| name | low-power-design |
| description | Optimize embedded power consumption — sleep modes, peripheral shutdown, battery life estimation, and power profiling |
| allowed-tools | ["Read","Grep"] |
| effort | high |
When to activate
- Optimizing battery life for embedded devices
- Designing sleep/wake strategies
- Profiling power consumption with current meters
- Estimating battery life from power budgets
- Implementing dynamic voltage and frequency scaling
When NOT to use
- For mains-powered devices
- For high-performance computing (power is secondary)
- For battery charger circuit design
Instructions
- Power budget. Measure each component: MCU active, MCU sleep, radio TX/RX, sensors, LEDs. Create power budget spreadsheet.
- Sleep modes. Stop (CPU halt, RAM retained), Standby (most clocks off), Shutdown (only RTC + backup RAM). Wake sources: GPIO, RTC, UART.
- Duty cycling. Active for X ms, sleep for Y ms. Duty cycle = X/(X+Y). Lower duty cycle = longer battery life.
- Peripheral management. Disable unused peripherals. Clock gating. Power down sensors between reads. Radio off between transmissions.
- Software optimization. Minimize active time. Batch sensor reads. Process locally before transmitting. Use DMA for transfers.
- Battery estimation. Battery capacity (mAh) / Average current (mA) = Hours. Account for self-discharge, temperature, load profile.
- Profiling. Current meter (Nordic PPK2, Otii). Log at high sample rate. Identify unexpected wake sources and idle current.
Example
Power Budget: Environmental Sensor (CR2032, 225mAh)
Mode | Duration | Current | Energy/cycle
--------------|----------|----------|-------------
Sleep | 295s | 2.5 µA | 0.206 µAh
Wake + Sense | 50ms | 3.2 mA | 0.044 µAh
BLE TX | 5ms | 12 mA | 0.017 µAh
Total/cycle | 300s | | 0.267 µAh
Average current: 0.267 µAh / (300/3600)h = 3.2 µA
Battery life: 225 mAh / 0.0032 mA = 70,312 hours ≈ 8.0 years
