Simblee Concepts

Contributors: SFUptownMaker

Low Power Modes

As a Bluetooth Low Energy device, one of the main benefits of the Simblee module is a long battery life. Under normal circumstances, the module draws about 5mA. This will drain one of our [CR2032 coin cell batteries] in around two days' time.

There are two lower power modes available, however: Ultra Low Power mode, and Off. They differ in how the processor can be awakened and in how much power the processor consumes in that mode.

In ULP mode, the processor consumes about 1/10 the current it does running normally. It can be told to awaken after a specific amount of time or on an event (a rising or falling edge) on a specified pin. The improvement in battery life depends, of course, on how often the processor is awakened; wake it too often and remain awake too long and you may notice very little improvement at all.

In Off mode, the processor consumes about 1/5000 the current it normally does. In this mode, only a pin change event can wake the processor, and it can only execute code within a specially created callback function. However, with current consumption this low, the shelf life of the battery becomes a serious consideration when calculating the total battery life.

Here's the complete listing of the code; it can be downloaded from the GitHub repository directly or from Github as a zip file.

language:c
/****************************************************************************
 * Low Power Example Sketch
 * Low_Power.ino
 * 29 Jan 2016 
 * https://github.com/sparkfun/Simblee_Tutorials
 *
 * This app is a way to show how the Simblee Low Power modes can be used.
 * 
 * Resources: Please install the Simblee support files before attempting to use
 * this sketch; see
 * https://learn.sparkfun.com/tutorials/simblee-concepts#setting-up-arduino for
 * details.
 * 
 * Development environment specifics: Arduino.cc IDE v1.6.7
 * 
 * This code is beerware; if you see me (or any other SparkFun employee) at the
 * local, and you've found our code helpful, please buy us a round!
 * ****************************************************************************/

// To use the SimbleeForMobile library, you must include this file at the top
// of your sketch. **DO NOT** include the SimbleeBLE.h file, as it will cause
// the library to silently break.
#include <SimbleeForMobile.h>

const int led = 2; // The Simblee BOB (WRL-13632) has an LED on pin 2.
int ledState = LOW;
const int button = 3;

void setup() 
{
  pinMode(led, OUTPUT);
  digitalWrite(led, ledState);
  pinMode(button, INPUT_PULLUP);

  // advertisementData shows up in the app as a line under deviceName. Note
  // that the length of these two fields combined must be less than 16
  // characters!
  SimbleeForMobile.advertisementData = "LoPow";
  SimbleeForMobile.deviceName = "WRL-13632";

  // txPowerLevel can be any multiple of 4 between -20 and +4, inclusive. The
  // default value is +4; at -20 range is only a few feet.
  SimbleeForMobile.txPowerLevel = -4;


  // This must be called *after* you've set up the variables above, as those
  // variables are only written during this function and changing them later
  // won't actually propagate the settings to the device.
  SimbleeForMobile.begin();
}

void loop() 
{
  // There are two low power modes: Ultra Low Power and Off. ULP consumes about
  // 1/10 of the power that a fully on Simblee consumes; in Off mode, the
  // device is using about 1/5000 of the normal power consumption!

  // The system can be brought out of ULP mode either on a timed basis (see the
  // tutorial for more information; broadly, pass a number of milliseconds to
  // the Simblee_ULPDelay() function and the processor will awaken that many
  // milliseconds later) or by a pin transition event. In Off mode, *only* a
  // pin event can wake the processor!

  // Simblee_pinWakeCallback() executes the passed function when a pin causes
  // the device to leave either sleep mode. Options for the second parameter
  // are HIGH, LOW, or NONE, and correspond to the triggering state of the pin.
  Simblee_pinWakeCallback(button, LOW, buttonCallback);

  // Simblee_pinWake() sets up the device to awaken from sleep mode, but does
  // NOT provide a callback function. In ULP mode, execution will resume on the
  // line after the function call to Simblee_ULPDelay(); in Off mode, the
  // processor will immediately revert to sleep mode unless a callback
  // function is available.
  //Simblee_pinWake(button, LOW);

  // Simblee_systemOff() puts the device in a very low power mode, where it
  // consumes less than 1uA of current (compared to about 5000uA during normal
  // operation). In this mode, *only* a pin transition can bring the device out
  // of sleep, and you *must* provide a callback function with
  // Simblee_pinWakeCallback() for any code to be executed!
  Simblee_systemOff();

  // Simblee_ULPDelay() causes the processor to sleep for some number of
  // milliseconds. There are utility macros defined for converting from larger,
  // more convenient units: DAY(x), HOURS(x), MINUTES(x), SECONDS(x) will each
  // cause the processor to wait for x of that number of units. Pass INFINITE
  // to delay until a pin event occurs.
  //Simblee_ULPDelay(INFINITE);

  // If a pin event woke the processor, you MUST call the
  // Simblee_resetPinWake() function for that pin, or the processor will
  // immediately exit sleep mode upon reentering it.
  Simblee_resetPinWake(button);

  // We're blinking the LED here a bit longer than in the callback function, so
  // we can differentiate between which section of code is executing.
  digitalWrite(led, HIGH);
  delay(1500);
  digitalWrite(led, LOW);

  // This function must be called regularly to process UI events.
  SimbleeForMobile.process();
}

// ui() is a SimbleeForMobile specific function which handles the specification
// of the GUI on the mobile device the Simblee connects to.
void ui()
{
  // Empty, for this sketch's purposes.
}

// This function is called whenever a UI event occurs. Events are fairly easy
// to predict; for instance, touching a button produces a "PRESS_EVENT" event.
// UI elements have default event generation settings that match their expected
// behavior, so you'll only rarely have to change them.
void ui_event(event_t &event)
{
  // Empty for this sketch's purposes.
}

// This function (the name of which is completely arbitrary) is executed after
// a pinWake event pulls the processor out of low power mode. Here, we just
// blink the LED on for 500ms, just as a visual check that we have pulled out
// of low power mode.
int buttonCallback(uint32_t button)
{
  Simblee_resetPinWake(button);
  digitalWrite(led, HIGH);
  delay(500);
  digitalWrite(led, LOW);
}

There are no SimbleeForMobile UI elements defined in this sketch; note that, when in low power mode, the Simblee dictates when the host device gets updated, so the host device cannot interact with the Simblee. A Simblee in low power mode cannot be found in the app, either, although if you are connected to a Simblee when it enters ULP mode, the app will remain connected. Entering Off mode will cause the device to disappear from the app, and the connection to be lost.