
A FSR (Force Sensitive Resistor) detects physical pressure, squeezing and weight (however they are a bad choice for detecting exact weight predictions). FSR’s are simple to use, and also low cost. It works by changing its resistive value in ohms depending on how much force is applied; meaning the resistance changes as more pressure is applied. When there is no pressure, the sensor reads like an open circuit. As pressure increases, the resistance goes down. See graph:
What is the device typically used for?
These sensors can create very interesting and an interactive work Capacitive touch sensors are normally used in simpler button/switch interfaces, which are available on most portable gadgets like a mouse, the ipod, and the On/Off switch for your LCD monitor. This method senses the change of capacitance when the user’s body (ie finger tip) comes in close contact on the switch plate surface. FSR’s can be used to create drum pads, which help to create velocity sensitive pads.
Interface with the Arduino microcontroller
Using the FSR for my final project, connection to the Arduino is easy and can be done a variety of ways. This is due to the fact that they are non-polarized. Methods of connection vary from using a terminal block, clamp style alligator clips, or by plugging them into a breadboard. I think I will choose to connect them to a breadboard using lengths of wire so that I can be free to move the sensor to a desired position.
Here is an example of how I could connect the FSR to my Arduino:
It is possible to construct a touch sensor using the Arduino and two piece of wire. I could insert the FSR sensor into a breadboard, terminal block, or alligator clips and connect it to the Arduino with an LED Light attached also. Using a desired code with the Arduino software on the computer, this is then uploaded to the Arduino hardware. Now that the program is successfully uploaded to the Arduino, I can now apply force to the sensor and then view the computer display for feedback!
One example of It’s use with the Arduino
As mentioned earlier, the FSR sensor is a great way to add velocity sensitive pads to a drum machine / sampler. But I found another example which uses a similar method. It is called the VandalSpray.
The spray can is built upon the Arduino platform and uses different sensors and electronic modules like a a super bright RGB LED, a Rotary Encoder, a Bluetooth module, and a force sensitive resistor (FSR).
VandalSpray is a digital spray can specifically designed to paint ‘digital canvases’. It implements the attributes of a real spray can or at least tries to achieve them as natural as possible. Except a rotating bottom for changing the colour, VandalSpray has no other interfacing elements than its real counterpart and therefore you don’t have to learn and explore the functionality first, because you intuitively know how to use it.
References:
http://www.openobject.org/physicalprogramming/Hardware-Sensors http://www.siongboon.com/projects/2007-11-29_touch_sensor/index.htm http://www.ladyada.net/learn/sensors/fsr.html http://www.sparkfun.com/commerce/product_info.php?products_id=9375 http://blog.formatlos.de/2008/12/01/digital-graffiti/
