Light Control System
2005. All rights
It is easy to
install a couple of infrared emitter and receiver at
the entrance of your room and maybe you connect them to the
light, but you cannot control the light in this way! You will
never know how many person inside and if the room is empty or
not. In this system, every thing is under control, because it
is smart enough to know how many persons inside; and it can
identify the direction of them, so the light will be turned
OFF when the room is unoccupied; and ON otherwise! This
tutorial will show you how.
shown in Figure 1, Light Control System has five units:
Power supply to convert 240V
AC into 5V DC.
2- Sensing units that convert
body motion into analogue electrical signals.
3- Analogue comparator to convert
analogue signals into digital signals.
4- Microcontroller to process these
digital signals and send the appropriate command to the room
5- Relay to act as an interface between low voltage
(control system and sensors) & high voltage (room
Sensing unit consists of infrared emitter OP295 to produce the infrared beam, & two detectors in
front of the emitter to detect the infrared beam OP598. Since the main idea in
this device is to know person direction; and so, to get this
approach, we have to use tow pieces of infrared detector in
|If you have a camcorder, or just a camera
mobile phone, you can see the infrared light! Just point
the infrared emitter at the camera then you will be able
to see the infrared light in the viewfinder. If you
point your remote at the camera and push a button, you
will see flashing light!|
direction of the person as shown in Fig 2.
Infrared beam become broken due to any body, the output
signals from these detectors will be changed in unique
sequence. Controller will identify the direction of the person
by analyzing these signals as shown in the table at right
"from 1 to 5 passed IN, 5 to 1 passed
Since detectors output signals are
analogue while the controller can only process digital
signals, these signals must be converted to digital through
the analogue comparator LM393.
Controller will increase the
number of the persons in side the room by one, or decrease it
by one when the appropriate sequence of signals have occurred.
If this number is greater than zero, light will be turned on
otherwise it turned off.
After this, controller will stop
scan sensors for one second to allow the whole body to pass.
Fig 3 describe the whole algorithm
Sensors circuit is
so sensitive in Light Control System, that mean any external
noise or any small variation in voltage will change the
sensors circuit status. While these signals are changing due
to these reasons, microcontroller will assume that some one
pass in front of sensor and so a fault will occur. In order to
solve this problem I have used soft and hard components
"capacitors" to make Light Control System stable as much as
possible. A soft component is an algorithm in the control code
to separate the noises signals from the real
have to isolate detectors from any kind of light, except the
- Use TIP110 to drive relay
current; it has Base-Emitter Shunt Resistors built
in. Diode D1 is acting as a freewheeling diode.
reference voltage should be less than voltage produced by the
detectors; otherwise, the system will not function properly .
"Less than 0.1V is recommended"
- The maximum speed of the
body to be detected by the Light control System
is 1.67 meter\second = 0.462 Km\Hour this value is accurate
only if the depth of the passing body in front of sensors is
equal to the distance between these two infrared receiver, if
this depth is more, the maximum speed will be increased.
Light Control System is unable to detect any body with a depth
less than the distance between 2 receiver.
- By adding an
auxiliary switch, Light Control System can be disabled if any
failure has occurred after installing. This auxiliary switch
disables the functionality of Light Control System and
restores the wall light switch to the previous state as shown
in figure 4.