Friday, October 22, 2010

Sensors Part 1 - Interaction with the Physical World

We use sensors everyday and they are so common that we sometimes forgot about them or didn't even know they existing until the sensors stop working... here are some sensors that we encounter in our everyday life... let start with the most popular ones.

Button sensors

You might think this is not a sensor but just a button but it is the most important sensors to the computer. We input our characters via a keyboard, a collection of buttons! A few tricks can be performed by the button sensor to have different behaviors.

Big button sensors, push button and numeric pad

  • pushing a button to turn a LED on or off ( AKA on/off pushbutton switch )
  • holding a button will turn on the LED, releasing the button will turn off the LED
  • holding a button to adjust the brightness of the LED or two button volume control on laptops
  • double click the button to select a menu or just to the next sound track, this is commonly found on the mouse buttons or mp3 players to skip a track a song.
  • triple click on the button, this can be found on Apple iPhone headset/mic to play the previous sound track.
  • buttons arranged in four directions to navigate up/down/left/right
This will give you some idea on how you can program the behavior of just a simple button sensor. You can buy Arduino button sensors, a big yellow button for educational purpose. What you use it for is up to your creativity.

Rotary Sensors

This is probably the second most common sensors that are found anywhere from volume controls to old generation of iPad. Apple designers found out that it is much easier (and faster) to select songs using a rotary sensors that an bunch of arrow keys. All our mouse have a wheel in the middle made for scrolling functions. An earlier version of rotary sensors was found in the side of older Sony products called the jogdial, a single hand operation to combine the push button with a rotary sensors.

Rotary sensors

The above is the rotary sensors for Arduino to be used as input interface for your projects.

Touch Sensors
These sensors are found in all touch screen phones and touchpad below the laptop keyboard. The last few generation of iPod uses touch sensors as a replacement for rotary sensors.

The latest generation of touchscreen smartphones uses a capacitive touch screen while older touch screen phones uses a resistive touch screen that depends on the pressure of the stylus/pen. 

Range Sensors

Sharp IR range sensor

This sensors are activated when we shift to the reverse gear, they are called reverse sensors or parking sensors. Similar sensors are used in art gallery to detect when a person is near the art work or within the predefined range. For robotic, these sensors can be used to detect the distance of an object in front of the sensors.

Range sensors works by sending a source of light or wave and measuring the signal that was reflected back and comparing it with the energy that went out. The common ones are like Sharp GP2D12 (10 to 80cm) and other depending on the IR range.

Motion Detectors (PIR)
PIR sensor

These sensors are commonly used in burglar alarms, automatic lightning and those annoying sensors in 7/11 that plays a tune when someone walks into the store. They are use to detect presence of a person within a range. They are called Passive IR or just IR motion sensors. The white dome is a lenses that focus the energy to a pyroelectric sensors that detect changes in IR radiation. have a detail article about the PIR motion sensors.

Photoelectric Switches

Photoelectic switches
These sensors are most commonly found on newer elevators that will stop the elevator door from closing when the beam is cut.

Laser and light dependent resistors (LDR)

A cheap and easy way to make one of these sensor is using a laser pointer and a light dependent resistors or photocell. Once the laser is cut, the photocell will detect the change in light and trigger an alarm. This is both fun and easy to make.


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