Browse Prior Art Database

Active Infrared Presence Sensor

IP.com Disclosure Number: IPCOM000117090D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 89K

Publishing Venue

IBM

Related People

Levine, JL: AUTHOR [+2]

Abstract

A low-cost active infrared presence sensor with a fully automated range calibration is described. It is suitable for on/off power control of computer displays and similar equipment, especially in congested areas where its precise detection properties minimize false triggering from nearby people. In addition to saving power and extending display life, the device can be used, in conjunction with a password, to prevent unauthorized use of an unattended computer.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Active Infrared Presence Sensor

      A low-cost active infrared presence sensor with a fully
automated range calibration is described.  It is suitable for on/off
power control of computer displays and similar equipment, especially
in congested areas where its precise detection properties minimize
false triggering from nearby people.  In addition to saving power and
extending display life, the device can be used, in conjunction with a
password, to prevent unauthorized use of an unattended computer.

      A block diagram of the sensor is shown in Fig. 1.  The main
elements are single chip microprocessor 1, infrared Light Emitting
Diode (LED) 2, display operator 3, and infrared receiving module
4.  Module 4 is a commercial device intended for remote control
applications.  It emits a logic level signal when exposed to infrared
light modulated at a predetermined frequency Fe, and of sufficient
intensity to exceed an internal threshold.

      The program running in the processor drives the LED 2 via
transistor 5 with groups of pulses at the frequency Fe.  A typical
sequence is shown in Fig. 2a, with N groups of M pulses.  For the
example, N=6 and M=16.  Fig. 2b shows the output pulses from module 4
if operator 3 reflects enough infrared light to activate it.  The
program tests the signal from the module after each group.  If more
than half of the N groups are detected, the program raises output
control signal 6 to indicate the presence of an operator 3.  This
detection procedure reduces the probability of false triggering by
noise to a negligible value.  Signal 6 may be used to turn on the
display or other equipment.  Visible LED 7 is turned on as an
indicator.

      After signal 6 is raised, the prog...