feat: battery monitoring, external RTC persistence, SD used-space fix

- Add BQ27220 fuel gauge: reads SOC percentage every 5s
- Add BQ25896 PMIC: detects charging status (pre-charge/fast/done)
- Add MAX31329 external RTC: reads time on boot, syncs from NTP
- Battery UI: icon + percentage in header, cyan when charging
- Fix SD used bytes: fallback to recursive dir walk when usedBytes() returns 0
- Libraries: PMIC_BQ25896, kode_bq27220, kode_MAX31329

platformio.ini

@@ -65,3 +65,6 @@ lib_deps =
   https://github.com/bitbank2/bb_captouch.git
   https://github.com/xreef/SimpleFTPServer.git
   bblanchon/ArduinoJson @ ^7
+  https://github.com/sqmsmu/PMIC_BQ25896.git
+  https://github.com/kodediy/kode_bq27220.git
+  https://github.com/kodediy/kode_MAX31329.git

src/main.cpp

@@ -9,6 +9,7 @@
 
 #include <Arduino.h>
 #include <WiFi.h>
+#include <Wire.h>
 #include <lvgl.h>
 #include <kodedot/display_manager.h>
 #include <kodedot/pin_config.h>
@@ -19,6 +20,9 @@
 #include <ArduinoJson.h>
 #include <SimpleFTPServer.h>
 #include <time.h>
+#include <PMIC_BQ25896.h>
+#include <BQ27220.h>
+#include <kode_MAX31329.h>
 #include "ui.h"
 
 // ---------------------------------------------------------------------------
@@ -37,6 +41,15 @@ static Adafruit_NeoPixel pixel(NEO_PIXEL_COUNT, NEO_PIXEL_PIN, NEO_GRB + NEO_KHZ
 // FTP server
 FtpServer ftpSrv;
 
+// Battery fuel gauge (BQ27220 @ 0x55)
+static BQ27220 fuelGauge;
+
+// PMIC / Charger (BQ25896 @ 0x6B)
+static PMIC_BQ25896 pmic;
+
+// External RTC (MAX31329 @ 0xD0)
+static MAX31329 rtc;
+
 // ---------------------------------------------------------------------------
 //  LED colour definitions
 // ---------------------------------------------------------------------------
@@ -53,7 +66,11 @@ static bool     sd_ok          = false;
 static bool     wifi_connected = false;
 static bool     ftp_client_on  = false;
 static bool     ftp_transfer   = false;
+static bool     rtc_ok         = false;
+static bool     gauge_ok       = false;
+static bool     pmic_ok        = false;
 static unsigned long last_time_update = 0;
+static unsigned long last_batt_update = 0;
 
 // ---------------------------------------------------------------------------
 //  NeoPixel helpers
@@ -84,10 +101,30 @@ static void updateLed() {
 // ---------------------------------------------------------------------------
 
 /** Get used / total space on SD card in MiB and push to UI */
+static uint64_t calcDirSize(fs::FS &fs, const char *dirname) {
+    uint64_t total = 0;
+    File root = fs.open(dirname);
+    if (!root || !root.isDirectory()) return 0;
+    File f = root.openNextFile();
+    while (f) {
+        if (f.isDirectory()) {
+            total += calcDirSize(fs, f.path());
+        } else {
+            total += f.size();
+        }
+        f = root.openNextFile();
+    }
+    return total;
+}
+
 static void updateSdInfo() {
     if (!sd_ok) return;
     uint64_t total = SD_MMC.totalBytes() / (1024ULL * 1024ULL);
     uint64_t used  = SD_MMC.usedBytes()  / (1024ULL * 1024ULL);
+    /* SD_MMC.usedBytes() returns 0 on exFAT / large cards — walk filesystem */
+    if (used == 0 && total > 0) {
+        used = calcDirSize(SD_MMC, "/") / (1024ULL * 1024ULL);
+    }
     ui_set_sd(used, total);
 }
 
@@ -157,6 +194,36 @@ void ftpTransferCallback(FtpTransferOperation ftpOperation, const char *name, ui
     updateLed();
 }
 
+// ---------------------------------------------------------------------------
+//  Battery monitoring
+// ---------------------------------------------------------------------------
+
+/** Update battery percentage and charging status every 5 seconds */
+static void updateBattery() {
+    unsigned long now = millis();
+    if (now - last_batt_update < 5000) return;
+    last_batt_update = now;
+
+    int soc = -1;
+    bool charging = false;
+
+    /* Read state-of-charge from fuel gauge */
+    if (gauge_ok) {
+        soc = fuelGauge.readStateOfChargePercent();
+        if (soc < 0 || soc > 100) soc = -1;  // sanity check
+    }
+
+    /* Read charging status from PMIC */
+    if (pmic_ok) {
+        pmic.setCONV_START(true);  // trigger ADC conversion
+        uint8_t chrg_stat = pmic.get_VBUS_STAT_reg().chrg_stat;
+        // chrg_stat: 0=Not Charging, 1=Pre-charge, 2=Fast Charging, 3=Charge Done
+        charging = (chrg_stat == 1 || chrg_stat == 2);
+    }
+
+    ui_set_battery(soc, charging);
+}
+
 // ---------------------------------------------------------------------------
 //  Time display
 // ---------------------------------------------------------------------------
@@ -269,6 +336,82 @@ static bool initWiFi() {
     return false;
 }
 
+/** Initialise I2C bus and battery / RTC peripherals */
+static void initPeripherals() {
+    Wire.begin(48, 47);  // SDA=48, SCL=47
+
+    /* ── Fuel Gauge (BQ27220 @ 0x55) ──────────────────────────── */
+    gauge_ok = fuelGauge.begin();
+    if (gauge_ok) {
+        int soc = fuelGauge.readStateOfChargePercent();
+        int mv  = fuelGauge.readVoltageMillivolts();
+        Serial.printf("[BAT] Fuel gauge ready — SOC: %d%%  Voltage: %d mV\n", soc, mv);
+    } else {
+        Serial.println("[BAT] Warning: BQ27220 fuel gauge not found");
+    }
+
+    /* ── PMIC (BQ25896 @ 0x6B) ───────────────────────────────── */
+    pmic.begin();
+    pmic_ok = pmic.isConnected();
+    if (pmic_ok) {
+        pmic.setCONV_START(true);  // trigger first ADC conversion
+        Serial.printf("[BAT] PMIC ready — VBUS: %d mV  VBAT: %d mV\n",
+                      pmic.getVBUSV(), pmic.getBATV());
+    } else {
+        Serial.println("[BAT] Warning: BQ25896 PMIC not found");
+    }
+
+    /* ── External RTC (MAX31329 @ 0xD0) ──────────────────────── */
+    rtc.begin();
+    /* Try reading time — if year is valid (>2020), set ESP32 system clock */
+    if (rtc.readTime()) {
+        if (rtc.t.year >= 2020 && rtc.t.year <= 2099) {
+            rtc_ok = true;
+            struct tm t = {};
+            t.tm_year = rtc.t.year - 1900;
+            t.tm_mon  = rtc.t.month - 1;
+            t.tm_mday = rtc.t.day;
+            t.tm_hour = rtc.t.hour;
+            t.tm_min  = rtc.t.minute;
+            t.tm_sec  = rtc.t.second;
+            struct timeval tv = { .tv_sec = mktime(&t), .tv_usec = 0 };
+            settimeofday(&tv, NULL);
+            Serial.printf("[RTC] External RTC time: %04d-%02d-%02d %02d:%02d:%02d\n",
+                          rtc.t.year, rtc.t.month, rtc.t.day,
+                          rtc.t.hour, rtc.t.minute, rtc.t.second);
+        } else {
+            Serial.printf("[RTC] External RTC has invalid year (%d) — will set from NTP\n", rtc.t.year);
+        }
+    } else {
+        Serial.println("[RTC] Warning: MAX31329 external RTC not responding");
+    }
+}
+
+/** Write current system time to external RTC (call after NTP sync) */
+static void syncRtcFromSystem() {
+    if (!rtc_ok && !gauge_ok) return;  // RTC not available
+
+    struct tm timeinfo;
+    if (!getLocalTime(&timeinfo, 0)) return;
+
+    rtc.t.year      = timeinfo.tm_year + 1900;
+    rtc.t.month     = timeinfo.tm_mon + 1;
+    rtc.t.day       = timeinfo.tm_mday;
+    rtc.t.hour      = timeinfo.tm_hour;
+    rtc.t.minute    = timeinfo.tm_min;
+    rtc.t.second    = timeinfo.tm_sec;
+    rtc.t.dayOfWeek = timeinfo.tm_wday;
+
+    if (rtc.writeTime()) {
+        rtc_ok = true;
+        Serial.printf("[RTC] Updated external RTC: %04d-%02d-%02d %02d:%02d:%02d\n",
+                      rtc.t.year, rtc.t.month, rtc.t.day,
+                      rtc.t.hour, rtc.t.minute, rtc.t.second);
+    } else {
+        Serial.println("[RTC] Warning: Failed to write time to external RTC");
+    }
+}
+
 /** Configure NTP with Vienna timezone and wait briefly for sync */
 static void initNtp() {
     Serial.println("[NTP] Configuring time (Vienna CET/CEST)...");
@@ -280,6 +423,8 @@ static void initNtp() {
             char buf[32];
             strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", &timeinfo);
             Serial.printf("[NTP] Time synced: %s\n", buf);
+            /* Write NTP time to external RTC for persistence */
+            syncRtcFromSystem();
             return;
         }
     }
@@ -336,6 +481,9 @@ void setup() {
     // Create the LVGL status UI
     ui_init();
 
+    // Initialise I2C peripherals (battery, RTC)
+    initPeripherals();
+
     // IO Expander — check SD card presence
     if (!checkSdPresence()) {
         Serial.println("[SD] WARNING: SD card not detected by IO expander");
@@ -388,5 +536,6 @@ void loop() {
     ftpSrv.handleFTP();
     display.update();
     updateTimeDisplay();
+    updateBattery();
     delay(5);
 }

src/ui.cpp

@@ -42,6 +42,9 @@ static lv_obj_t *lbl_time;
 static lv_obj_t *lbl_date;
 static lv_obj_t *obj_error_bar;
 static lv_obj_t *lbl_error;
+static lv_obj_t *lbl_battery;
+static lv_obj_t *obj_batt_icon;
+static lv_obj_t *obj_batt_fill;
 
 /* ── cached IP for FTP URL ───────────────────────────────────────── */
 static char cached_ip[48] = "0.0.0.0";
@@ -77,6 +80,32 @@ void ui_init()
                            LV_ALIGN_TOP_MID, 0, 16, "FTP Explorer");
     lv_obj_set_style_text_letter_space(lbl_title, 2, 0);
 
+    /* ── battery indicator (top-right) ─────────────────────────── */
+    /* battery outline (22x12 rounded rect) */
+    obj_batt_icon = lv_obj_create(scr);
+    lv_obj_set_size(obj_batt_icon, 30, 14);
+    lv_obj_set_style_radius(obj_batt_icon, 3, 0);
+    lv_obj_set_style_bg_opa(obj_batt_icon, LV_OPA_TRANSP, 0);
+    lv_obj_set_style_border_color(obj_batt_icon, lv_color_hex(CLR_GRAY), 0);
+    lv_obj_set_style_border_width(obj_batt_icon, 1, 0);
+    lv_obj_set_style_pad_all(obj_batt_icon, 2, 0);
+    lv_obj_clear_flag(obj_batt_icon, LV_OBJ_FLAG_SCROLLABLE);
+    lv_obj_align(obj_batt_icon, LV_ALIGN_TOP_RIGHT, -28, 22);
+
+    /* battery fill bar (inside the outline) */
+    obj_batt_fill = lv_obj_create(obj_batt_icon);
+    lv_obj_set_size(obj_batt_fill, 0, 8);
+    lv_obj_set_style_radius(obj_batt_fill, 1, 0);
+    lv_obj_set_style_bg_color(obj_batt_fill, lv_color_hex(CLR_GREEN), 0);
+    lv_obj_set_style_bg_opa(obj_batt_fill, LV_OPA_COVER, 0);
+    lv_obj_set_style_border_width(obj_batt_fill, 0, 0);
+    lv_obj_clear_flag(obj_batt_fill, LV_OBJ_FLAG_SCROLLABLE);
+    lv_obj_align(obj_batt_fill, LV_ALIGN_LEFT_MID, 0, 0);
+
+    /* battery percentage text */
+    lbl_battery = make_label(scr, &lv_font_montserrat_12, CLR_GRAY,
+                             LV_ALIGN_TOP_RIGHT, -62, 23, "--");
+
     /* subtle separator line */
     static lv_point_precise_t line_pts[] = {{40, 0}, {370, 0}};
     line_sep = lv_line_create(scr);
@@ -322,3 +351,37 @@ void ui_set_error(const char *msg)
         lv_obj_add_flag(obj_error_bar, LV_OBJ_FLAG_HIDDEN);
     }
 }
+
+/* ── ui_set_battery ──────────────────────────────────────────────── */
+void ui_set_battery(int pct, bool charging)
+{
+    /* pct < 0 means fuel gauge unavailable */
+    if (pct < 0) {
+        lv_label_set_text(lbl_battery, "--");
+        lv_obj_set_size(obj_batt_fill, 0, 8);
+        return;
+    }
+    if (pct > 100) pct = 100;
+
+    /* percentage label */
+    if (charging) {
+        lv_label_set_text_fmt(lbl_battery, LV_SYMBOL_CHARGE " %d%%", pct);
+        lv_obj_set_style_text_color(lbl_battery, lv_color_hex(CLR_CYAN), 0);
+    } else {
+        lv_label_set_text_fmt(lbl_battery, "%d%%", pct);
+        lv_obj_set_style_text_color(lbl_battery, lv_color_hex(CLR_GRAY), 0);
+    }
+
+    /* fill bar width: max ~22px (inner width of battery outline) */
+    int fill_w = (22 * pct) / 100;
+    if (fill_w < 1 && pct > 0) fill_w = 1;
+    lv_obj_set_size(obj_batt_fill, fill_w, 8);
+
+    /* colour: green > 20%, red <= 20%, cyan when charging */
+    uint32_t clr = CLR_GREEN;
+    if (charging)    clr = CLR_CYAN;
+    else if (pct <= 20) clr = CLR_RED;
+    lv_obj_set_style_bg_color(obj_batt_fill, lv_color_hex(clr), 0);
+    lv_obj_set_style_border_color(obj_batt_icon,
+                                  lv_color_hex(charging ? CLR_CYAN : CLR_GRAY), 0);
+}

src/ui.h

@@ -8,4 +8,5 @@ void ui_set_ftp(const char *status);
 void ui_set_time(const char *time_str);
 void ui_set_date(const char *date_str);
 void ui_set_sd(uint64_t used_mb, uint64_t total_mb);
+void ui_set_battery(int pct, bool charging);
 void ui_set_error(const char *msg);