GSM or SIM modules are widely utilized in Internet of Things (IoT) projects due to their capability to transmit & receive data with limited dependencies compared to Wi-Fi & Zigbee. GSM modules offer reliable and long-range communication, requiring only a single SIM card with an active plan. Despite the limitation of not being able to transfer large amounts of sensor-generated data, GSM modules are ideal for different procedures that require transmitting modest amounts of information.
In our tutorial, we will demonstrate how to connect a GSM module to an STM32F103C8 GSM Module microcontroller to send & receive messages from a specified cellular phone number. A 16×2 LCD screen will be utilized to display both incoming and outgoing messages, and two buttons will be incorporated to initiate the sending & receiving of messages upon pressing.
Many projects use GSM technology and connect it to different types of controllers. You may explore these projects by visiting a website and seeing how they were made. You can even try making your own by looking at tutorials that show how to use different types of GSM modules, like SIM900, SIM900A & SIM800.
SIM800C GSM Module
The SIM800C Module is a popular GSM unit with a serial modem and operates within a voltage range of 3.4V to 4.4V. It is designed for use in projects where transfer of data is needed and can connect to four different frequencies. The SIM800C can make and receive calls and send and receive text messages with low energy consumption. It is controlled using special AT commands and can only support one card of SIM. The module has special pins for communication (TX and RX) and can connect to different microcontrollers using the RS232 serial protocol.
Powering SIM800C Module
A 12V Direct Voltage or Direct Current power adapter powers the SIM800C module GSM.
Insert SIM
You insert a card of SIM into the back side of the SIM800C module GSM. Remember that this module does not work with 4G SIM cards, so only use a regular card SIM.
Interfacing SIM800C Module with STM32F103C8 Module
To connect the SIM800C to the STM32F103C8 microcontroller, we will use the UART port, a unique communication tool built into the STM32F103C8. The pins of UART on the STM32F103C8 are labeled as A9 & A10, as shown in the image. The STM32F103C8 Module has 3 UART interfaces that can be used to connect to three different external devices that use serial communication.
Programming STM32F103C8 Module Microcontroller for interfacing
The ARDUINO software can be useful to write code for the STM32F103C8 microcontroller. In our tutorial, you do not need an exceptional programmer like FTDI/ST-LINK. To upload the code, connect the micro USB port on the STM32 to your computer using a USB cable, and then you can start writing the code in ARDUINO IDE. Before writing the code, you need to add the required libraries for the peripherals used in this tutorial and define the pin configuration for the LCD.
Next, initialize the LCD (Liquid Crystal Display)by selecting LCD to begin(16,2), where the parameters specify the type of LCD, which is a 16×2 block. To check if the LCD is properly interfaced and producing output, print a debug message.
Set the direction for the push button data as input mode and define the corresponding PIN.
Pick a speed for sending information through a serial connection.
The code contains two functions, one for sending messages and the other for receiving messages.
· Send Message
This function helps you send text messages to a phone number. First, a special command called AT is propel to the GSM module to tell it you want to send a message and what number to send it to.
Then, another command called AT+CMGS is sent to the module through a port called serial1, and this command tells the module to actually send the message to the specified number.
To send messages, the special command “AT” is sent every second. After sending the message, another command called “CTRL+Z” must be sent to the GSM module through a port called Serial1. This will cause a unique code to be sent to the GSM module.
Once the message is sent successfully, a message saying “SMS sent” will appear on a screen called a 16X2 LCD.
· Receive Message
This function utilizes the AT command to receive and display live messages on the LCD screen.
When you get a text message, it has some information like the time and date. The message is found after the sixth quotation mark (“). The rest of the text is the message you received.
How to Send & Receive Text Messages using STM32 Module?
1. For sending a text message, push the button on left side. The message will be drive to the phone number specified in the system.
2. For getting a text message, push the button on right side. The message will appear on the screen. That’s how you use a GSM module and an STM32F103C8 microcontroller together. If you have any questions or ideas, please let us know by leaving a comment.
Features of SIM800C GSM MODULE
This tiny module is only 1 inch square, but it has many features packed into its small size. Here are some of them:
- Works with four frequency bands: GSM850, EGSM900, DCS1800, and PCS1900.
- Connect to any global 2G GSM network using any 2G SIM card
- Create and answer voice calls utilizing an external 8Ω speaker and an electret microphone.
- Send & receive SMS
- Send & receive GPRS information
- Scan & receive FM broadcasts
