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= Resistors = | == Resistors as parts == | ||
German: Widerstand, Widerstände | German: Widerstand, Widerstände | ||
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2.2 MΩ is written 2M2 | 2.2 MΩ is written 2M2 | ||
== Common Appliances == | |||
* Pull up / Pull down for digital IO | |||
* current limiting (LED, Transistor, directly dimming lamps and small motors) | |||
* Voltage dividers for reference voltages | |||
* Sensors made of changing parts changing their resistance. | |||
== Resistive Sensors == | |||
Resistive sensors with large resistance changes (doubling the resistance during use or more) are easy to connect to an an analog input. A simple voltage divider is sufficient to read the resistance value in this case. | |||
Resistors with small changes of resistance need additional circuits to amplify the small changes measured on the voltage divider. This can be achieved with an operational amplifier and a bunch of resistors and potentiometers for calibration. | |||
=== Potentiometers === | |||
Standard Linear and Rotary Potentiometers | |||
Magnetopot | |||
=== Touch === | |||
Rotary and linear touch sensors. Similar to connect like Potentiometers: When touched they react like a potentiometer, when not touched the "middle pin" of the potentiometer doesn't touch the resistive layer at all. Single and dual touch is detectable. Single touch is like measuring potentiometers, dual touch needs 2 ADC-Channels and some calculations for the resistances in series. | |||
=== Temperature === | |||
PT100 and PT1000: Made of thin platinum wire. Low resolution compared to other sensors when directly hooked up to an analog input since change of resistance is small. Can be used to make measurements very precise when pre-amplification is used. Industry standard - simple to replace when broken, pricey. | |||
NTC and PTC Thermistors: NTC Lowers Resistance when heated, PTC increases resistance when heated. Simple to use, cheap, not very accurate (5%), nonlinear, but can be linearized, usable for many appliances where high accuracy isn't important. | |||
http://reprap.org/wiki/Thermistor | |||
=== Light === | |||
LDR (Light Dependent Resistor) | |||
Available in different dark/bright resistance values. Bright resistance: The resistance of the sensor when lit with a defined amount of light (Usually 25 Lux are used as "bright"). Varies from 1k to several 100k for 25 Lx. | |||
=== Pressure / Force === | |||
DIY Sensors from resistive Materials: | |||
http://www.kobakant.at/DIY/?tag=velostat | |||
Conductive Foam | |||
Velostat | |||
Cunductive yarn | |||
Conductive(!) video Tape - beware: most tapes aren't conductive. | |||
=== Elongation / Strain === | |||
Strain gauges: Made of thin resistive wires, resistance increases when enlongated. Very small change of resistance - needs to be amplified for mikrocontroller's ADC. Used in personal scales to measure weight, also usable as bend sensor when glued on solid surfaces. | |||
=== Bend Sensors === | |||
change of resistance when bent, destroyed when fold. Small hysteresis, appearing when unbent. | |||
Power Glove: contains 5 of those sensors - one for each finger, can by bought in different lenghths. | |||
DIY: Velostat and shrink tube - less accurate, some hysteresis. | |||
== Resistor Color Codes == | == Resistor Color Codes == | ||