power-budget-calculator

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

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

#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

Type	Voltage	Typical Capacity	Notes
CR2032	3V	220mAh	Very low current only
2x AA Alkaline	3V	2500mAh	Good for low power
3x AA Alkaline	4.5V	2500mAh	Direct to 5V systems
4x AA Alkaline	6V	2500mAh	With LDO to 5V
18650 Li-ion	3.7V	2000-3500mAh	Rechargeable, popular
LiPo 1S	3.7V	Various	Flat, light
9V Alkaline	9V	500mAh	Poor energy density

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: state assumptions, required tools and versions, implementation steps, tests/evidence by proof stage, known limitations, and recovery/security notes.