Sensors

The Touch Sensor:

They work much the way you would expect, like a button that, when pushed, connects a circuit that sends a voltage to the computer. When not pushed, the button sends nothing to the computer.

The Infrared Proximity Sensor (Light Sensor): Infrared (IR)

Optical sensors take advantage of invisible light waves to sense objects in their environment. These are very effective for use in non-contact object sensing, and are also useful for navigation when high contrast lines are placed on the floor. As all surfaces reflect a certain intensity and wavelength of visible light based on their texture and color, they also reflect light in the IR range (wavelength > 750 nm) based on these same features.

The Ultrasonic Range Sensor:

Ultrasonic sensors measure object distance by calculating the time it takes for a sound wave to strike the object and return to the sensing element. The most common type of ultrasonic sensor was developed by Polaroid for use in their auto-focus cameras as a method of measuring the distance to an object on which to focus. These sensors use electrostatic material that, when excited by a voltage, vibrates to send sound pressure waves out from the sensor to a range of 10cm to 10M.

The Infrared Range Sensor:

Optical sensors are superior to ultrasonic sensors in that they do not depend on calculating time-of-flight of a wave. There are IR sensors that take advantage of triangularization to determine the distance to a target. By using an IR LED to transmit an IR beam toward an object coupled with an array of photodiodes to receive the reflected IR light, IR range sensors can calculate the distance to the object. It works like this: the IR LED emits a modulated beam of IR light that strikes objects in its environment.

The Ultraviolet Sensor:

Many ultraviolet light sensors are available one happens to be the ultraviolet band (185-260 nm) in which flames emit, and therefore this sensor proved invaluable in our flame-detection application.

The Phototransistor:

A phototransistor is a device in which current flow is directly proportional to the amount of light incident on the surface of the sensing element. The brighter the light, the higher the voltage sent to the computer. These can be used in an array to produce greyscale images, in which a more white pixel on the screen would represent a phototransistor experiencing brighter incident light.

The Strain Gauge:

Strain gauges operate on the principle that a wire's resistance changes as its diameter changes. That is, if a wire with a given current running through it is stretched or compressed, the potential measured at its ends will change. Mounting one of these strain gauges to the fixed end of a long beam serves to amplify the stretching effect through mechanical advantage. They serve an important role in measuring stresses in materials and also reliably measure forces on objects.

The Accelerometer:

Accelerometers measure the acceleration along a given axis. Most examples are fairly straight-forward in their operation and interpretation. Early models used a strain gauge-like setup with a known weight on the end of a beam fitted with a strain gauge. This method, in conjunction with a timer, could measure the direction and speed of deflection, thus determining its acceleration. The latest accelerometers use a known resistor in series with a capacitive beam that deforms under its own weight.

The Encoder (Angle Sensor):

They are based on the same principle as many other sensors, using an LED and a phototransistor coupled with a special disk. This disk has many holes drilled at even spacing along its perimeter, and when the phototransistor sees the LED through one of these holes, it registers a high value. When the LED is blocked by the space between the holes, the phototransistor registers a low value. By counting these highs and lows, you can determine the number of rotations the motor has gone through, or, for instance, the distance a wheel has traveled.

© LEV