Feature: parse additional Pylontech CAN protocol fields (#1213)

I noticed that these are missing while looking at dissassembly of the
Pytes implementation of the protocol. I also found Pylontech sample
CAN messages] which match the Pytes implementation [1]:

```
CAN ID – followed by 2 to 8 bytes of data:
0x351 – 14 02 74 0E 74 0E CC 01 – Battery voltage + current limits
                          ^^^^^ discharge cutoff voltage 46.0V
0x355 – 1A 00 64 00 – State of Health (SOH) / State of Charge (SOC)
0x356 – 4e 13 02 03 04 05 – Voltage / Current / Temp
0x359 – 00 00 00 00 0A 50 4E – Protection & Alarm flags
                       ^^^^^ always 0x50 0x59 in Pytes implementation
                    ^^ module count (matches the blog article image)
0x35C – C0 00 – Battery charge request flags
        ^^ two possible additional flags (bit 3 and bit 4)
0x35E – 50 59 4C 4F 4E 20 20 20 – Manufacturer name (“PYLON “)
        ^^^^^^^^^^^^^^ Note: Pytes sends a 5-byte message "PYTES" instead
                       padding with spaces
```

The extra charge request flag is "bit4: SOC low" (Seems to be SoC < 10%
threshold for Pytes), I haven't bothered adding that as it provides
little value.

[1] https://www.setfirelabs.com/green-energy/pylontech-can-reading-can-replication

include/BatteryStats.h

@@ -118,6 +118,7 @@ class PylontechBatteryStats : public BatteryStats {
 
         float _chargeVoltage;
         float _chargeCurrentLimitation;
+        float _dischargeVoltageLimitation;
         uint16_t _stateOfHealth;
         float _temperature;
 
@@ -140,6 +141,8 @@ class PylontechBatteryStats : public BatteryStats {
         bool _chargeEnabled;
         bool _dischargeEnabled;
         bool _chargeImmediately;
+
+        uint8_t _moduleCount;
 };
 
 class SBSBatteryStats : public BatteryStats {

src/BatteryStats.cpp

@@ -124,8 +124,10 @@ void PylontechBatteryStats::getLiveViewData(JsonVariant& root) const
     // values go into the "Status" card of the web application
     addLiveViewValue(root, "chargeVoltage", _chargeVoltage, "V", 1);
     addLiveViewValue(root, "chargeCurrentLimitation", _chargeCurrentLimitation, "A", 1);
+    addLiveViewValue(root, "dischargeVoltageLimitation", _dischargeVoltageLimitation, "V", 1);
     addLiveViewValue(root, "stateOfHealth", _stateOfHealth, "%", 0);
     addLiveViewValue(root, "temperature", _temperature, "°C", 1);
+    addLiveViewValue(root, "modules", _moduleCount, "", 0);
 
     addLiveViewTextValue(root, "chargeEnabled", (_chargeEnabled?"yes":"no"));
     addLiveViewTextValue(root, "dischargeEnabled", (_dischargeEnabled?"yes":"no"));
@@ -380,6 +382,7 @@ void PylontechBatteryStats::mqttPublish() const
 
     MqttSettings.publish("battery/settings/chargeVoltage", String(_chargeVoltage));
     MqttSettings.publish("battery/settings/chargeCurrentLimitation", String(_chargeCurrentLimitation));
+    MqttSettings.publish("battery/settings/dischargeVoltageLimitation", String(_dischargeVoltageLimitation));
     MqttSettings.publish("battery/stateOfHealth", String(_stateOfHealth));
     MqttSettings.publish("battery/temperature", String(_temperature));
     MqttSettings.publish("battery/alarm/overCurrentDischarge", String(_alarmOverCurrentDischarge));
@@ -399,6 +402,7 @@ void PylontechBatteryStats::mqttPublish() const
     MqttSettings.publish("battery/charging/chargeEnabled", String(_chargeEnabled));
     MqttSettings.publish("battery/charging/dischargeEnabled", String(_dischargeEnabled));
     MqttSettings.publish("battery/charging/chargeImmediately", String(_chargeImmediately));
+    MqttSettings.publish("battery/modulesTotal", String(_moduleCount));
 }
 
 void SBSBatteryStats::mqttPublish() const

src/MqttHandleBatteryHass.cpp

@@ -55,7 +55,9 @@ void MqttHandleBatteryHassClass::loop()
             publishSensor("State of Health (SOH)", "mdi:heart-plus", "stateOfHealth", NULL, "measurement", "%");
             publishSensor("Charge voltage (BMS)", NULL, "settings/chargeVoltage", "voltage", "measurement", "V");
             publishSensor("Charge current limit", NULL, "settings/chargeCurrentLimitation", "current", "measurement", "A");
+            publishSensor("Discharge voltage limit", NULL, "settings/dischargeVoltageLimitation", "voltage", "measurement", "V");
             publishSensor("Discharge current limit", NULL, "settings/dischargeCurrentLimitation", "current", "measurement", "A");
+            publishSensor("Module Count", "mdi:counter", "modulesTotal");
 
             publishBinarySensor("Alarm Discharge current", "mdi:alert", "alarm/overCurrentDischarge", "1", "0");
             publishBinarySensor("Warning Discharge current", "mdi:alert-outline", "warning/highCurrentDischarge", "1", "0");

src/PylontechCanReceiver.cpp

@@ -18,10 +18,12 @@ void PylontechCanReceiver::onMessage(twai_message_t rx_message)
             _stats->_chargeVoltage = this->scaleValue(this->readUnsignedInt16(rx_message.data), 0.1);
             _stats->_chargeCurrentLimitation = this->scaleValue(this->readSignedInt16(rx_message.data + 2), 0.1);
             _stats->setDischargeCurrentLimit(this->scaleValue(this->readSignedInt16(rx_message.data + 4), 0.1), millis());
+            _stats->_dischargeVoltageLimitation = this->scaleValue(this->readUnsignedInt16(rx_message.data + 6), 0.1);
 
             if (_verboseLogging) {
-                MessageOutput.printf("[Pylontech] chargeVoltage: %f chargeCurrentLimitation: %f dischargeCurrentLimitation: %f\r\n",
+                MessageOutput.printf("[Pylontech] chargeVoltage: %f chargeCurrentLimitation: %f dischargeCurrentLimitation: %f dischargeVoltageLimitation: %f\r\n",
-                        _stats->_chargeVoltage, _stats->_chargeCurrentLimitation, _stats->getDischargeCurrentLimit());
+                        _stats->_chargeVoltage, _stats->_chargeCurrentLimitation, _stats->getDischargeCurrentLimit(),
+                        _stats->_dischargeVoltageLimitation);
             }
             break;
         }
@@ -93,6 +95,13 @@ void PylontechCanReceiver::onMessage(twai_message_t rx_message)
                         _stats->_warningBmsInternal,
                         _stats->_warningHighCurrentCharge);
             }
+
+            _stats->_moduleCount = rx_message.data[4];
+            if (_verboseLogging) {
+                MessageOutput.printf("[Pylontech] Modules: %d\r\n",
+                        _stats->_moduleCount);
+            }
+
             break;
         }
 
@@ -155,6 +164,7 @@ void PylontechCanReceiver::dummyData()
     _stats->_chargeVoltage = dummyFloat(50);
     _stats->_chargeCurrentLimitation = dummyFloat(33);
     _stats->setDischargeCurrentLimit(dummyFloat(12), millis());
+    _stats->_dischargeVoltageLimitation = dummyFloat(46);
     _stats->_stateOfHealth = 99;
     _stats->setVoltage(48.67, millis());
     _stats->setCurrent(dummyFloat(-1), 1/*precision*/, millis());
@@ -164,6 +174,8 @@ void PylontechCanReceiver::dummyData()
     _stats->_dischargeEnabled = true;
     _stats->_chargeImmediately = false;
 
+    _stats->_moduleCount = 1;
+
     _stats->_warningHighCurrentDischarge = false;
     _stats->_warningHighCurrentCharge = false;
     _stats->_warningLowTemperature = false;