Ultra-Low Power with MSP430

If the LaunchPad programmer doesn't feature EnergyTrace, the programmer of another LaunchPad can be used.

In this example, the MSP430G2 LaunchPad doesn't not feature EnergyTrace, so we are going to use the EnergyTrace-compatible programmer from the LaunchPad MSP430FR5969.

Here's the schematic of the EnergyTrace implementation.

The EnergyTrace-compatible programmer from the LaunchPad MSP430FR5969 is connected to the LaunchPad MSP430G2553. Remove all the jumpers and connect the +3.3V and Ground lines.

delay() vs. sleep()

The loop() blinks the LED twice, enters delay() state for 10 seconds, then blinks once, and goes to sleep() for 10 seconds.

With sleep() and sleepSeconds(), the MCU enters LPM3.

CPU is disabled.
MCLK and SMCLK are disabled.
DCO's dc generator is disabled.
ACLK remains active.

As a consequence of SMCLK being disabled, background processes such as Serial transmit and receive will halt or get scrambled.

sleep() applies for milliseconds and sleepSeconds() for seconds.

Notice the difference of power consumption between delay() and sleep().

delay() requires 3 mW or 1 mA
sleep() requires less than 0.1 mW.

The peaks correspond to the LED blinking twice before delay(), and once before sleep().

EnergyTrace also estimates the battery life, here close to half a year with 2 AA batteries.

suspend() and wakeup()

With suspend(), the MCU enters LPM4.

CPU is disabled.
ACLK is disabled.
MCLK and SMCLK are disabled.
DCO's dc generator is disabled.
Crystal oscillator is stopped.

The MCU can only react to a hardware interrupt, triggered here by PUSH2. The interrupt calls the buttonISR() routine and launches wakeup() to return to active mode.

This example is based on Frank Milburn's code (June 2015), which is derived from @spirilis at 43oh.com

The peak corresponds to the LED turned on and happens just after PUSH2 is pressed.

Conclusion

Using sleep() instead of delay() and implementing a hardware interrupt save energy and increase battery life.

EnergyTrace provides a convenient way for measuring and comparing power consumptions.