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    Content by Mika Satomi and Hannah Perner-Wilson
    The following institutions have funded our research and supported our work:

    From 2013-2015 Mika is a guest professor at the eLab at Kunsthochschule Berlin-Weissensee

    From July - December 2013 Hannah was a researcher at the UdK's Design Research Lab

    From 2010-2012 Mika was a guest researcher in the Smart Textiles Design Lab at The Swedish School of Textiles

    From 2009 - 2011 Hannah was a graduate student in the MIT Media Lab's High-Low Tech research group led by Leah Buechley


    In 2009 Hannah and Mika were both research fellows at the Distance Lab


    Between 2003 - 2009 Hannah and Mika were both students at Interface Cultures
    We support the Open Source Hardware movement. All our own designs published on this website are released under the Free Cultural Works definition
    Circuits and Code

    Pull-up Resistors

    Voltage divider, variable resistor, pull-up, pull-down….???


    External pull-up resistors

    There are various ways to wire or sew external pull-up resistors:



    Diagram of a Pull-Down resister for a switch

    You need a pull-up or pull-down resister when you want to read a contact switch or button (i.e. push button). If you have pull-up resister, you will see 0V(LOW) when you push the button. If you have pull-down resister, you will see 5V(HIGH) when you push the button on your digital pin reading. Here is a diagram showing why you need a pull-down resister.


    Internal Pull-Up Resistors

    For the longest time I had no idea that I could simply set internal pull-up resistors using a single line of code! But the Atmel chips that arduino uses have internal resistors that can be toggled on or off for every digital and analog input pin (except A6 and A7 on some boards).

    Digital
    For setting the internal pull-up resistors for digital input pins, the code will look like the following:
    pinMode(2, INPUT);
    digitalWrite(2, HIGH); // turn on internal pullup resistor for digital pin 2

    *NEW*: pinMode(2, INPUT_PULLUP);

    Analog
    For most of our fabric sensors using velostat the internal 20 K Ohm pull-up resistors of the Arduino are just fine. To set these you’ll need to include the following lines of code in the setup function of your Arduino sketch. The analog inputs 0-5 can be addressed as digital outputs using the numbers 14-19:
    pinMode(A0, INPUT);
    digitalWrite(14, HIGH); // set internal pullup resistor for analog pin 0

    *NEW*: pinMode(A0, INPUT_PULLUP);

    Understanding Voltage Measurement

    Ohm’s Law: V = I x R

    Voltage divider:

    Diagrams explaining voltage divider and pull-up resistor:


    Links

    >> http://arduino.cc/en/Tutorial/AnalogInputPins
    >> http://arduino.cc/en/Tutorial/DigitalPins
    The following CNMAT and Wikipedia entries cover all the important explanations of why you need and how to place pull-up or pull-down resistors.
    >> http://cnmat.berkeley.edu/recipe/how_and_why_add_pull_and_pull_down_resistors_microcontroller_i_o_
    >> http://en.wikipedia.org/wiki/Pull-up_resistor

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