Electronics Guide

Texas Instruments MSP430 LaunchPad

The MSP430 LaunchPad series represents one of the most established ultra-low-power development ecosystems. Texas Instruments designed the MSP430 microcontroller family from the ground up for low-power operation, achieving standby currents in the sub-microamp range.

• MSP430FR Series: Features FRAM (ferroelectric RAM) non-volatile memory with virtually unlimited write endurance and write speeds 100 times faster than flash, enabling efficient data logging with minimal energy
• Active mode current: As low as 100 microamps per MHz at 3V, among the lowest in the industry
• Standby modes: Multiple low-power modes ranging from 0.4 microamps in standby with RAM retention to 20 nanoamps in complete shutdown
• Wake-up time: Less than 5 microseconds from standby to active execution, minimizing energy wasted during transitions
• Integrated peripherals: Low-power analog comparators, ADCs with internal reference, and configurable timers that operate during sleep

The MSP430 LaunchPad includes an integrated eZ-FET debugger that supports EnergyTrace technology, allowing real-time power measurement with nanosecond resolution during firmware development.

Silicon Labs EFM32 Giant Gecko and Pearl Gecko

Silicon Labs EFM32 microcontrollers employ an ARM Cortex-M architecture optimized for energy efficiency. The development kits provide comprehensive tools for ultra-low-power design:

• Energy Modes: Five distinct energy modes (EM0-EM4) with progressively lower power consumption, down to 20 nanoamps in EM4
• Peripheral Reflex System (PRS): Hardware-based peripheral interconnection allowing sensor processing without CPU intervention
• Low Energy Sensor Interface (LESENSE): Autonomous peripheral for capacitive sensing and environmental monitoring during sleep
• Advanced Energy Monitoring: On-board current measurement circuitry with direct correlation to source code execution
• Simplicity Studio: Integrated development environment with energy profiler and power estimation tools

The Giant Gecko and Pearl Gecko starter kits include expansion headers compatible with various sensor and communication add-on boards, facilitating rapid prototyping of complete low-power systems.

Nordic Semiconductor nRF52 Development Kits

Nordic Semiconductor's nRF52 series combines Bluetooth Low Energy (BLE) wireless connectivity with ultra-low-power ARM Cortex-M4 processing. These platforms are particularly suited for wireless sensor and wearable applications:

• Integrated radio: 2.4 GHz multi-protocol radio supporting Bluetooth LE, Thread, Zigbee, and proprietary protocols
• Radio current consumption: 5.5 mA at 0 dBm transmit power, among the lowest for integrated wireless solutions
• System-on-chip design: Reduces component count and associated power losses from multiple ICs
• Power Profiler Kit: Dedicated hardware for measuring current consumption down to 200 nanoamps with 100 nanosecond sampling
• SoftDevice: Pre-certified Bluetooth stack with optimized power management and connection parameter control

The nRF52840 DK includes USB connectivity, NFC tag capability, and extensive GPIO for interfacing with sensors and actuators in wireless applications.

STMicroelectronics STM32L Series

The STM32L family provides ultra-low-power operation within the extensive STM32 ecosystem. STMicroelectronics offers several development boards optimized for power-sensitive applications:

• STM32L4 and STM32L5 Nucleo boards: Mainstream low-power platforms with rich peripheral sets and security features
• STM32L0 Discovery: Entry-level ultra-low-power platform achieving sub-microamp standby current
• Batch Acquisition Mode (BAM): DMA-based data collection allowing the CPU to remain in sleep during sensor sampling
• Low-power timer (LPTIM): Continues counting during stop modes, enabling timed wake-up with minimal power
• STM32CubeMonitor-Power: Software tool for real-time current monitoring and analysis on supported boards

Solar Energy Harvesting

Solar or photovoltaic energy harvesting captures light energy and converts it to electricity. Development kits in this category typically include:

• Solar cell modules: Various sizes and technologies including monocrystalline, polycrystalline, and amorphous silicon cells optimized for indoor or outdoor light
• Maximum Power Point Tracking (MPPT): Circuits that continuously adjust the operating point to extract maximum power as light conditions change
• Energy storage management: Battery or supercapacitor charging with overcharge and deep discharge protection
• Cold-start capability: Circuits that can begin operation from a completely discharged state using only harvested energy
• Indoor light optimization: Components tuned for the spectrum of artificial lighting, which differs significantly from sunlight

The Texas Instruments BQ25570 evaluation module exemplifies solar harvesting design, featuring a boost charger with integrated MPPT and an extremely low quiescent current of 488 nanoamps. The module can extract power from sources as low as 100 millivolts.

Thermal Energy Harvesting

Thermoelectric generators (TEGs) convert temperature differentials directly into electrical energy using the Seebeck effect. Thermal harvesting kits address applications where consistent temperature gradients exist:

• Peltier modules: Bismuth telluride thermoelectric elements optimized for energy generation from small temperature differences
• Low-voltage boost converters: DC-DC converters capable of stepping up the tens of millivolts produced by TEGs to usable voltage levels
• Heat sink design: Thermal management components that maintain the temperature differential across the TEG
• Body heat harvesting: Configurations optimized for the typical 10-15 degree Celsius difference between skin and ambient air
• Industrial waste heat: Higher-power configurations for capturing energy from pipes, motors, and process equipment

The Analog Devices LTC3108 evaluation kit demonstrates thermal harvesting with a boost converter that operates from input voltages as low as 20 millivolts, enabling operation from single thermoelectric elements with temperature differences of only a few degrees.

Vibration and Kinetic Energy Harvesting

Piezoelectric and electromagnetic transducers capture mechanical energy from vibration, motion, or pressure and convert it to electricity:

• Piezoelectric elements: Ceramic or polymer materials that generate voltage when mechanically stressed, suitable for vibration frequencies from 10 Hz to several kHz
• Electromagnetic harvesters: Moving magnet or coil assemblies that generate current from linear or rotational motion
• Resonant frequency tuning: Mechanical structures designed to match the dominant vibration frequency of the target environment
• Rectification circuits: Full-bridge rectifiers and voltage doublers optimized for the AC output of mechanical harvesters
• Shock and impact harvesting: Configurations designed to capture energy from discrete mechanical events rather than continuous vibration

The Mide Volture vibration harvesting evaluation kit includes piezoelectric cantilever elements, rectification circuitry, and storage capacitors, providing a complete platform for characterizing vibration sources and optimizing harvester placement.

RF Energy Harvesting

Radio frequency energy harvesting captures electromagnetic energy from ambient wireless signals or dedicated RF power transmitters:

• Antenna design: Tuned antennas optimized for specific frequency bands (WiFi, cellular, broadcast) or wideband capture
• Rectenna circuits: Combined antenna and rectifier systems that convert RF energy directly to DC power
• Impedance matching: Networks that maximize power transfer from antenna to rectifier across varying signal strengths
• Multi-band harvesting: Systems that combine energy from multiple frequency bands to increase total harvested power
• Wireless power transfer: Near-field systems using dedicated transmitters for higher power levels at closer range

The Powercast P21XXCSR-EVB evaluation board demonstrates RF harvesting using the 915 MHz ISM band, achieving several milliwatts of harvested power at ranges up to 25 meters from a dedicated transmitter.

Multi-Source Energy Harvesting

Advanced energy harvesting systems combine multiple ambient energy sources to improve reliability and total energy availability:

• Hybrid power management: ICs that can accept inputs from solar, thermal, and piezoelectric sources simultaneously
• Source prioritization: Intelligent switching between energy sources based on availability and efficiency
• Common storage architecture: Single battery or supercapacitor charged from multiple harvester types
• Complementary harvesting: Combining sources that are active at different times (solar during day, thermal from equipment operation)

The e-peas AEM10941 evaluation kit exemplifies multi-source harvesting, accepting inputs from photovoltaic, thermoelectric, or piezoelectric sources through a single power management IC with 94% conversion efficiency.

Dedicated Power Profilers

Purpose-built power profiling instruments provide the dynamic range and sampling rate needed to characterize low-power systems:

• Qoitech Otii Arc: Combined power supply and measurement unit with 1 nanoamp to 5 amp range, 200 kHz sampling, and software correlation to firmware execution
• Nordic Power Profiler Kit II: Measures from 200 nanoamps to 70 milliamps with nanosecond time resolution, designed for battery-operated wireless devices
• Joulescope: Open-source power analyzer supporting 10-amp continuous measurement with 2 MHz bandwidth and current-time integration
• Monsoon Power Monitor: Industry-standard mobile device power analyzer capable of measuring submicrosecond current transients
• Keysight N6705C: Precision DC power analyzer with seamless auto-ranging from nanoamps to amps for comprehensive device characterization

These tools typically provide software interfaces that correlate power measurements with source code execution, enabling identification of power-hungry functions and optimization opportunities.

On-Board Power Measurement

Many low-power development boards include integrated power measurement circuitry:

• TI EnergyTrace: Built into MSP430 LaunchPads, provides real-time power measurement with correlation to code execution and energy state logging
• Silicon Labs AEM: Advanced Energy Monitor on EFM32 starter kits measures current down to 100 nanoamps with timestamps synchronized to debugger events
• STM32 PowerShield: Add-on board for Nucleo platforms enabling accurate current measurement across seven decades of dynamic range
• Current sense amplifiers: INA219 and INA226 based circuits integrated on development boards for basic current monitoring via I2C

On-board measurement eliminates the need for external equipment during initial development, though dedicated profilers typically offer superior accuracy and resolution for final optimization.

Energy Measurement Techniques

Accurate low-power measurement requires careful attention to measurement methodology:

• Shunt resistor selection: Balancing measurement resolution against voltage drop and burden; typical values range from 1 ohm to 100 ohms depending on current range
• Settling time: Allowing sufficient time for current to stabilize after mode transitions before recording measurements
• Average vs. peak current: Understanding that battery life depends on average current while peak current affects voltage regulator selection
• Temperature effects: Accounting for leakage current increases at elevated temperatures that may not appear in lab testing
• Real vs. simulated loads: Testing with actual sensors and peripherals rather than assuming datasheet typical values

Battery Life Estimation

Converting power measurements to battery life predictions requires accounting for real-world factors:

• Duty cycle analysis: Calculating weighted average current based on time spent in each operating mode
• Battery capacity derating: Accounting for temperature, discharge rate, and aging effects on usable capacity
• Self-discharge: Including battery self-discharge rate, particularly important for multi-year deployments
• Cutoff voltage: Determining the minimum voltage at which the system remains functional to establish usable capacity
• Margin factors: Applying appropriate safety factors for manufacturing variation and environmental conditions

Software tools such as the TI Battery Life Estimator and Silicon Labs Energy Profiler automate these calculations based on measured power profiles and battery specifications.

Non-Intrusive Debugging

Maintaining debug capability without affecting power consumption requires careful consideration:

• Debug power isolation: Physically disconnecting debug interface power to allow true sleep current measurement
• Wake-on-debug: Configuring debug interfaces to wake the processor only when actively debugging
• Trace buffers: Using on-chip trace storage to capture execution history without maintaining debug connection
• GPIO instrumentation: Toggling output pins to indicate state transitions, measurable with logic analyzer or oscilloscope
• UART logging: Low-power serial output for status messages, disabled in production firmware

Sleep Mode Verification

Verifying correct entry and exit from low-power modes is critical for achieving target battery life:

• Current signature analysis: Confirming that measured sleep current matches expected values for the configured mode
• Wake source identification: Verifying that only intended wake sources are active and spurious wakes are eliminated
• Peripheral state verification: Ensuring all peripherals are correctly powered down or placed in low-power states
• Clock configuration: Confirming that high-frequency clocks are disabled during sleep and wake-up clock switching functions correctly
• Leakage current sources: Identifying GPIO pins, unused peripherals, or external components contributing to sleep current

Common Sleep Mode Issues

Several common problems prevent achieving minimum sleep current:

• Floating inputs: Unconnected GPIO pins configured as inputs can oscillate, consuming significant current; solution is to enable pull-up or pull-down resistors or configure as outputs
• Uncleared interrupt flags: Pending interrupts may prevent entry to deepest sleep modes or cause immediate wake-up
• Active debug session: Debug connections may override sleep mode entry or enable clocks that should be disabled
• Peripheral clock leakage: Some peripherals must have clocks explicitly disabled even when the peripheral itself is not in use
• External component current: Sensors, voltage dividers, and indicator LEDs may draw current that exceeds MCU sleep current
• Regulator quiescent current: LDO or switching regulator overhead current that persists regardless of load

Power State Machines

Complex low-power systems often implement formal power state machines to manage transitions:

• State definitions: Clearly defined operating modes with specified active peripherals and current budgets
• Transition triggers: Events that cause movement between power states (timers, interrupts, communication)
• Entry and exit sequences: Documented procedures for configuring hardware when entering or leaving each state
• State persistence: Maintaining state information across sleep cycles using retained RAM or non-volatile storage
• Recovery procedures: Handling unexpected resets or power interruptions gracefully

Compiler and Code Optimization

Software efficiency directly impacts power consumption through reduced active time:

• Optimization levels: Compiler optimization for speed (-O2, -O3) reduces time spent in active mode
• Loop unrolling: Trades code size for reduced loop overhead in timing-critical sections
• Inline functions: Eliminates function call overhead for frequently called routines
• Data alignment: Proper alignment reduces memory access cycles on architectures with alignment restrictions
• DMA utilization: Offloading data transfers to DMA allows CPU to sleep during bulk operations

Power-Aware Operating Systems

Real-time operating systems designed for low-power applications provide automatic power management:

• FreeRTOS tickless idle: Stops the system tick timer during idle periods to eliminate periodic wake-ups
• Zephyr power management: Integrated power state management with automatic selection of appropriate sleep modes
• Mbed OS deep sleep: Automatic entry to deep sleep when all threads are idle with preservation of timing accuracy
• RIOT OS: Open-source OS specifically designed for IoT devices with minimal overhead and power awareness
• Contiki-NG: Event-driven OS for constrained devices with duty-cycling radio protocols

Communication Protocol Optimization

Wireless communication often dominates power budgets; protocol optimization is essential:

• Connection intervals: Increasing Bluetooth LE connection interval from 7.5 ms to seconds dramatically reduces radio duty cycle
• Batched transmissions: Accumulating data and sending in bursts rather than individual packets reduces radio startup overhead
• Adaptive data rates: Adjusting transmission power and data rate based on link quality to minimize time on air
• Compression: Reducing payload size to shorten transmission duration
• Wake-on-radio: Protocols that allow the receiver to sleep until a preamble is detected

Sensor Duty Cycling

Intelligent sensor management reduces the energy required for data acquisition:

• Sample rate optimization: Matching sample rate to actual information bandwidth requirements
• Sensor power gating: Completely removing power from sensors between measurements
• Wake-up sensors: Using ultra-low-power sensors to trigger the main system only when events occur
• Local processing: Performing threshold detection or signal processing locally rather than transmitting raw data
• Adaptive sampling: Increasing sample rate only when activity is detected

Indoor Solar-Powered Sensor Nodes

Indoor light harvesting presents unique challenges due to lower illumination levels and different spectral content compared to sunlight:

• Amorphous silicon cells: Better performance under indoor fluorescent and LED lighting compared to crystalline cells
• Harvested power levels: Typically 10-100 microwatts per square centimeter under office lighting (500 lux)
• Energy storage: Supercapacitors or rechargeable lithium batteries to bridge periods of darkness
• Power management: Ultra-low quiescent current regulators that do not consume more than the harvested energy
• Reference designs: Texas Instruments TIDA-00242 demonstrates perpetual operation of a temperature sensor under indoor lighting

Body Heat Powered Wearables

Thermoelectric harvesting from body heat enables battery-free wearable devices:

• Temperature differential: Typical 10-15 degrees Celsius between skin and ambient air provides usable gradient
• TEG output: Single-element TEGs produce 20-50 millivolts open circuit at body temperature differentials
• Boost converter requirements: Startup from tens of millivolts with sub-microamp quiescent current
• Achievable power: 10-100 microwatts typical for wristband form factors
• Application examples: Heart rate monitors, activity trackers, and continuous health monitoring devices

Vibration-Powered Industrial Sensors

Industrial machinery provides consistent vibration sources for piezoelectric energy harvesting:

• Vibration characterization: Identifying dominant frequencies using accelerometers or vibration analyzers
• Resonant harvester design: Tuning mechanical resonance to match dominant vibration frequency for maximum power extraction
• Power levels: Milliwatts achievable from industrial motors and rotating equipment
• Application examples: Wireless vibration monitors, temperature sensors on motors, and valve position sensors
• Retrofit installations: Adding intelligence to existing equipment without running power cables

RF-Powered RFID Sensors

Combining RFID technology with sensors enables battery-free data collection:

• Passive RFID principle: Harvesting energy from the reader's RF field to power sensor measurement and data transmission
• Read range: Typically 1-10 meters depending on reader power and antenna design
• Sensor integration: Temperature, humidity, and strain sensors integrated into RFID tag ICs
• Data logging: Some tags include memory for storing measurements between reads
• Application examples: Cold chain monitoring, structural health monitoring, and equipment tracking with condition sensing

Power Budget Analysis

Begin platform selection by establishing the available power budget:

• Battery-powered: Calculate required operating life and divide battery capacity by this duration to establish average current budget
• Energy harvesting: Characterize expected harvested power under worst-case conditions (minimum light, temperature differential, or vibration)
• Hybrid systems: Determine primary power source and size battery backup for periods without harvested energy
• Margin allocation: Reserve 20-30% margin for manufacturing variation and environmental uncertainty

Functionality Requirements

Match platform capabilities to application requirements:

• Processing power: Simple threshold monitoring needs minimal computation; signal processing or machine learning requires more capable processors
• Wireless connectivity: BLE, Zigbee, LoRa, or proprietary protocols each have different power profiles and range characteristics
• Sensor interfaces: Required ADC resolution, I2C/SPI peripherals, and analog front-end capabilities
• Memory requirements: Data logging needs, firmware complexity, and over-the-air update capability
• Security: Cryptographic acceleration and secure boot for sensitive applications

Development Ecosystem

Consider the available tools and support infrastructure:

• IDE and toolchain: Quality of development environment, debugging capabilities, and learning curve
• Power analysis tools: Availability of integrated power measurement and profiling
• Reference designs: Existing designs that can accelerate development
• Community support: Forums, examples, and third-party resources
• Certification support: Pre-certified modules and regulatory compliance assistance

Hardware Design Considerations

• Voltage rail optimization: Running at lower supply voltage reduces both active and leakage current
• Component selection: Choose low-power variants of sensors, regulators, and passive components
• Power domain partitioning: Separate power domains allow selective shutdown of unused sections
• Decoupling strategy: Proper decoupling prevents current spikes from affecting sensitive analog circuits
• Test point provision: Include current measurement points at critical locations for debugging

Firmware Development Practices

• Power-aware design: Consider power implications of every function from initial architecture
• Peripheral initialization: Disable unused peripherals and clocks immediately at startup
• Interrupt-driven operation: Avoid polling; use interrupts to wake from sleep when events occur
• Time budgeting: Allocate specific time budgets for each operation and verify compliance
• Regression testing: Include power consumption in automated testing to catch regressions

Validation and Testing

• Comprehensive profiling: Measure power in all operating modes and transitions
• Environmental testing: Verify power consumption across temperature range
• Long-term testing: Run extended tests to identify any drift or unexpected wake events
• Production testing: Establish pass/fail criteria for manufacturing power verification
• Field monitoring: Include battery voltage logging or reporting for deployed units