SIM800C GSM/GPRS RS232 MODEM (DB9), the latest addition to rhydoLABZ GSM/GPRS modem, helps to add wireless connectivity to your project using RS232 UART interface. It is built with Quad Band GSM/GPRS engine – SIM800C, that works on frequencies 850/ 900/ 1800/ 1900 MHz.You can connect the modem directly to PC as well as microcontroller with RS232 Chip(MAX232). The baud rate is configurable from 9600-115200 through AT command. The GSM/GPRS Modem is having internal TCP/IP stack to enable you to connect with internet via GPRS. 

The Modem is manufactured with Automatic Pick and place machine with high quality standard.The onboard Low dropout 3A Power supply allows you to connect wide range unregulated power supply . Using this modem,you can make audio calls, SMS, Read SMS, attend the incoming calls and internet etc through simple AT commands

  • Make and receive voice calls, Send and receive SMS messages
  • Send and receive GPRS data (TCP/IP, HTTP, etc.)
  • Configurable Baud rate (9600-115200, factory default value: 9600)
  • AT command interface
  • Input Voltage : 5V-12 V
  • Sim card socket
  • Network, Status and Power indication LED’s
  • Network, modem status,CTS/RI and RTS/RF SYNC can be taken via DB9 connector
  • On board SMA connector for GSM antenna
  • Provision for  UFL connector for external antenna
  • Option for audio interface
  • Normal operation temperature: -40 °C to +85 °C
  • Provision for firmware updation.
  • Low power consumption.
  • M39302 linear voltage regulator is used for provides a low-dropout,high-current output
  • Onboard MAX232 IC for level conversion.
  • Power supply voltage is 3.3V~4.4V
  GSM/GPRS Specification



K4:USB Connector

K5:Power Connector

Connect 5V to 12V  from an external power supply .

K7:Speaker and MIC connector

K6:DB9 Female Connector


  • Insert an unlocked SIM card to SIM card Holder. 6 Pin Holder for SIM Cards is provided on the Modem.

  • Close SIM card Holder.Both 1.8 volts and 3.0 volts SIM Cards are supported by SIM800C .the SIM card voltage type is automatically detected.

  • Assemble GSM Antenna to the modem
  • Connect serial cable to the modem.
  • Give power supply in between  5V to 12V through the power jack provided.
  • Default factory Baud rate is 9600.
  • When the modem is successfully powered-up, the PWR LED (RED) on the modem  will be ON, the STS LED (GREEN) will light after 1-2 seconds and the NET LED(BLUE) will blink every second. After the Modem registers in the network (takes between 10-60 seconds), this LED will blink in step of 3 seconds.
 LED Status Description

 The Network LED indicates the various status of GSM module eg. Power on, Network registration & GPRS connectivity. When the modem is powered up, this NETWORK LED will blink every second. After the Modem registers in the network (takes between 10-60 seconds), this LED will blink in step of 3 seconds. At this stage you can start using Modem for your application,showing that modem is registered with the network.

How to Test
Check your GSM/GPRS modem using Terminal software
  • You can directly connect SIM800C GSM/GPRS RS232 modem (DB9) to your PC through serial port, no need of any interfacing modules.
  • If serial port is not there in your PC (some laptops doesn’t have serial port interface) then  you can use USB to serial Adapter(DB9) for this purpose.
  • Once you are done with all these procedures, check appropriate COM port that got assigned to the Communication Port in your system by looking into the device manager like as shown below.

  • Since we are using Hyper Terminal software and select the com port and baud rate(default baud rate 9600) and press OK button.

  • Now let’s try to check our Modem with AT commands for that we need to send following AT commands to Modem as shown  below.

The above shown command :

  • AT command (followed by enter) after “OK” response, this signifies that our Modem is working properly.
  • ATE0 command (followed by enter) is being sent to stop the echo.
  • AT+CREG? (followed by enter) is being used to check whether the SIM got registered or not.
Sending the text message from PC using AT commands .

Now next let’s send a message using SIM800C GSM/GPRS RS232 modem (DB9).For sending message we need to first send related AT commands to initialize the modem to send a message.

  • The AT+CMGF=1 command (followed by enter) sets the GSM Modem in SMS text mode.
  • AT+CMGS=<number>followed by enter gives<CR><write message><CTRL-Z><CR> represents the carriage return character.
    <Ctrl+z>When you finish entering the SMS message body, you have to enter the <Ctrl+z> character to mark the end of the SMS message body.
    +CMGS: x gives OK response; where x = “current number of sent SMS messages”.
Receiving the Text message in Modem and displaying in Hyper terminal.
  • Now let’s receive a message usingSIM800C GSM/GPRS RS232 modem (DB9) .For receiving message we need to first send related AT commands to initialize the modem.

  • AT+CNMI=2,1,0,0,0 command (followed by enter) set the modem to indicate received messages with +CMTI response indicates that new message has been received and shows location number of last received message  in above figure it is shown by number ’20′.
  • AT+CMGR=<index> :<index>integer type; value in the range of location numbers supported by the associated memory and gives +CMGR response which includes status i.e “REC UNREAD” Received unread messages,Sender’s number,date,time and received message.
Receiving a voice call from Modem using AT Commands
  • For receiving call we need headset,connector jack and modem.
  • Headset is connected in the marked pins of GSM Modem
  • For receiving a call  firstly we need to send some AT commands as shown below.

  • Loudspeaker Volume Level
    0..max – the value of max can be read by issuing the Test command
    For example:
    AT+CLVL=100 -Command is used to select the volume of the internal loudspeaker audio
  • RING indicates incoming call.
  • For Attending call we are using ATA command (followed by enter) gives “OK” response when call is connected.
  • For Disconnecting call we are using ATH command  (followed by enter) gives “OK” response when call is disconnected.

Sample code below shows how  we can send a message using Arduino interfacing with modem


Sample code below shows how we can send a message using pic microcontroller interfacing with modem.

 How to Buy



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