Feature: Low Power Sleep Mode

Complexity: 🟢 Low Hardware Required: 🔧 Minor (Capacitive button or switch) User Value: ⭐⭐⭐ Essential

Overview

Implement ultra-low power deep sleep mode for the ESP32-C3 SuperMini, reducing power consumption to just 43μA when idle. The system wakes instantly when a capacitive button is touched, when motion is detected, or on timer-based schedules, making it perfect for battery-powered installations.

Benefits

Dramatically extends battery life (months to years)
Reduces power consumption by 99.9%+ when idle
Multiple wake sources (GPIO, timer, touch)
Instant wake-up response
Perfect for solar/battery powered systems
Built-in RTC for scheduled wake

Power Consumption Analysis

Active Mode

WiFi active: ~100mA
WiFi off, CPU active: ~20mA
Daily consumption: ~0.5-2.4Ah

Deep Sleep Mode

Deep sleep: ~43μA (0.043mA)
Daily consumption: ~0.001Ah
Power savings: 99.96%+

Implementation Checklist

Phase 1: Basic Sleep Implementation

Create PowerSaveController class:

class PowerSaveController {
private:
    gpio_num_t wakePin;
    unsigned long lastActivity;
    unsigned long sleepTimeout;
    RTC_DATA_ATTR int bootCount = 0;
public:
    void begin(gpio_num_t pin = GPIO_NUM_0);
    void checkAndSleep();
    void forceSleep();
    void enableWakeupByPin(gpio_num_t pin, int level);
    void enableWakeupByTimer(uint64_t time_us);
    void enableWakeupByTouch(touch_pad_t pad);
    bool isWakeFromSleep();
    esp_sleep_wakeup_cause_t getWakeupReason();
    void resetActivityTimer();
};

Implement ESP32 deep sleep API
Configure wake sources

Phase 2: Wake Trigger Hardware

Phase 3: Sleep Mode Implementation

Core sleep code for ESP32-C3:

#include <esp_sleep.h>
#include <esp_pm.h>

void PowerSaveController::forceSleep() {
    // Configure wake up sources
    esp_sleep_enable_ext0_wakeup(wakePin, 0);

    // Optional: Timer wakeup (e.g., every hour)
    // esp_sleep_enable_timer_wakeup(3600 * 1000000ULL);

    // Optional: Touch wakeup
    // esp_sleep_enable_touchpad_wakeup();

    // Store data in RTC memory
    bootCount++;

    // Enter deep sleep
    Serial.println("Going to sleep...");
    Serial.flush();
    esp_deep_sleep_start();
}

bool PowerSaveController::isWakeFromSleep() {
    return esp_sleep_get_wakeup_cause() != ESP_SLEEP_WAKEUP_UNDEFINED;
}

esp_sleep_wakeup_cause_t PowerSaveController::getWakeupReason() {
    esp_sleep_wakeup_cause_t wakeup_reason = esp_sleep_get_wakeup_cause();

    switch(wakeup_reason) {
        case ESP_SLEEP_WAKEUP_EXT0:
            Serial.println("Wakeup by external signal (RTC_IO)");
            break;
        case ESP_SLEEP_WAKEUP_TIMER:
            Serial.println("Wakeup by timer");
            break;
        case ESP_SLEEP_WAKEUP_TOUCHPAD:
            Serial.println("Wakeup by touchpad");
            break;
        default:
            Serial.println("Wakeup not by deep sleep");
            break;
    }
    return wakeup_reason;
}

Phase 4: Peripheral Management

Before Sleep:

void prepareForSleep() {
    // Turn off WiFi
    WiFi.disconnect(true);
    WiFi.mode(WIFI_OFF);

    // Turn off Bluetooth
    btStop();

    // Power down RFID (via GPIO or MOSFET)
    digitalWrite(RFID_POWER_PIN, LOW);

    // Mute audio
    digitalWrite(JQ6500_POWER_PIN, LOW);

    // Turn off LEDs
    digitalWrite(8, LOW); // Blue LED

    // Flush serial buffers
    Serial.flush();
}

After Wake:

void wakeupInit() {
    // Check wake reason
    esp_sleep_wakeup_cause_t wakeup_reason = getWakeupReason();

    // Re-initialize based on wake reason
    if (wakeup_reason == ESP_SLEEP_WAKEUP_EXT0) {
        // Quick wake for card scan
        rfid.begin();
        audio.begin();
    } else if (wakeup_reason == ESP_SLEEP_WAKEUP_TIMER) {
        // Periodic wake - maybe check for OTA updates
        WiFi.begin(ssid, password);
    }
}

Phase 5: Activity-Based Sleep

Phase 6: Touch Sensor Setup

Built-in Touch Support:

void setupTouch() {
    // Initialize touch pad
    touchAttachInterrupt(T0, touchCallback, TOUCH_THRESHOLD);

    // Configure for sleep wakeup
    esp_sleep_enable_touchpad_wakeup();
}

void touchCallback() {
    // Touch detected - reset activity timer
    powerSave.resetActivityTimer();
}

Phase 7: Power Optimization

Dynamic Power Management:

// Configure power management
esp_pm_config_esp32c3_t pm_config = {
    .max_freq_mhz = 160,
    .min_freq_mhz = 10,
    .light_sleep_enable = true
};
esp_pm_configure(&pm_config);

Light Sleep for Short Delays:

// Use light sleep instead of delay()
vTaskDelay(100 / portTICK_PERIOD_MS);

Hardware Connections

Touch Sensor Wake (Built-in)

Metal Surface ---- 1MΩ resistor ---- GPIO (T0-T9)
                                      |
                                 ESP32-C3 Touch Pin

PIR Motion Sensor Wake

ESP32 GPIO -------- HC-SR501 OUT
GND --------------- HC-SR501 GND
3.3V -------------- HC-SR501 VCC

RFID Power Control

ESP32 GPIO ---- Gate (MOSFET) ---- RFID VCC
                      |
                    Source -------- 5V
                      |
                    Drain --------- RFID Power

Testing Checklist

Configuration Options

// Power save configuration
#define ENABLE_SLEEP_MODE true
#define SLEEP_TIMEOUT_MS 30000        // 30 seconds
#define WAKE_GPIO GPIO_NUM_0          // Button wake pin
#define TOUCH_THRESHOLD 40            // Touch sensitivity
#define PERIODIC_WAKE_HOURS 6         // Wake every 6 hours
#define MIN_BATTERY_VOLTAGE 3.0       // Sleep if battery low
#define USE_LIGHT_SLEEP_DELAY true    // Use light sleep in delays

Power Consumption Examples

Without Sleep Mode (24/7 operation)

50mA average × 24h = 1.2Ah/day
2000mAh battery = 1.7 days runtime

With Deep Sleep (10 uses/day, 1min each)

Active: 50mA × 10min = 8.3mAh
Sleep: 0.043mA × 1430min = 1.0mAh
Total: 9.3mAh/day
2000mAh battery = 215 days runtime

With Solar Panel (1W panel)

Solar input: ~200mAh/day (average)
Consumption: 9.3mAh/day
Indefinite runtime with surplus charging

ESP32-C3 Sleep Modes

Mode	Current	Wake Time	Use Case
Active	20-100mA	-	Normal operation
Modem Sleep	15mA	<1ms	WiFi periodic
Light Sleep	0.8mA	<1ms	Short pauses
Deep Sleep	43μA	3ms	Long idle periods

Troubleshooting

Won’t Wake: Check GPIO pullup/pulldown
High Sleep Current: Ensure WiFi/BT off
Touch Too Sensitive: Adjust threshold
Slow Wake: Minimize reinit code

Future Enhancements

ULP coprocessor for ultra-low power sensing
Solar MPPT charging integration
LoRa wake-on-radio
Accelerometer wake on vibration
Scheduled wake with RTC
Power harvesting from door movement