openobject.org

S3149209 Sensor report - PROJECT 4

From Physical Programming

LDR - Light Dependent Resistor

An LDR is a Light Dependent Resistor that electronically detects changes in light. It is a cheap light sensor which varies its resistance depending on the amount of light falling on it. As light increases the resistance of the LDR decreases. This feature makes LDRs suitable for use where an automatic light changing function is needed. An LDR can output information on distance, shape, speed, dimensions but are more commonly used to monitor variances in light. LDRs are made up of semiconductors of light-sensitive materials, put together on an isolating base. Commonly used semiconductors are cadmium sulphide and lead sulphide.

The simplest form of circuitry for an LDR would be a circuit with an LED connected in series to the LDR. If when the amount of light increased the resistance of the LDR decreased this would be known as a negative co-efficient. This change in resistance completes the circuit, lets current flow through the LDR and would light up the bulb. In this case the LDR acts as a switch that is turned on with light and off with dark, so having the LED on in the light would be pointless. For this reason there are LDRs that work in the opposite way, their resistance increases with light and are so called positive co-efficients.

LDRs are commonly used in light activated switch circuits such as outdoor lighting, street lamps, smoke detection devices, burglar alarm systems and some kids toys.

However LDR can also be used in packaging lines to count the number of products made. It can be set up to detect markings on products so each time the target passes the LDR it registers and counts it as one. Because of its high speed and precise sense of light LDRs are the simpler, cheaper and more efficient alternative to having a human worker.

On a higher level LDRs are even used in space exploration as they can make topographical maps of planetary surfaces and measure the quality of light coming from given stars, planets, and comets.

Some other applications:

  • Analog Applications
    • Camera Exposure Control
    • Auto Slide Focus - dual cell
    • Photocopy Machines - density of toner
    • Colorimetric Test Equipment
    • Densitometer
    • Electronic Scales - dual cell
    • Automated Rear View Mirror
  • Digital Applications
    • Automatic Headlight Dimmer
    • Night Light Control
    • Oil Burner Flame Out
    • Position Sensor


Using an Arduino the LDR can be used to turn on and off a circuit in the presence and absence of light. It can also be coded to uses its different levels of resistance to vary the output similar to a high/low slider in 'pd'. The Arduino takes output information from the LDR and depending on the reading it then sends a corresponding message through the curcuit to tell the objects what to do.

Using my third YouTube video link as an example the Arduino is connected by two wires to a "bread board" which is being used as a connection base for any electronics in the circuit - in this case its the LDR. There is also an LED plugged directly into the output jack of the Arduino. After running the programming the Arduino will be constantly taking in readings from the resistance output of the LDR and relaying it through the LED in a visual response. Depending on the resistance (high to low) the message sent out will be different whether its to make the LED flash faster or slower.


This video demonstrates the use of an Arduino board with a negative co-efficient LDR. Also connected in the curcuit is an LCD display which shows/highlights the different levels of output from the LDR.

http://www.youtube.com/watch?v=Re3XzxIorqk

This video demonstrates the use of an Arduino board with a positive co-efficient LDR similar to what i would like to achieve with me curcuit.

http://www.youtube.com/watch?v=CP6NtvfEylM

This video demonstrates the use of an Arduino board with an LDR and an LED. In this case it’s used to sense the distance of an object and relate that back to the user through the LED. The closer the object the faster the bulb flashes.

http://www.youtube.com/watch?v=wLAjnOWO8mU

IMAGES:

WEB:

TEXT:

  • MDPI. SENSORS; Derci Felix da Silva and Daniel Acosta-Avalos, France, 2006; pp. 1-2.
Retrieved from "http://www.openobject.org/physicalprogramming/S3149209_Sensor_report_-_PROJECT_4"