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Energy optimization of a battery-powered device

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The following describes how the power consumption of a L-Tek FF1502 Bluetooth Low Energy (BLE) beacon was analyzed with ULINKplus. The analysis resulted in an improved software and hardware design that lead to reduced power consumption and longer battery life.

L-Tek FF1052


The L-Tek FF1502 is a Bluetooth Low Energy (BLE) device which operates as a broadcaster, i.e. beacon. Beacons are typically low power devices which sleep most of the time and wake-up for a short period of time to broadcast a message.

The FF1502 is a miniature device (very small form factor) and is powered by a single CR2032 coin cell battery. It is based on the Nordic nRF51822 MCU (Cortex-M0) with an integrated Bluetooth radio and various sensors (temperature, humidity, light, accelerometer, gyroscope, magnetometer) connected via I2C. Sensor data is read periodically and broadcasted via BLE.

The application

During run-time, the application sleeps most of the time with the MCU and all sensors being in low power mode. Every ten seconds, it wakes-up periodically and reads the sensors (temperature, humidity and light). Then, the sensor data is broadcasted via BLE and the device goes back to sleep again.

Analyzing and optimizing sensor I2C software interface

Original software

Problems identified:

Trigger sensors for measurement:

  • Current: 300 µA expected, but 1.5 mA measured.
  • Analysis showed that this was caused by an additional I2C command.

Read sensors in polling mode:

  • Read time expected: 3 ms, but 19 ms measured.
  • Analysis showed that this was caused by the additional I2C command and polling mode.
Optimized software

Results after optimization:

  • Triggering sensors works with lower current
  • Read sensors is faster (less MCU activity)

Analyzing and optimizing the hardware design

Original hardware

Problem identified:

High reverse current through diode D2:

  • Current: nA range expected, 4 µA measured.
  • Exchanged PMEG4005EJ with PMEG6010CEH.
Optimized hardware

Results after optimization:

  • Diode current: 400 nA

Overall 75% less energy consumed.

Battery lifetime

Battery lifetime

The FF1502 runs from a CR2032 battery with a capacity of 230 mAh. The sensor data is sampled every 10 s.

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