Infrared Illuminator

Infrared (IR) illuminators are
widely used to improve the imagecapturing
quality of security cameras
fitted in dark zones. Just like our
eyes, cameras also can’t record movements
movements
in dark.
However, unlike
our eyes,
most of the latest
cameras can
capture infrared
light.
I n a n I R
I l l u m i n a t o r ,
many infrared
IR LEDs are grouped together to throw
good amount of IR light. Typically,
LEDs output at 470 nm (blue region),
525 nm (green region) and 625 nm
(red region). IR LEDs produce longer
wavelengths, 880 nm and 940 nm being
the common ones. Most CCD cameras
are a little more sensitive to 880 nm,
although when these LEDs are used
for security applications, some individuals
can detect a very dim red glow
from them. The 940nm LED radiations
are completely invisible to the eye.
Some of these LEDs are clear, while
others are tinted with pale shades of
dark gray, blue or even black. They
come in various configurations and
radiation patterns, but 5mm types with
15- to 40-degree patterns are the most
popular.
Typically, IR LEDs run at around
1.3 to 1.7 volts, depending on the
LED current (typically 10 to 30 mA).
However, this may vary with the type
and manufacturer. Practically, IR illuminators
may have 6 or 60 to 100 or
more LEDs, depending on the output
needed.
The circuit (refer Fig. 1) can be
divided into three parts: ambient light
sensor, relay driver and IR LEDs. The
ambient light sensor is built around
multiturn linear potmeter VR1 and
light-dependent resistor LDR1. The
relay driver section is built around
transistors T1 through T3. The IR LEDs
section is built around LED1 through
LED40.
The light sensor circuit is a simple
transistor switch with the base of the
Darlington pair (formed by T1 and
T2) connected to a voltage divider.
Variable resistor VR1 and the 10mm
encapsulated LDR are used to sense
the ambient light. As light falls on the
surface of LDR1, its resistance changes.
The amount of minimum light needed
to actuate the relay through driver
transistor T3 can be varied by adjusting
VR1. Diode 1N4001 eliminates
any back voltage when the relay
de-energises. Switch S1 is the mains
power on/off switch and switch S2 is
added to bypass the ambient light detection
function.
Relay RL1 energises only when
the ambient light level falls below a
threshold value set by VR1, i.e., when
it’s dark. Normally-opened (N/O) contacts
of the relay ground path to the IR
LEDs (LED1 through LED40) to make
them glow. The blue LED (LED41) indicates
the circuit activity. When there
is ambient light and you want to use the
illuminator, switch S2 ‘on.’ All the LEDs
(LED1 through LED40) glow to fulfil
your requirement.
Assemble the circuit on a generalpurpose
PCB and enclose in a suitable
cabinet. The IR LEDs assembly is very
important. A set of 40 (5×8) 5mm infrared
LEDs (IR LED1 through IR LED40)
with independent current-limiting
resistors (R3 through R10) per string
is used. This section is powered by
the input DC supply through the relay
contacts.
Mount IR LEDs on the general-purpose
PCB board such that these make
three circles. After soldering, carefully
cut the outside of the circuit board in
a round shape and fit it in a suitable
metal/plastic cabinet. If available, adda suitable reflector sheet for the IR
LED bank. Finally, fit the LDR bank
on top of the enclosure with switches,
indicator-sensitivity-control pot and
power input socket. Fig. 2 shows the
infrared illuminator unit.To make the circuit actuate the relay
when the intensity of ambient light
is less than the preset light level, throw
light on LDR1 and then slowly adjust
the potentiometer until LED1 lights up
and the relay energises.

Computer Engineers Develop Clothes that Sense and Interpret Movements

April 1, 2006 — New "electronic textiles" could help monitor the activities of patients with chronic illnesses. Computer engineers have developed pants with sensors embedded in the fabric that measure speed, rotation and flexing, and send wireless signals to a computer. Researchers plan to integrate computers into shirts, hats and gloves


BLACKSBURG, Va.--You get a cell phone call and your sleeve answers it. You want to know how far you jogged and your pants tell you. Smart clothes are the latest trend to come down the runway.

Can't decide what to wear? Wish your clothes were smart enough to decide for you? Now, electronics and computer science technology may help your clothing think.

Mark Jones, a computer scientist at Virginia Polytechnic Institute and State University in Blacksburg, says, "We view electronic textiles as, sort of, where computing meets the fabric."

This high-tech marriage is breeding the latest in wearable computers, like pants that detect movement and let a computer know your every move.

A loom helps sew the wires and fabric together. Then sensors embedded in the fabric measure the speed, rotation and flexibility of the pants with every movement. Wireless signals are sent from the pants to a computer to display the activity.

Tom Martin, also a computer engineer at Virginia Polytechnic Institute and State University, says, "E-textiles are a way for us to build wearable computers that look like normal clothing to build pervasive computing devices that fit in seamlessly with the environment."

Researchers also hope wearable computers will help save lives. "We can tell what activity that person is doing. That sort of information is extremely valuable when we're trying to monitor someone with a chronic illness such a heart condition," Jones says. And monitoring your every step is something clever clothing can watch a little easier.

Researchers plan on developing more smart clothes to integrate computers into shirts, hats and gloves.

BACKGROUND: Scientists at Virginia Tech's E-textiles Laboratory are developing clothes that appear and feel normal, but provide sensing and computing capabilities. Wires and sensors are woven into the fabric, which can then be used to make shirts, pants, hats, gloves or other clothing items. It turns clothing into "wearable computers," capable of monitoring things like how fast and how far a jogger runs, or the blood pressure and heart rate of a cardiac patient.

ADVANTAGES: Smart clothing/wearable computers are already on the market, but the current e-textiles in use have problems. Some sensors only work well if they are placed a certain distance apart on a garment. If the user rolls up the shirt sleeves or pants legs, or other changes occur while the e-textile garment is being worn, the network of sensors needs to be able to "sense" the reconfiguration and adjust accordingly in order to perform effectively. The e-textiles being developed at Virginia Tech will be able to sense their own shapes, the wearer's motions, and the positions of the sensing elements.

WHAT'S NEXT: The Virginia Tech researchers are working with a major textile manufacturer in Virginia, Dan River, Inc., to determine whether e-textiles can be made using traditional manufacturing techniques. To that end, they will test a prototype e-textile fabric on Dan River's existing looms. If this works, wiring will be woven into the fabric using the looms, and the sensors will be attached after the garments are completed.

HOW SENSORS WORK: Sensors are tiny electronic devices that can both detect and generate electrical signals from the movement and position of any given object, including the motion of the human body. These signals are then transmitted wirelessly to a microcontroller and analyzed using specially designed algorithms.

Journal of Electronic Materials

The Journal of Electronic Materials (JEM) is a monthly archival publication that reports on the science and technology of electronic materials, while examining new applications for semiconductors, magnetic alloys, insulators, and optical and display materials. The editor in chief is Suzanne Mohney

Published by the Electronic, Magnetics & Photonic Materials Division of The Minerals, Metals & Materials Society (TMS) and the Institute of Electrical and Electronics Engineers (IEEE), the journal contains peer-reviewed technical papers detailing critical new developments in the electronics field, as well as invited and contributed review papers on topics of current interest, designed to enable those in the field of electronics to keep abreast of activities in areas vital to their own technical interests.

Articles that appear in JEM are reviewed, selected, and edited by peers in the field who serve as voluntary members of the editorial board or the board of associate editors or as section editors. Generally, they are members of the Electronic Materials Committee of TMS or are members of IEEE.

CURRENT TRENDS IN INTEGRATED OPTOELECTRONICS

This compilation of review articles by leading experts presents clearly the trend in future optoelectronic devices. It is clear that optoelectronic and photonic integration help to further improve high-speed system capabilities and increase the total systems and network capacities with WDM technology. The foundation of the integration technology is based on quantum well materials, and advanced epitaxial growth and device processing techniques. The integrated laser/ modulators, multi-wavelength laser arrays, and OEIC receivers have demonstrated the feasibility of this technology, but much work remains to be done to put such technology to practice.

Contents:

* High Speed Semiconductor Lasers (R Nagarajan et al.)
* The Progress and Performance of Long Wavelength OEIC Photoreceivers Incorporating Heterojunction Bipolar Transistors (S Chandrasekhar)
* Multiwavelength Light Source with Integrated DFB Laser Array and Star Coupler for WDM Lightwave Communications (C E Zah et al.)
* Monolithic Integration of DFB Lasers and Electroabsorption Modulators Using In-Plane Quantum Energy Control of MQW Structures (M Aoki et al.)
* Monolithic InP Reflection-Grating Multiplexer/Demultiplexers for WDM Components Operating in the Long Wavelength Fiber Band (J B D Soole et al.)

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