AUTOMATIC ROOM LIGHT INTENSITY DETECTION AND CONTROL USING A
MICROPROCESSOR AND LIGHT SENSORS
Ying-Wen Bai and Yi-Te Ku
Department of Electronic Engineering, Fu Jen Catholic University
Taipei, Taiwan, 24205, R.O.C.
E-mail: bai@ee.fju.edu.tw
ABSTRACT
In this paper we propose a design using both a
microprocessor and light sensors for automatic room light
detection and control. Our design, the HLCM (Home Light
Control Module) which will be installed in every light
fixture of a family, is made up of four blocks: the
pyroelectric infrared (PIR) sensor circuit, the light sensor
circuit, the microprocessor and the RF module. By using the
PIR sensor circuit, the HLCM detects if a human body
enters the detection area or not. If there is no human body
present, all controlled lights are turned off. If there is, the
HLCM detects the light intensity under the environment and
maintains sufficient light by controlling the number of lights.
We have also integrated an RF module to transmit and
receive the data from each HLCM so we can control
different lights in different regions. The result of using the
HLCM shows that the total power consumption can be
reduced.
Index Terms — Light Control, Microcontroller,
Pyroelectric Detectors, Illumination Measurement
1. INTRODUCTION
In recent years the energy crisis has become one problem
which the whole world must confront. Home power
consumption makes up the largest part of energy
consumption in the world. In particular, the power
consumption of lamps in a typical home is a factor which
can’t be ignored. The typical user needs different light
intensities in different places. Sometimes the light intensity
from outside is sufficient for the user, and thus we don’t
need to turn on any light. But sometimes the user leaves but
forgets to turn off the light. These factors cause energy
waste. Therefore some power management of light control
in a home is necessary in order to save energy.
Lights are usually controlled by on/off switches. Of
course, the user can switch a light on or off remotely by
connecting a specific device to a PC [1-4], but there has to
be at least a PC, consuming a rather large amount of power
24 hours a day, for the control mechanism. Moreover, this
inconvenient practice comes at a high cost for the user. In
some designs one must install specific hardware and
software to control the lights, resulting in unacceptable costs.
Furthermore this type of system cannot detect either the
temperature of the human body or the room light intensity
[5-8].
In this paper we propose a design for automatic room
light detection and control. As shown in Fig. 1, we install a
low-power HLCM in every lamp in a typical home. The
design detects whether someone is passing through the
detection area not only by means of the PIR sensor in the
HLCM but also by detecting the change of light intensity in
a room by means of the light sensor in the HLCM. We also
use the RF module to communicate among the HLCM to
pre-control the lights. For example, when the room light
intensity is not sufficient, all lights controlled by HLCM A
are turned on. HLCM A will then send a signal to the
nearby HLCM B to turn on a light controlled by HLCM B
in order to increase the light intensity. Moreover, if
someone goes from the kitchen to the living room, the
HLCM in the kitchen notifies the HLCM in the living room
to turn on the light in advance. By using our design one can
achieve high efficiency in home power management.
This paper is organized as follows. In Section 2 the
HLCM is introduced. In Section 3 the light control in our
design is presented. In Section 4 the implementation results
are summarized. In Section 5 our conclusions are presented.
HLCM
RF
HLCM
RF
HLCM
RF
HLCM
RF
RF
HLCM
RF
HLCM
RF
HLCM
Fig. 1 Room light intensity detection and control
architecture
and switching lights on/off by controlling the solid state
relays (SSR) on/off.
2. DESIGN OF THE HLCM
……
……
The HLCM shown in Fig. 2 is made up of the PIR sensor
circuit, the light sensor circuit, the RF module and the lowpower MCU. We also provide a DC power supply from AC
power to every component.
Fig. 2 The circuit diagram of the HLCM
We use the PIR sensor circuit to detect whether someone
is passing through the detection area or not. If a human
body enters the detection area, the PIR sensor receives the
variations of the temperature made by the infrared energy
emitted to the surroundings, and it necessary produces the
variations of electric changes by means of a pyroelectric
effect. Because the electric charges are very few and not
easily sensed by the sensor, we adopt the high-impedance
FET to pick up the signal. Since the output amplitude of the
sensors we measure, about the level of mV, is too small and
not large enough for an MCU, we have to amplify the
output signal from the sensor with a sufficient quantity of
two-stage high-gain amplifiers. Nevertheless, if the gain is
very high, most tiny noises are amplified simultaneously
and interfere seriously with the output signal. Therefore, in
our design we have adjusted the value of both the resistance
and capacitance so as not only to amplify the sensed signal
and but also to restrain any noise resulting from the
temperature variations.
The RF module is specifically designed to connect to the
MCU, thus allowing communication to be made among the
HLCMs. The modulation of the RF communication is FSK,
and the FM modulator works at 2.4GHz frequency and
2MKbps speed. The advantages of RF communication are
the absence of extra connection wires and its low cost.
We have used SSR to switch each light. SSRs have been
utilized to replace mechanical relays because of their many
advantages, like miniaturized configuration, little or no
contact bounce, low energy consumption, decreased
electrical noise, compatibility with digital circuitry and
high-speed switching performance. These SSR also provide
isolation between a control circuit and a switched circuit.
The MCU in the HLCM has three functions as shown in
Fig. 3: to support sufficient light intensity by ascertaining in
which room the user is located, detecting the human body,
Fig. 3 The control flowchart of the microprocessor
3. DESIGN OF THE HLCM
3.1. Light controlled by a HLCM
As shown in Fig. 4, we install an HLCM at each light. The
HLCM detects if a human body is present or not and it
detects the light intensity; it switches each light on/off by
controlling the SSR on/off to support sufficient light
intensity.
Fig. 4 Light controlled by an HLCM
The HLCM measures the average light intensity
supported by a light, which is 170 Lux, and the power
consumption of a light, which is 80 Watts. When a user
turns on all lights, the power consumption increases to 400
Watts. Because there are different levels of sufficient light
intensity in different places, the number of lights switched
on is different. In Table 1 we give examples from three
different places.
Table 1 Power saving in different places
Room
Sufficient light
intensity
Number of lights
switched on by
HLCM
Power consumption
Power saving
Power saving (%)
Living room
Bathroom
Study room
150 Lux
200 Lux
500 Lux
1
2
3
80 Watts
320 Watts
80%
160 Watts
240 Watts
60%
240 Watts
160 Watts
40%
measured by the HLCM to make it similar to that measured
by the digital light meter, as shown in Fig. 7.
3.2 The Communication among HLCMs
As shown in Fig. 5, we use the RF module to transmit and
receive the data from each HLCM in order to pre-control
the lights and support sufficient light intensity. If the light
intensity sources is not sufficient for the user when the all
lights controlled by HLCM A are turned on, the HLCM A
will ask the nearest HLCM B to turn on a light controlled by
HLCM B to increase the light intensity. Pre-control means
that if someone goes from the kitchen to the living room, the
HLCM in the kitchen notifies the HLCM in the living room
to turn on the light in advance. The communication format
has four parts: the address of the HLCM (24 bits), the
address of the light devices (5 bits), the status of light (3 bits)
and the CRC (Cyclic Redundancy Check, 8 bits).
Fig. 6 Picture of an HLCM
Table 2 The average power consumption of the HLCM
module
33
123
68
Operation
Voltage
(V)
3
5
5
Average Power
Consumption
(W)
0.099
0.615
0.34
35
5
0.175
38
5
Average
Current (mA)
Item
RF
MCU
Relay
Body
Detection
Light
Detection
Total
0.19
297
1.419
Value measured by our design
Value measured by digital light meter
3000
Fig. 5 The message format for light control
Illumination (Lux)
2500
2000
1500
1000
500
4. RESULTS OF THE EXPERIMENT
0
0
Fig. 6 shows the implementation of the HLCM. The
hardware prototype circuit of the HLCM is now
implemented on an 8 cm × 6 cm printed circuit board
(excluding the SSR).
The power consumed by the HLCM can be measured
and calculated as shown in Table 2.
We compare the change of the value of light intensity
under the same environment between that measured by our
design and the traditional design measured by a digital light
meter. We place a digital light meter 200 cm below a light.
Because the HLCM is adjacent to the light, as the light
intensity measured by an HLCM is higher than that
measured by a digital meter, we have to adjust the value
120
240
360
480
600
720
Time (Minutes)
Fig. 7 Comparison of the light intensity measured by our
design and that measured by a digital light meter
As shown in Fig. 8, we measure the variations of light
intensity of three modes for a long time under the same
environment. The three modes are the change of light
intensity in nature, the change of light intensity when we
switch the light on/off by ourselves and the change of light
intensity when we install the HLCM at the light. In our
experiment we observe the light intensity when in user time;
we do not observe the light intensity when in non-user time.
Under natural conditions the room light intensity changes
along with the outside environment. When we do the
switching by ourselves there is one condition: When we
switch all lights on because the environment is too dark or
when we do not switch the lights off when just leaving for a
short time, we maintain enough light intensity. When we
switch the lights on/off by using the HLCM, the light
intensity is the same as under natural conditions and it is
maintained at over 500 Lux if there a user. When the user
leaves the room or the light intensity is more than 1000 Lux,
the light is turned off.
The change of light intensity in nature
The change of light intensity when we switch the lights on/off by ourselves
The change of light intensity when we install the HLCM at the light
2500
Illumination (Lux)
Sunny
Cloudy
Partly cloudy
2000
1500
Table 3 Comparison of our design with others
Light Control Design
Home Server
Power Consumption
Body Temperature
Detection
Light Control
Cost
Setup
Pre-control
Light Intensity
Support
Design 1
Needed
120 Watts
Design 2
Needed
25 Watts
Our Design
Not Needed
<1.5 Watts
No
No
Yes
No
High
Complicated
No
No
No
High
Easy
No
No
Yes
Low
Easy
Yes
Yes
1000
REFERENCES
500
0
0
User
time
720
Non-user
time
1440
User
time
2160
Non-user
time
2880
User
time
Non-user
time
3600
4320
Time (Minutes)
Fig. 8 The change of room light intensity under three modes
In Fig. 9 we have compared the power consumption
between switching the lights on/off by ourselves and using
the HLCM. Our measurement confirms that energy is saved
by using the HLCM.
Power consumption (Watts)
potential of the features of low cost, small size, low power
consumption and power saving has been shown.
Table 3, a comparison of designs, shows that our design
consumes less power, and at a low cost. As a result, our
design is better than others because it has more integrated
functions.
Sunny
250
Cloudy
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Switching the lights on/off by ourselves
Switching the lights on/off by using the HLCM
300
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Partly cloudy
200
150
100
50
0
0
720
1440
2160
2880
3600
4320
Time (Minutes)
Fig. 9 Comparison of the power consumption of our design
with that of other designs
5. CONCLUSIONS
In this paper we have proposed a design for automatic room
light detection and control. We install an HLCM at every
light of a family for home power management. The HLCM
detects if a human body is present or not by using the PIR
sensor circuit. If there is no human body present, all lights
are turned off. If there is, the HLCM then detects the light
intensity under the environment by using the light sensor
circuit and the system maintains sufficient room light by
switching lights on/off. To realize light intensity support
and light pre-control, the RF technology for light power
management has been integrated. Consequently, the
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