Power Management

Power Supply Options

The Wireless Tracker supports multiple power sources with automatic switching.

Input Specifications

Power Mode	Min	Typical	Max	Unit
Type-C USB (≥500mA)	4.7	5.0	6.0	V
Lithium battery (≥250mA)	3.3	3.7	4.2	V
5V pin (≥500mA)	4.7	5.0	6.0	V
3V3 pin (≥150mA)	2.7	3.3	3.5	V

Output Specifications

Output	Max Current	Notes
3.3V Pin	500 mA	Regulated output
5V Pin	500 mA	USB powered only
Vext Pin	350 mA	Powers TFT + GNSS

Power Consumption

By Operating Mode

Mode	USB Power	Battery Power
Wi-Fi Scanning	100 mA	74 mA
Wi-Fi Access Point	150 mA	111 mA
Bluetooth Active	102 mA	75 mA
GNSS Active	120 mA	89 mA
LoRa TX @ 14 dBm	200 mA	148 mA
LoRa TX @ 17 dBm	220 mA	163 mA
LoRa TX @ 22 dBm	240 mA	178 mA
LoRa RX Only	80 mA	59 mA
Deep Sleep	2 mA	15 µA

Battery Management

The Wireless Tracker includes an integrated battery management system:

Charging: Automatic when USB connected with battery attached
Protection: Overcharge, over-discharge, short circuit
Switching: Automatic USB/battery source selection
Monitoring: Battery voltage readable via GPIO1 ADC

Reading Battery Voltage

#define VBAT_ADC_PIN   1
#define VBAT_CTRL_PIN  2

float getBatteryVoltage() {
    // Enable ADC voltage divider
    pinMode(VBAT_CTRL_PIN, OUTPUT);
    digitalWrite(VBAT_CTRL_PIN, LOW);

    // Read ADC
    int rawADC = analogRead(VBAT_ADC_PIN);

    // Disable voltage divider to save power
    digitalWrite(VBAT_CTRL_PIN, HIGH);

    // Convert to voltage
    // Formula: VBAT = ADC_Reading × (3.3V / 4095) × 4.9
    float voltage = (rawADC / 4095.0) * 3.3 * 4.9;

    return voltage;
}

int getBatteryPercent() {
    float voltage = getBatteryVoltage();

    // Simple linear approximation
    // 4.2V = 100%, 3.3V = 0%
    int percent = (int)((voltage - 3.3) / (4.2 - 3.3) * 100);

    return constrain(percent, 0, 100);
}

Battery Voltage Thresholds

Voltage	State	Approximate %
4.20 V	Full	100%
4.00 V	High	80%
3.80 V	Medium	50%
3.60 V	Low	20%
3.40 V	Critical	5%
3.30 V	Cutoff	0%

Low Power Modes

Deep Sleep

The ESP32-S3 supports ultra-low-power deep sleep mode:

#include "esp_sleep.h"

void enterDeepSleep(uint64_t sleepTimeUs) {
    // Disable peripherals
    digitalWrite(GNSS_PWR_PIN, LOW);  // V1.1
    digitalWrite(TFT_LED_PIN, LOW);

    // Configure wakeup
    esp_sleep_enable_timer_wakeup(sleepTimeUs);

    // Optional: wakeup on button press
    esp_sleep_enable_ext0_wakeup(GPIO_NUM_0, LOW);

    // Enter deep sleep
    esp_deep_sleep_start();
}

void setup() {
    // Check wakeup reason
    esp_sleep_wakeup_cause_t reason = esp_sleep_get_wakeup_cause();

    switch (reason) {
        case ESP_SLEEP_WAKEUP_TIMER:
            Serial.println("Woke from timer");
            break;
        case ESP_SLEEP_WAKEUP_EXT0:
            Serial.println("Woke from button");
            break;
        default:
            Serial.println("Normal boot");
            break;
    }
}

Light Sleep

For faster wake with moderate power savings:

void enterLightSleep(uint64_t sleepTimeUs) {
    esp_sleep_enable_timer_wakeup(sleepTimeUs);
    esp_light_sleep_start();
    // Execution continues here after wakeup
}

Peripheral Power Control

Vext Control (V1.1)

GPIO3 controls the Vext rail that powers the TFT display and GNSS module:

#define VEXT_PIN 3

void enableVext() {
    pinMode(VEXT_PIN, OUTPUT);
    digitalWrite(VEXT_PIN, HIGH);
}

void disableVext() {
    digitalWrite(VEXT_PIN, LOW);
}

Display Backlight

#define TFT_LED 21

void setBacklight(bool on) {
    digitalWrite(TFT_LED, on ? HIGH : LOW);
}

// PWM dimming (optional)
void setBacklightBrightness(uint8_t level) {
    analogWrite(TFT_LED, level);  // 0-255
}

Power Optimization Tips

Disable unused peripherals: Turn off Wi-Fi, Bluetooth, GNSS when not needed
Use deep sleep: 15µA vs 74mA is a 5000× improvement
Reduce LoRa TX power: 14dBm uses 25% less current than 22dBm
Lower GNSS update rate: 1Hz vs 10Hz reduces average current
PWM the display: Dimming backlight saves significant power
Batch operations: Wake, collect data, transmit, sleep