Input Sensors: What to use and why

• Accelerometer

          - MEMS (MicroElectroMechanical System)

          - Usually 3 Degrees of Freedom (3DOF)

          - Measures acceleration, usually in ”g”

                   + 1g = 1 standard, sea-level gravitational pull towards earth.

                   + Weight = Mass X Acceleration (from gravity) (w=ma) (you have the same mass on earth and the

                      moon but weight more on earth) Gravity is ~ 9.8m/s2

• Gyroscope

          - MEMS (MicroElectroMechanical System)

          - Usually on the same chip as the accelerometer! (6DOF)

          - Degrees per second rotation (non-persistent)

                   + 6 degrees per second = 1RPM

                   + 360 degrees per second = 60 RPM

• Ultrasonic

          - Cheap $3.50ish

          - Reasonably accurate (3mm)

          - Good range (5m)

          - May suffer from noise issues

                   + Especially when using multiple

          - Work as fast as trigger to receive time

                   + Distance = travel time / 2 * Speed of Sound (343m/s)

 

• Colour sensing

          - Subject to ambient light issues

          - Cheap units have low “resolution” of colour spectrum.

          - Good single sensor choice for multiple object detection in controlled environment.

 

• Infrared beam break

          - Fast

          - Variable range / function

                   + Beam break

                   + Distance

          - May be Subject to interference 

                   + External sources 

                   + Other devices

                   + Ambient conditions

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• Reflectance: sensing distance

          - Light or Infra Red

          - Can be used to sense distance

          -  Subject to interference

          - Can be very accurate

          -  Lasers can be used

                   +  Time of flight measurements

                   + LIDAR

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• Force Sensitive Resistors (FSR’s) & Membrane Potentiometers

          - Expensive! $$$

          - Fairly accurate

          -  100g to 10kg

          - Too much force will destroy it

          - Readily available

          - Resistor divider configuration

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• Velostats and stretchy things

          - Velostats are conductive materials made of polymeric foil and carbon black.

          - Originally used as anti-static packaging

          -  Great for prototyping:

                   + Cheap

                   + Workable (cut to size)

                   + Easy to read (use in a resistor bridge)

                   + Great for clothing and flexibility

                   + Surprisingly strong

          -  Check Adafruit, core-electronics, etc.

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• Sliders (faders), Potentiometers & Encoders

          - Sliders and potentiometers:

                   + Cheap

                   + Reliable (in the right conditions)

                   + Available in a huge range of shapes and sizes.

                   + Electro-mechanical

                   + Require little code

                   + Fairly high resolution (1024 steps for 300°)

          -  Encoders:

                   + Can range dramatically in price

                   + High resolution

                   + Opto-mechanical

                   + Require lots more code

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• Barometric pressure

          - Range from cheap and inaccurate to expensive and very accurate.

          - Used in devices from fighter jets to washing machines.

          -  Good for detecting change in environment:

                   + Burglar alarms

                   + Weather

                   + Impact pressure in punch bag?

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• Biometrics – pulse / heart rate

          - Cheap < $15

          - Use reflectance!

          -  Some can do blood oxygen concentrations

          - Track changes in heath over periods

          -  Established, understood technology

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