Communications and Network, 2013, 5, 25-28
doi:10.4236/cn.2013.51B007 Published Online February 2013 (http://www.scirp.org/journal/cn)
A Smart Home System Design Based on GSM
Rongrong Zhang, Xiaoping Zou, Wenhui Huang, Qimu-Surong
Beijing Key Laboratory for Sensor, Beijing Information Science and Technology University, Beijing, China
Received 2012
ABSTRACT
This paper introduces a mobile phone short message control method in smart home based on GSM (Global System for
Mobile communications). AT commands and the system structure is illustrated in detail. The hardware system including
STC89C51 and TC35i is presented. The software framework is also analyzed clearly in this paper. In addition, some
other potential application areas and its direction of development in future are given at last.
Keywords: GSM; Smart Home; STC89C51; Wireless Communication
1. Introduction
As the prevailing trend of IOT (Internet of Things) [1]
covering the glob al, smart home find its way in the trend.
All control and communication method dashed into this
area: GSM, WIFI, CAN, Bluetooth, ZigBee. They all try
to solve those problems in this smart world [2]. Among
these solutions, GSM has a prominent po sition as mobile
phone has been a comprehensive communicating fashion
in modern society.
GSM is a kind of digital mobile communication net-
work. It is developing rapidly in recent years. And the
short message service is an important business network
based on GSM. Its simple and efficient performance as
well as relatively low fee absorbs the customers. [3]
Moreover, the technical possibility for many types of
remote monitoring make it bound to be the most conven-
ient and welcomed way in smart home control as people
can monitor their home anytime anywhere. In this paper,
I’ll present you a wonderful smart home solution based
on GSM and explain the implementation of software and
hardware.
2. System Framework
The GSM control system contains the communication
part, the control center and the object to be controlled.
Figure 1 is the system block diagram.
In this system, GSM module plays the communication
role. STC89C516RD+ bears the task of a control center.
The relay module connected to home appliances is the
object to be controlled. There are several channels of
relays on the module. Each connects to a different home
appliance.
The GSM module with a smart card is responsible for
receiving text messages from the GSM network and
transmitting the short message from the local MCU
(STC89C516RD+) to the GSM network. It also receives
message command from user’s mobile and sends the cor-
responding command to the control center STC89C-
516RD+. The controller analysis the command and con-
ducts the relay to open or close the anticipated cannel,
such to open or close the related appliance. After this, the
control center indicates the GSM module to send feed-
back message to the user terminal.
3. AT Commands
MCU communicate with GSM module through AT (At-
tention Commands) [4]. AT command set is the interface
standard between TE (terminal equipment) and TA (ter-
minal adaptor), as well as between DTE (data terminal
equipment) and DCE (data circuit terminal equipment).
In the early 1990s, AT command set is only used in the
operation of modem. With a series of evolution, AT
commands are added GSM07.05 standards. Up to now,
Most of the GSM modules support this standard.
3.1. The Syntax of Basic AT Commands
Each AT command must begin with “AT” or “at”, and
end with <CR>. Four kinds of syntax are showed in Ta -
ble l.
Figure 1. The block diagram of the mobile control system.

R. R. ZHANG ET AL.
26
3.2. General AT Commands
The AT commands used in this remote control system
are shown in Table 2. [5]
4. Hardware Structure
Figure 2 is the picture of the mobile phone control sys-
tem. As show ed in th e p ictur e, th ere are two bo ards and a
GSM module in the system. The board above is the relay
module and the bellow one is a control center board with
STC89C516RD+ on it. The GSM module is connected to
the center board through a pair of UART ports of
STC89C516RD+ controller. Figure 3 is the hardware
structure of the system.
Table 1. Basic AT commands syntax.
The Type of
Instruction The Syntax of Command The Describe of Instruction
Test Command AT+CXXX=?
Test the implementation
status of the command,
and return parameters and
parameter rang e
Read Command AT+CXXX? Return the current value of
parameters
Write Command AT+CXXX=<...> Set the user-defined value
of parameters
Execute Command AT+CXXX Execute the command
Table 2. General AT commands.
AT+CMGD Delete SMS message
AT+CMGF Select SMS message format
AT+CMGR Read SMS message
AT+CMGS Send SMS message
AT+CNMI New SMS message indications
TC35I module exchanges data with user terminal
through the GSM network. STC89C516RD+ transfers
data with TC35I module through RXD port and TXD
port. It controls the relay module through I/O ports. Each
port corresponds to a relay and each relay links a home
appliance.
Figure 4 is the schematic of the GSM module and
MCU. Figure 5 is the PCB of the main board of the sys-
tem, which is designed by Altium Designer.
Figure 2. The picture of the mobile control system.
Figure 3. The hardware structure of the system.
Figure 4. The schematic of the GSM module and MCU.

R. R. ZHANG ET AL. 27
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Figure 5. The PCB of the main board of the system.
The central part of the system comprises of a GSM
module and a MCU. We adopt modem TC35I of SIE-
MENS as the GSM module. The TC35I module can
work at frequencies of EGSM900 and GSMl800 and can
transmit sound, data, message and fax. Its work voltage
can reach 8V-30V except for data transmission period
when the work voltage is 5.6V-30V, and it supports
GSMphase2/2+ and AT instructions [5]. Moreov er, it has
a whole SIM reader card, a RS-232 interface and other
standard industrial interface.
We adopt STC89C516RD+ of ETC as the MCU,
which has features of ultra low work voltage, ultra small
scale power consumption, 63K-Byte FLASH, 1280-Byte
RAM, watchdog, double-speed, lower EMI, timer, ISP,
IAP, and asynchronous serial communication interface
UART. The MCU set the value of I/O ports according to
the received short massages, so as to control the status of
the relays.
5. Software Framework
System software has two functional components: SMS
(Short Message Service) sending & receiving part and
SMS parsing & execution part. The function of sending
& receiving is completed by GSM module which is
mainly responsible for receiving remote control com-
mands and returning the status and data of the system to
remote control terminals; the control section is completed
by the MCU, which will parse the received GSM com-
mands so as to control the corresponding peripherals.
TC35I communicates with STC89C516RD+ though
serial port. Figure 6 is the main flow chat of control al-
gorithm on the MCU.
The program is compiled in the KEIL uVision3 build
environment based on AT command set. The process is:
Step1: Initialize serial port, mainly to operate serial
port registers in KEIL build environment including timer
register, baud rate register, serial port receive register and
interrupt flag configur ation. The purpose is to prepare for
the data transfer between the GSM module and serial
port.
Figure 6. The program flow chart of the MCU.
Step2: Initialize GSM module. A low level pulse
should be given to its IGT pin. At least 100ms low level
pulse is needed to start the module. The fall time of the
signal is less than 1ms. After start, the IGT pin should
stay in high level. All these level shifting and keeping is
managed by software.
Step3: Confirm whether the GSM module has suc-
cessful initialized. If not, check the hardware connection
and correction of the program. If success, the GSM mod-
ule can communicate with the MCU. After entering the
main loop, the MCU waits for messages coming. If there
is message coming, it has to receive the message and
confirm whether the message has been received entirely
until the whole message is received .
Step4: Parse the message command. If successfully
parsed, the MCU will send corresponding control com-
mands to the related device. If failed parsing, it will re-
turn error message to the GSM module.
Step5: Return the parse and control result to qualified
user terminal in the feedback message.
Step6: The program goes to the next round of cycle
and waits the next message coming.

R. R. ZHANG ET AL.
28
6. Software Tests and Results Discussion
The qualified mobile phone can send prescriptive text
messages remotely to control the work status of home
appliances. When we edit a message “open1” and send to
the SIM card number of the GSM module, the light on
channel1 is illuminated. Then we receive a feedback
message from the system indicating “Light 1 opened!”
When we send a message “close1” to the system, the
light will be extinguished and a feedback message is send
to the mobile phone. If we use other commands (pre-
scribed in the program) like “open2”, “open3”…other
appliance will be opened. In this way, we realize the
function to control home appliances at any place the
GSM networ k cov ered.
7. Conclusions and Prospect
This system makes remote control available based on
GSM with low cost hardware and low consumption. The
design is not merely a good smart home solution. It
makes sense in industry control and other fields. Al-
though it’s a simple solution, it indicates the technology
trend of smart world. In our future research, more tech-
nology will be added to the system. For example, sensor
module, which can collect parameters like temperature
and humidity as references for relevant appliance con-
trolling.
With the fast development of mobile phone hardware
and software, embedding accessional software in mobile
phone will be possible as mobile p hone tends to be like a
mini computer. In the near future, we can monitor and
control our home appliances through the multimedia ap-
plication software on our mobile phone. There will be
video, sound or word messages interact with smart home
devices [1]. The prospect of mobile phone control system
is bright with no doubt.
8. Acknowledgements
This work has been partially funded by the Program of
Beijing Key Lab for Sensor under Grant No.KF2011
1077205.
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