GSM Based Stepper Motor Control

The speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied... - Kaushal K Jaiswals, Parikshit Kumar, Dr A K Bhardwaj

Stepper motors find lot of applications in computer peripherals, business machines, process control, machine tools and robotics. Especially, in robotics and process control like silicon processing, I.C. Bonding and Laser trimming applications, it is necessary to control the stepper motor from remote places.

This project is to control the stepper motor through GSM MODULE. This deals with the design and development of hardware and software for Wireless Stepper Motor Control System.

This era is an age of machines. Every work – the human do – is being made easy by the use of machines, for example: Robots. There is a very large scale utilisation of robots in industries, and humans are required to only command these robots.

The project deals with the design development of hardware and software for wireless stepper motor. Switches are provided to control the direction of stepper motor on the transmitter side. The status of these switches is transmitted using GSM transmitter and received by the GSM receiver. The microcontroller at the receiving end continuously monitors the status of these switches received from the decoder and performs the corresponding action. And hence the speed of the step movements and the direction can be controlled and varied. For every change required in the step movement of the stepper motor, the current situation value has to be reset to the next value to be acquired after switching off the main power supply. Then the motor has to be restarted for the execution of the next value of the direction and speed of the stepper motor. And all this can be done with the help of GSM MODULE, saving the user the horror of a complicated puzzle of wires, and hence it converts a bizarre difficult technology to an easy and user-friendly one.
16 X 2 Liquid Crystal display (LCD) is provided at the receiver side to display the status of the stepper motor. L293D driver is used to drive the stepper motor. This project uses regulated 5V and 12V, 500mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer.

A stepper motor is an electromechanical device, which converts electrical pulses into discrete mechanical movements. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied to it in the proper sequence.
The motors rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of motor shafts rotation. The speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied.
This project is designed with an idea to use the mobile hand set as a long distance remote controller. The mobile sets are now a days used most widely and very commonly. The SMS can be sent to any mobile user of any service provider with no or a minimum charge. This system is designed using a GSM modem. The GSM modem is configured as a receiver. The SMS sent by the user is written in a particular format. The controller receives the message and decodes it to identify the task to be done.

Fig. 1.1: Block diagram of stepper motor control through GSM module…

The main components of this project: GSM modem, Microcontroller, LCD, L293D and Stepper motor.

GSM module

Fig. 1.2: GSM module…

SIM 900 is a Tri band GSM/GPRS engine that works on frequencies 900MHz, DCS 1800 and 1900MHz. With tiny configuration of 40mmx33mmx2.9mm, SIM 300 can meet almost all the space requirements in your applications, such as smart phone, PDA phone and other mobile devices. The physical interface to the mobile application is a 60 pin board to board connector, which provides all hardware interfaces between the module and customers’ boards except the RF antenna interfaces.


When we have to learn about a new computer, we have to familiarise about the machine capability we are using, and we can do it by studying the internal hardware design (devices architecture), and also to know about the size, number and the size of the registers.
A microcontroller is a single chip that contains the processor (the CPU), non-volatile memory for the program (ROM or flash), volatile memory for input and output (RAM), a clock and an I/O control unit. Also, called a ‘computer on a chip,’ billions of Microcontroller Units (MCUs) are embedded each year in a myriad of products from toys to appliances to automobiles. Eg., a single vehicle can use 70 or more microcontrollers.


LCDs typically have 14 data pins and 2 for the LED backlight. character LCDs use a standard 14-pin interface and those with backlights have 16 pins. There may also be a single backlight pin, with the other connection via ground or VCC pin. The two backlight pins may precede the pin 1.

The nominal backlight voltage is around 4.2V at 25˚C using a VDD 5V capable model. Character LCDs can operate in 4-bit or 8-bit mode. In 4 bit mode, pins 7 through 10 are unused and the entire byte is sent to the screen using pins 11 through 14 by sending 4-bits) at a time.


The L293D is an integrated circuit motor driver that can be used for simultaneous, bi-directional control of two small motors (small means small). The L293D is limited to 600 mA, but in reality can only handle much small currents unless you have done some serious heat sinking to keep the case temperature down. Unsure about whether the L293D will work with your motor? Hook up the circuit and run your motor while keeping your finger on the chip. If it gets too hot to touch, you can’t use it with your motor.

The L293D is a quadruple high-current half-H driver designed to provide bidirectional drive currents of up to 600-mA at voltages from 4.5 V to 36 V. It is designed to drive inductive loads such as relays, solenoids, DC and bipolar stepping motors, as well as other high-current /high-voltage loads in positive-supply applications. All inputs are TTL-compatible. Each output is a complete totem-pole drive circuit with a Darlington transistor as sink and a pseudo-Darlington as a source. Drivers are enabled in pairs with drivers 1 and 2 enabled by 1,2EN and drivers 3 and 4 enabled b3, 4 EN. When enable input is high, the associated drivers are enabled, and their outputs are active and in phase with their inputs. External high-speed output clamp diodes should be used for inductive transient suppression. When the enable input is low, those drivers are disabled, and their outputs are off and in a high-impedance state. With the proper data inputs, each pair of drivers forms a full-H (or bridge) reversible drive suitable for solenoid or motor applications.

Stepper motor

A stepper, or stepping motor converts electronic pulses into proportionate mechanical movement. Each revolution of the stepper motor’s shaft is made up of a series of discrete individual steps. A step is defined as the angular rotation produced by the output shaft each time the motor receives a step pulse. These types of motors are very popular in digital control circuits, such as robotics, because they are ideally suited for receiving digital pulses for step control. Each step causes the shaft to rotate a certain number of degrees.

Fig. 1.3: GSM based stepper motor control…

Result and discussion

Three switches are used to control the direction of the stepper motor at the transmitter side. The status of these switches is transmitted using GSM transmitter and received by the GSM receiver.

The microcontroller at the receiver will be continuously monitoring the status of these switches (received from the decoder) and perform the corresponding action.

The GSM modules used here are STT-434 MHz Transmitter, STR-434 MHz. Receiver, HT640 SMS Encoder and HT648 SMS Decoder. The three switches are interfaced to the GSM transmitter through SMS encoder. The encoder continuously reads the status of the switches, passes the data to the GSM transmitter –and the transmitter transmits the data.
At the receiving end, the GSM receiver receives this data, gives it to SMS decoder. General format of SMS sent is #B1000*, #B1100*, #B1110*, #B1111* for backward movement of motor, and according to vary speed. And general format for forward direction is #F1000*, #F1100*, #F1110*, #F1111* for forward directional rotation and as per
speed required.

This decoder converts the single bit data into 8-bit data, and presents it to the microcontroller. Now, it is the job of the controller to read the data and perform the corresponding action i.e., to rotate the stepper motor clockwise, anticlockwise or entirely stop it.

The idea behind this project is to use the existing GSM infrastructure. So, all the operations involve the GSM system also. As we send any SMS, it goes through the GSM system. Any sent SMS can be received, if we use a SIM card and SSM module.

To operate any GSM modem, we have to use the AT commands to operate them. For example, if any SMS arrives, the GSM modem sends the serial data in ASCII format. We can read these data, if we connect the modem with the serial port of the microcontroller at the baud rate of 9600.

As the microcontroller comes to know that an SMS has arrived, it can send proper AT command to read the SMS. The reading of SMS returns the mobile no of sender, the time and much more information. We have to select the SMS part of the message. The starting string of the SMS is used as the password. As the password is matched, then the SMS arrival is assumed to be valid by the microcontroller. Otherwise, it ignores the SMS. Following the SMS, the microcontroller directs the motor driver, which in turn drives the motor. The advantages of SMS based control are:

This is cheaper. The SMS can be retained in the network even though the network is busy for some time.
The SMS can be written through Internet without any cost.

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