Add JBD BMS cell voltage telemetry

modified:   firmware/esp32/xterra-controller/bms.cpp
	modified:   firmware/esp32/xterra-controller/bms.h
	modified:   firmware/esp32/xterra-controller/xterra-controller.ino

firmware/esp32/xterra-controller/bms.cpp

@@ -25,6 +25,10 @@ static uint8_t JBD_STATUS_REQUEST[] = {
     0xDD, 0xA5, 0x03, 0x00, 0xFF, 0xFD, 0x77
 };
 
+static uint8_t JBD_CELL_REQUEST[] = {
+    0xDD, 0xA5, 0x04, 0x00, 0xFF, 0xFC, 0x77
+};
+
 static uint16_t readU16(const uint8_t* data, int index) {
     return ((uint16_t)data[index] << 8) | data[index + 1];
 }
@@ -36,6 +40,7 @@ static int16_t readS16(const uint8_t* data, int index) {
 static void resetResponseBuffer() {
     responseLength = 0;
     responseReady = false;
+    memset(responseBuffer, 0, sizeof(responseBuffer));
 }
 
 static void handleNotify(
@@ -104,14 +109,37 @@ static bool connectBms() {
     return true;
 }
 
+static bool requestPacket(uint8_t* command, size_t commandLength) {
+    resetResponseBuffer();
+
+    bool ok = writeChar->writeValue(command, commandLength, false);
+    if (!ok) {
+        Serial.println("BMS: Write failed");
+        bmsData.connected = false;
+        return false;
+    }
+
+    unsigned long start = millis();
+    while (!responseReady && millis() - start < 2000) {
+        delay(10);
+    }
+
+    if (!responseReady) {
+        Serial.println("BMS: Read timeout");
+        return false;
+    }
+
+    return true;
+}
+
 static bool parseBasicInfo() {
     if (responseLength < 40) {
-        Serial.println("BMS: Response too short");
+        Serial.println("BMS: Basic response too short");
         return false;
     }
 
     if (responseBuffer[0] != 0xDD || responseBuffer[1] != 0x03) {
-        Serial.println("BMS: Unexpected response header");
+        Serial.println("BMS: Unexpected basic response header");
         return false;
     }
 
@@ -122,12 +150,12 @@ static bool parseBasicInfo() {
     uint16_t cyclesRaw = readU16(responseBuffer, 12);
 
     uint8_t socRaw = responseBuffer[23];
-    uint8_t mosTempAndCellOffset = 24;
 
-    uint8_t cellCount = responseBuffer[mosTempAndCellOffset + 1];
-    uint8_t ntcCount = responseBuffer[mosTempAndCellOffset + 2];
+    uint8_t offset = 24;
+    uint8_t cellCount = responseBuffer[offset + 1];
+    uint8_t ntcCount = responseBuffer[offset + 2];
 
-    int tempOffset = mosTempAndCellOffset + 3;
+    int tempOffset = offset + 3;
     float tempF = 0;
 
     if (ntcCount > 0 && responseLength > (size_t)(tempOffset + 1)) {
@@ -159,6 +187,66 @@ static bool parseBasicInfo() {
     return true;
 }
 
+static bool parseCellVoltages() {
+    if (responseLength < 7) {
+        Serial.println("BMS: Cell response too short");
+        return false;
+    }
+
+    if (responseBuffer[0] != 0xDD || responseBuffer[1] != 0x04) {
+        Serial.println("BMS: Unexpected cell response header");
+        return false;
+    }
+
+    uint8_t payloadLength = responseBuffer[3];
+    int cellsReported = payloadLength / 2;
+
+    if (cellsReported > BMS_MAX_CELLS) {
+        cellsReported = BMS_MAX_CELLS;
+    }
+
+    if (cellsReported <= 0) {
+        Serial.println("BMS: No cell voltages reported");
+        return false;
+    }
+
+    float minV = 99.0;
+    float maxV = 0.0;
+
+    for (int i = 0; i < cellsReported; i++) {
+        uint16_t mv = readU16(responseBuffer, 4 + (i * 2));
+        float volts = mv / 1000.0;
+
+        bmsData.cellVoltages[i] = volts;
+
+        if (volts < minV) {
+            minV = volts;
+        }
+
+        if (volts > maxV) {
+            maxV = volts;
+        }
+    }
+
+    bmsData.cellCount = cellsReported;
+    bmsData.cellMinVoltage = minV;
+    bmsData.cellMaxVoltage = maxV;
+    bmsData.cellDeltaMv = (int)((maxV - minV) * 1000.0 + 0.5);
+    bmsData.cellsValid = true;
+
+    Serial.print("BMS: Cells ");
+    Serial.print(cellsReported);
+    Serial.print(", min ");
+    Serial.print(minV, 3);
+    Serial.print("V, max ");
+    Serial.print(maxV, 3);
+    Serial.print("V, delta ");
+    Serial.print(bmsData.cellDeltaMv);
+    Serial.println("mV");
+
+    return true;
+}
+
 void initBms() {
     NimBLEDevice::init("XterraESP32");
     NimBLEDevice::setPower(ESP_PWR_LVL_P9);
@@ -176,29 +264,13 @@ void updateBms() {
         return;
     }
 
-    resetResponseBuffer();
-
-    bool ok = writeChar->writeValue(
-        JBD_STATUS_REQUEST,
-        sizeof(JBD_STATUS_REQUEST),
-        false
-    );
-
-    if (!ok) {
-        Serial.println("BMS: Write failed");
-        bmsData.connected = false;
-        return;
+    if (requestPacket(JBD_STATUS_REQUEST, sizeof(JBD_STATUS_REQUEST))) {
+        parseBasicInfo();
     }
 
-    unsigned long start = millis();
-    while (!responseReady && millis() - start < 2000) {
-        delay(10);
-    }
+    delay(100);
 
-    if (!responseReady) {
-        Serial.println("BMS: Read timeout");
-        return;
+    if (requestPacket(JBD_CELL_REQUEST, sizeof(JBD_CELL_REQUEST))) {
+        parseCellVoltages();
     }
-
-    parseBasicInfo();
 }

firmware/esp32/xterra-controller/bms.h

@@ -1,8 +1,11 @@
 #pragma once
 
+#define BMS_MAX_CELLS 8
+
 struct BmsData {
     bool connected = false;
     bool valid = false;
+    bool cellsValid = false;
 
     float soc = 0;
     float voltage = 0;
@@ -14,6 +17,11 @@ struct BmsData {
     int cycleCount = 0;
     int cellCount = 0;
     int ntcCount = 0;
+
+    float cellVoltages[BMS_MAX_CELLS] = {0};
+    float cellMinVoltage = 0;
+    float cellMaxVoltage = 0;
+    int cellDeltaMv = 0;
 };
 
 extern BmsData bmsData;

firmware/esp32/xterra-controller/xterra-controller.ino

@@ -45,6 +45,17 @@ void buildStatusDocument(JsonDocument& doc) {
         battery["cycle_count"] = bmsData.cycleCount;
         battery["cell_count"] = bmsData.cellCount;
         battery["ntc_count"] = bmsData.ntcCount;
+
+        JsonArray cells = battery.createNestedArray("cell_voltages");
+        if (bmsData.cellsValid) {
+            for (int i = 0; i < bmsData.cellCount; i++) {
+                cells.add(bmsData.cellVoltages[i]);
+            }
+        }
+
+        battery["cell_min_voltage"] = bmsData.cellMinVoltage;
+        battery["cell_max_voltage"] = bmsData.cellMaxVoltage;
+        battery["cell_delta_mv"] = bmsData.cellDeltaMv;
     } else {
         battery["source"] = "placeholder";
         battery["connected"] = false;