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:

uv run --no-project scripts/calculate_power.py --interactive

Or calculate for a single component:

uv run --no-project scripts/calculate_power.py --component ESP32 --mode deep_sleep --duty 95

Load a project configuration:

uv run --no-project scripts/calculate_power.py --json assets/example-project.json --output report.md

List all components in database:

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:

# 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

Iavg = (Iactive × tactive + Isleep × tsleep) / ttotal Iavg = ([X]mA × [Y]s + [Z]mA × [W]s) / [T]s Iavg = [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)

ESP32 (WROOM-32)

ESP32-C3

RP2040 (Pico)

RP2040 (Pico W)

Sensors

Displays

Communication Modules

Actuators

Sleep Mode Configurations

ESP32 Deep Sleep Template

#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

#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

Voltage Over Discharge

18650/LiPo Discharge Curve:

Capacity%   Voltage
─────────────────────
100%        4.2V
80%         3.9V
50%         3.7V
20%         3.5V
0%          3.0V (cut-off!)

Never discharge below 3.0V - damages cell!

Alkaline AA Discharge:

Capacity%   Voltage (per cell)
─────────────────────────────
100%        1.5V
50%         1.2V
0%          0.9V

Many devices stop working below 1.1V/cell

Quick Calculator

Enter your values:

Always-on current: ______ mA
Active current: ______ mA
Active time: ______ seconds
Sleep current: ______ mA  
Sleep time: ______ seconds
Battery capacity: ______ mAh

Average current = (Active_mA × Active_s + Sleep_mA × Sleep_s) / Total_s
                = (_____ × _____ + _____ × _____) / _____
                = _____ mA

Runtime = Capacity × 0.8 / Average_current
        = _____ × 0.8 / _____
        = _____ hours
        = _____ days

Shared Output Contract

Use [the shared Arduino skill contract](../../docs/arduino-skill-contract.md): state assumptions, required tools and versions, implementation steps, tests/evidence by proof stage, known limitations, and recovery/security notes.