power-budget-calculator

What this skill does

# Power Budget Calculator

Estimates power consumption and battery life for embedded projects.

## Resources

- **scripts/calculate_power.py** - Python calculator with component database, duty cycle support, battery life estimation
- **references/component-database.md** - Comprehensive current draw reference from datasheets  
- **assets/example-project.json** - Sample project configuration

## Quick Start

Run the calculator interactively:
```bash
uv run --no-project scripts/calculate_power.py --interactive
```

Or calculate for a single component:
```bash
uv run --no-project scripts/calculate_power.py --component ESP32 --mode deep_sleep --duty 95
```

Load a project configuration:
```bash
uv run --no-project scripts/calculate_power.py --json assets/example-project.json --output report.md
```

List all components in database:
```bash
uv run --no-project scripts/calculate_power.py --list
```

## When to Use
- "How long will my battery last?"
- "What size battery do I need?"
- "How much current does my project draw?"
- Planning battery-powered projects
- Optimizing for low power

## Workflow

### Step 1: Gather Component List

Ask user for:
1. Microcontroller (model and operating mode)
2. All sensors and modules
3. Displays
4. Actuators (motors, LEDs, relays)
5. Communication (WiFi, Bluetooth, LoRa)
6. Operating profile (always on vs. duty cycle)

### Step 2: Calculate Power Budget

Run `scripts/calculate_power.py --interactive` for guided calculation, or use this template:

```markdown
# Power Budget: [Project Name]

## Operating Conditions
- Supply Voltage: [V]
- Operating Modes: [Active/Sleep cycles]
- Duty Cycle: [X% active, Y% sleep]

## Component Current Draw

### Always-On Components
| Component | Voltage | Current | Power | Notes |
|-----------|---------|---------|-------|-------|
| [name] | [V] | [mA] | [mW] | [conditions] |
| ... | ... | ... | ... | ... |
| **Subtotal** | - | **[mA]** | **[mW]** | - |

### Active Mode Only
| Component | Voltage | Current | Power | Duty % |
|-----------|---------|---------|-------|--------|
| [name] | [V] | [mA] | [mW] | [%] |
| ... | ... | ... | ... | ... |
| **Subtotal** | - | **[mA]** | **[mW]** | - |

### Peak Current Events
| Event | Current | Duration | Frequency |
|-------|---------|----------|-----------|
| [WiFi TX] | [mA] | [ms] | [per hour] |
| ... | ... | ... | ... |

## Power Calculations

### Average Current
```
I_avg = (I_active × t_active + I_sleep × t_sleep) / t_total
I_avg = ([X]mA × [Y]s + [Z]mA × [W]s) / [T]s
I_avg = [result] mA
```

### Battery Life Estimate
```
Capacity: [X] mAh
Efficiency factor: 0.8 (80% usable)
Effective capacity: [X × 0.8] mAh

Runtime = Effective capacity / I_avg
Runtime = [X] mAh / [Y] mA
Runtime = [Z] hours ([days] days)
```

## Recommendations
- [Power optimization suggestions]
- [Battery type recommendation]
- [Sleep mode configuration]
```

## Current Draw Database

### Microcontrollers

#### Arduino (ATmega328P @ 5V)
| Mode | Current | Notes |
|------|---------|-------|
| Active (16MHz) | 15-20mA | No peripherals |
| Idle | 6mA | CPU stopped, peripherals on |
| Power-down | 0.1µA | Only WDT/external interrupt |
| With USB-Serial | +50mA | CH340/FTDI chip always on |

#### ESP32 (WROOM-32)
| Mode | Current | Notes |
|------|---------|-------|
| Active (WiFi TX) | 160-260mA | Peak during transmission |
| Active (WiFi RX) | 95-100mA | Listening |
| Active (no WiFi) | 20-68mA | CPU only |
| Modem-sleep | 20mA | WiFi off, CPU on |
| Light-sleep | 0.8mA | CPU paused |
| Deep-sleep | 10µA | RTC only |
| Hibernation | 5µA | RTC off |

#### ESP32-C3
| Mode | Current | Notes |
|------|---------|-------|
| Active (WiFi TX) | 320mA peak | Brief spikes |
| Active (BLE) | 50-100mA | During advertising |
| Active (no radio) | 25-35mA | CPU at 160MHz |
| Light-sleep | 130µA | Auto wake |
| Deep-sleep | 5µA | RTC on |

#### RP2040 (Pico)
| Mode | Current | Notes |
|------|---------|-------|
| Active (both cores) | 25-50mA | Depends on clock |
| Single core | 15-25mA | One core dormant |
| Dormant | 0.18mA | Wake on GPIO/RTC |
| Sleep | 1.3mA | |

#### RP2040 (Pico W)
| Mode | Current | Notes |
|------|---------|-------|
| WiFi active | 50-150mA | During TX |
| WiFi idle | 30-40mA | Connected, listening |
| WiFi off | 25-50mA | Radio disabled |

### Sensors

| Sensor | Active | Sleep | Notes |
|--------|--------|-------|-------|
| DHT22 | 1.5mA | 50µA | During read |
| BME280 | 0.35mA | 0.1µA | Forced mode |
| BMP280 | 0.27mA | 0.1µA | |
| MPU6050 | 3.8mA | 5µA | All axes |
| DS18B20 | 1.5mA | 1µA | During conversion |
| HC-SR04 | 15mA | 2mA | No true sleep |
| VL53L0X | 19mA | 5µA | During ranging |
| MAX30102 | 600µA | 0.7µA | Low power mode |
| BH1750 | 120µA | 1µA | Power down mode |
| GPS (NEO-6M) | 45mA | 11mA | Backup mode |

### Displays

| Display | Active | Off/Sleep | Notes |
|---------|--------|-----------|-------|
| 16x2 LCD (backlight) | 80-120mA | 1mA | Backlight dominates |
| 16x2 LCD (no backlight) | 1-2mA | 1mA | |
| SSD1306 OLED 128x64 | 8-20mA | 10µA | Depends on content |
| SSD1306 OLED 128x32 | 5-15mA | 10µA | |
| ST7735 TFT | 20-40mA | 20mA | Backlight always on |
| ILI9341 TFT | 50-80mA | 50mA | |
| E-Paper 2.9" | 8mA | 0µA | Only during refresh |

### Communication Modules

| Module | TX Peak | RX/Idle | Sleep | Notes |
|--------|---------|---------|-------|-------|
| ESP8266 (module) | 170mA | 70mA | 20µA | Deep sleep |
| NRF24L01 | 11.3mA | 13.5mA | 0.9µA | |
| HC-05 Bluetooth | 40mA | 8mA | 2mA | |
| RFM95 LoRa | 120mA | 10mA | 0.2µA | |
| SIM800L GSM | 2A peak | 15mA | 1mA | Needs big cap! |

### Actuators

| Component | Current | Notes |
|-----------|---------|-------|
| LED (typical) | 10-20mA | Through resistor |
| RGB LED (each color) | 20mA | Per channel |
| WS2812B NeoPixel | 60mA max | Full white |
| SG90 Servo (idle) | 10mA | No load |
| SG90 Servo (moving) | 200-500mA | Under load |
| MG996R Servo | 500-900mA | Under load |
| Small DC motor | 100-500mA | Varies with load |
| 5V Relay module | 70-100mA | Coil energized |
| Buzzer (passive) | 30mA | |

## Sleep Mode Configurations

### ESP32 Deep Sleep Template
```cpp
#include <esp_sleep.h>

#define uS_TO_S_FACTOR 1000000ULL
#define TIME_TO_SLEEP 60  // seconds

void setup() {
    // Do measurements here
    
    // Configure wake-up source
    esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);
    
    // Enter deep sleep
    esp_deep_sleep_start();
}

void loop() {
    // Never reached
}
```

### Arduino Power-Down Template
```cpp
#include <avr/sleep.h>
#include <avr/wdt.h>

void enterSleep() {
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);
    sleep_enable();
    sleep_mode();  // Sleep here
    sleep_disable();
}

// Wake on watchdog or external interrupt
ISR(WDT_vect) {
    // Wake up
}
```

## Power Optimization Checklist

### Hardware
- [ ] Remove power LED (saves 5-10mA)
- [ ] Remove USB-Serial chip for battery operation
- [ ] Use LDO with low quiescent current (<10µA)
- [ ] Add MOSFET to power-gate high-current peripherals
- [ ] Use pull-downs on unused pins
- [ ] Disable ADC when not reading

### Software
- [ ] Use sleep modes between readings
- [ ] Reduce clock speed if possible
- [ ] Batch data and transmit less frequently
- [ ] Turn off WiFi/BLE when not needed
- [ ] Disable brown-out detector in deep sleep
- [ ] Use interrupts instead of polling

### Design Patterns

**Power Gating:**
```
       VCC
        │
    [P-MOSFET] ← GPIO (LOW = ON)
        │
    [Sensor/Module]
        │
       GND
```

**Duty Cycling Formula:**
```
I_average = (I_active × T_active + I_sleep × T_sleep) / T_total

Example: Sensor reads every 5 minutes
- Active: 50mA for 2 seconds
- Sleep: 10µA for 298 seconds

I_avg = (50mA × 2s + 0.01mA × 298s) / 300s
I_avg = (100 + 2.98) / 300
I_avg = 0.34mA

With 2000mAh battery:
Runtime = 2000mAh × 0.8 / 0.34mA = 4706 hours = 196 days
```

## Battery Reference

### Common Battery Types

| Type | Voltage | Typical Capacity | Notes |
|------|---------|--------