Power consumption of autonomous IoT devices

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.

 

System Setup:

In order to determine the energy consumption a simple system setup was used to determine the current at a 12 Volt battery.

Wiring Schema

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.

Components:

Arduino Source Code:

The source code for Arduino IDE 1.6.13 to switch between the four states mentioned above:

Source Code Power Consumption Evaluation

Measurement Results:

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.

Summary:

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.

References:

  • Thanks to the girls and guys from Geeetech for publishing the basic information on how to control the SIM900 board:

http://www.geeetech.com/wiki/index.php/Arduino_GPRS_Shield

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