Evaluation of the power consumption of an autonomous IoT device
The popular Arduino Uno micro-controller in combination with GSM/GPRS shields based on the SIM900 chip are quite popular as prototype platform for new developments or autonomous IoT systems. The main challenge to implement a true energy autonomous system is the considerable energy demand of this components if you use them out-of the-box. Data sheets and other supplier information give no or only limited information of the true power requirements.
An evaluation project from CADEMIS determined the energy requirements of a basic setup which might be a useful indication for the design of related IoT systems.
In order to determine the energy consumption a simple system setup was used to determine the current at a 12 Volt battery.
A control program implemented in the Arduino IDE switches between four different states:
1: GSM board OFF, Onboard LED ON
2: GSM board OFF, Onboard LED OFF
3: GSM board ON, Onboard LED OFF
4: GSM board ON, Onboard LED ON
Between the states a delay of 10 seconds was implemented in order to get a steady reading on the Ampere-meter.
Arduino Source Code:
The source code for Arduino IDE 1.6.13 to switch between the four states mentioned above:
|GSM Shield||LED||Current / mA||Power / mW|
|OFF||ON||54 mA||648 mW|
|OFF||OFF||44 mA||528 mW|
|ON||OFF||68 mA||816 mW|
|ON||ON||80 mA||960 mW|
Special remark on switching on the GSM Shield: When switching on the board (between state 2 and 3) the power consumption is between 70 mA and 220 mA for about 5 seconds. As mentioned in several posts in forums causes every switching operation a significant peak in current and power.
It is strongly recommended to switch off unused loads in order to reduce the power consumption by up almost 50% for a simple setup like this. This can double the operation-time between battery reloading or reduce the solar power requirements and costs.
- Thanks to the girls and guys from Geeetech for publishing the basic information on how to control the SIM900 board: