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Till the time I do not connect my ATmega 644 to serial monitor, Sim 800 doesnt works and once connected and gsm starts to run even if I disconnects ATmega to serial monitor. Can anyone please help? Thanks in advance. To begin, insert a GSM SIM card into the modem and connect it to an available USB port on your computer. A GSM modem could also be a standard GSM mobile phone with the appropriate cable and software driver to connect to a serial port or USB port on your computer.
GSM library
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The text of the Arduino reference is licensed under aCreative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.
With driver-less cars carrying passengers and Trucks carrying valuable cargo, it brings in the need for a Fleet Management system in which we need to track them to know their location and ensure if they are at the right place at the right time. Generally a but here in this tutorial we will use GSM SIM800 module to build a simple Location tracking system with Arduino.
This GPRS tracking system compromises the GSM modem and the microcontroller (Arduino) and is fabricated on a PCB from. It works in such a way that when a phone call is made to the GSM module, the module will check the location and sends it back as a text message with Google map link to the number from which the phone call is made. This link when opened on phone will pin the location of modem on Google Maps. Sounds Interesting enough!!?
So, let’s get started.Circuit Diagram. This GSM car tracker system will use GPRS of SIM800 GSM module which will be connected with a microcontroller like Arduino. Although both the GSM module and the Arduino boards are available as separate packages I decided to make my own circuit combining both of them on a single board to save cost and space. The board can be powered by a 12V adapter or from the 12V battery in the cars/trucks, the on board buck converter will step down the 12V to 4V for GSM module and as 3.3V for the microcontroller to work. The complete circuit diagram is given below. Further below I will split this circuit diagram into blocks and explain them to make sure you can use them or modify them according to your application needs.LM2596 Power moduleWe have used the LM2596 Buck regulator IC to provide 4V to the SIM800 module from the input 12V. The SIM800 module requires around 2A peak current when initialized and searching for network, hence the power supply should be able to source that current, else the module will enter shutdown mode, and hence the LM2596 IC is selected which can supply upto 3A.
The power supply regulator circuit is shown below.The 12V unregulated voltage is provided to pin 1 and the regulated voltage is obtained on pin 2, which is then passed through an LC filter of value 100uH and 470uF respectively to filter output switching noise. The output voltage can be set by using the resistors R30 and R29 forming the potential divider circuit and connected to feedback pin as shown above. The formulae to calculate the output voltage for LM2596 is given below Vout = 1.23. ((R1+R2)/R1)In our case for the above diagram, R29 is R1 and R30 is R2. So I have selected a value of 1k for R29 and 2.2k for R30 to get an output voltage of 4V. Note that the SIM800 module reacquires voltage between 3.7V to 4.2V to operate normally.Powering and Communicating with SIM800 ICThe SIM800 GSM modem is commonly available as modem, but we have used the bare IC package to reduce board space and cost. Using the SIM800 modem is pretty much straight forward, we simply have to power the IC though the VBAT and GND pins and then use the PWR KEY pin to enable the modem by pulling the pin down for 1 second.
By default the pin is pulled high internally to VBAT through a resistor.
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