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FlexSense™ Power Management

Overview

In this article:

One of the key benefits of FlexSense is its ultra-low power design, enabling years of lifetime on two or four AA Lithium batteries. However, verifying that your firmware is behaving as expected and allowing the FlexSense to enter its low-power modes requires measuring current draw directly.

This section guides you through using a Nordic Power Profiler Kit II (PPK2) to observe the actual power profile of your FlexSense firmware and verify that the device enters low-power sleep between jobs.

This guide focuses on the PPK2, but many alternatives to the PPK2 exist and can be used for this application. The PPK2 is cost-effective, but it is not the most accurate option on the market. It is also perfectly possible to use a good multimeter for this as well, it might not have the same precision and dynamic response to the current consumption changes, but it is enough to have a good idea if the low-power sleep is being achieved, for example.
The FlexSense must not be connected to both USB and PPK simultaneously, as only one power source can be connected at a time.

Required Equipment

How to Measure Current Draw

The idea is that the PPK2 provides power to the FlexSense, while measuring the current.

Recommended Part List

We recommend the following parts for probing the battery terminals.

Description Manufacturer Part number
Clamp-type test probe with 4mm banana plug socket - black Hirschmann Test & Measurement 930113100
Clamp-type test probe with 4mm banana plug socket - red Hirschmann Test & Measurement 930113101
Test lead with 4mm banana plug to 0.64mm square pin socket- black Hirschmann Test & Measurement 934160100
Test lead with 4mm banana plug to 0.64mm square pin socket- red  Hirschmann Test & Measurement 934160101

Wiring Diagram

Below are the steps to connect the FlexSense to the PPK2:

  1. Insert the banana plug from the red test lead into the red banana-plug socket on the clamp probe.

  2. Insert the banana plug from the black test lead into the black banana-plug socket on the clamp probe.

  3. Insert the female square pin from the red test lead into the VOUT terminal on the PPK2.

  4. Insert the female square pin from the black test lead into the GND terminal on the PPK2.

  5. With the FlexSense’s USB-C port facing upward, attach the grip jaws from the red clamp probe to the left battery terminal inside the FlexSense.

  6. With the FlexSense’s USB-C port facing upward, attach the grip jaws from the black clamp probe to the right battery terminal inside the FlexSense.

The following wiring diagram illustrates this connection.

Wiring Diagram
Double-check polarity. Reversed polarity may damage your FlexSense device.
Improper probing may damage battery terminals and void the product warranty.

Measuring

  1. Connect the FlexSense battery terminals to the PPK2.
  2. Connect the PPK2 to the PC, Launch nRF Connect for Desktop and Open the Power Profiler app.
  3. Select your PPK2 and set the Power Supply Mode to Source Meter
  4. Set the source voltage to 3600mV (to emulate L91 lithium cells) and enable the power output.
  5. Set the sampling to 100,000 samples per second, which is set to sample forever.
  6. Click Start

Expected Current Profile

State Current (typical) Description Duration
Soft Off 1µA - 2 µA This is the current expected when the FlexSense is powered, but the button has not been pressed for the first time Until the button is pressed
Wake Up and GNSS Fix 5mA - 2A The device is executing its boot procedure and acquiring a GNSS fix 90s to 120s
BLE Advertising 0.5mA - 2mA The BLE is advertising, and the device can be connected to in the FlexAssist Mobile App 60s
Sleep less than 10µA The FlexSense is in Low Power mode Until next Job

Troubleshooting High Sleep Current

Symptom Likely Cause Potential Fix
Sleep current greater than 10 µA GPIO or peripheral leakage Confirm that where Init API functions were used, De-Init functions were called before a job is finished.
Sleep current greater than 100µA BLE advertising not switched off Confirm that no devices are connected to the FlexSense via Bluetooth, as this will keep the BLE on.
Sleep current never below 1mA The Device is not entering Sleep mode Confirm that there are no loops or functions in your user application that will keep a job from ending and allowing the system to enter Sleep mode.

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