Written by: Niklas Graniittiaho
I have done research about SIM800L GSM/GPRS module and how to wire it to Arduino UNO. SIM800L is a cellular module which allows GPRS transmission, sending and receiving text messages (SMS) and making and receiving voice calls. You can can connect two antennas to it. First is made of wire (which you solder directly to the module), second antenna yo can connect with IPX connector. This (IPX)antenna has better perfomance than the antenna made of wire. If you use IPX antenna you can put put your module to a metal box, as long as the antenna is outside. SIM800L supplies voltage from 3.4V to 4.4V and recomended voltage is 4V. Module support frequencies 850/950/1800 and 1900 MHz and can work in temprature range from -40 to + 85 ° C,
which is enough to our project.
I found several ways how people have connected SIM800L to Arduino. Roland on teachmemicro.com has used Li-Po (Lithium polymer battery) in his configuration. The battery is connected to GND (ground) pin on Arduino and the other wire from the battery is connected to SIM800L. SIM800L is connected to digital pins 2,3 and 4 on Arduino. This configuration is a closed elecrical circuit.
On exploreembedded.com they have also used Li-Po (Lithium polymer battery) in their configuration, but there is also a NPN transistor and a resistor. The battery is connected to the NPN transistor, which is connectedto the resistor and SIM800L module. The SIM800L module is connected to the battery and digital pins 10 and 11 on Arduino. To me this configuration seems to be too complicated, because SIM800L supports the voltage value (3.7V), which the battery gives. There is no need to change the voltage value with a resistor.
On connectedcities.com they don´t use battery or other components in the middle of connecting SIM800L and Arduino. They have connected SIM800L directly to pins 5V, GND (ground), 1 and 2 on Arduino. Using 5V pin to connect SIM800L
is a bit risky because that is out of supported voltage range and could lead to overheating of SIM800L module. But according to description on this site 5V pin in “Arduino generate current from 500mA -1 Amp which gives a maximum power of 5 Watts.”.
This amount of watts qualifies from recommended power and there is no risk of overheating. For that reason we will probably try this setup in our project. We have two SIM800L modules, so if one will break that wont be a problem.