![]() ![]() The voltage of Li-Po or Li-Ion batteries are too low and change a lot depending on their charge. If we want to use batteries to power the system, this voltage is a bit tricky. We see that the perfect operating voltage for all components is around 4V, as it fits the range of SIM800L as well as the ATmega328P. Good for our power reduction goals! This table from the ATmega218P data sheet shows the potential for power savings by reducing the voltage and frequency. This not only makes it compatible to the SIM800L, it also saves a noticable amount of energy, because the ATmega328P uses less energy with it’s internal 8Mhz oscillator, as well as with lower voltage. Luckily you can use the ATmega328P outside of an Arduino and step down it’s frequency from 16Mhz to 8Mhz. ![]() It also won’t run with 3,3V microcontrollers. While the SIM800L GSM Modem runs on 3,7 to 4,2V, an Arduino normally runs at 5V which makes it incompatible with the module. Receive and make calls using the speaker and microphone outputs I achieved a current draw of around 7mAh in standby. In my project it was especially important for me to keep the power consumption down to an absolute minimum so that the system can run on batteries for months. In this tutorial I’ll share my findings with the hardware and software, as well as power saving tips – that should make it easy for you to build your own setup. ![]() For example for remote sensor data, or remote human interaction via SMS – one of the few protocols which is still present and accessable nearly everywhere in the world. I can think of many use cases for a low power device which is controllable via SMS. I enjoyed the project, but the handling and communication of the different components needed some extra tinkering, which took me some time to figure out. I recently built an SMS chat bot from scratch. ![]()
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