DPL config: round floats and convert to double

this seems to be the only way to force ArduinoJson to serialize the
value in the way we expect, i.e., with only the amount of decimal digits
that the value can actually provide as precision.

src/Configuration.cpp

@@ -84,6 +84,18 @@ void ConfigurationClass::serializePowerLimiterConfig(PowerLimiterConfig const& s
         return String(serialBuffer);
     };
 
+    // we want a representation of our floating-point value in the JSON that
+    // uses the least amount of decimal digits possble to convey the value that
+    // is actually represented by the float. this is no easy task. ArduinoJson
+    // does this for us, however, it does it as expected only for variables of
+    // type double. this is probably because it assumes all floating-point
+    // values to have the precision of a double (64 bits), so it prints the
+    // respective number of siginificant decimals, which are too many if the
+    // actual value is a float (32 bits).
+    auto roundedFloat = [](float val) -> double {
+        return static_cast<int>(val * 100 + 0.5) / 100.0;
+    };
+
     target["enabled"] = source.Enabled;
     target["verbose_logging"] = source.VerboseLogging;
     target["solar_passthrough_enabled"] = source.SolarPassThroughEnabled;
@@ -95,12 +107,12 @@ void ConfigurationClass::serializePowerLimiterConfig(PowerLimiterConfig const& s
     target["ignore_soc"] = source.IgnoreSoc;
     target["battery_soc_start_threshold"] = source.BatterySocStartThreshold;
     target["battery_soc_stop_threshold"] = source.BatterySocStopThreshold;
-    target["voltage_start_threshold"] = source.VoltageStartThreshold;
-    target["voltage_stop_threshold"] = source.VoltageStopThreshold;
+    target["voltage_start_threshold"] = roundedFloat(source.VoltageStartThreshold);
+    target["voltage_stop_threshold"] = roundedFloat(source.VoltageStopThreshold);
     target["voltage_load_correction_factor"] = source.VoltageLoadCorrectionFactor;
     target["full_solar_passthrough_soc"] = source.FullSolarPassThroughSoc;
-    target["full_solar_passthrough_start_voltage"] = source.FullSolarPassThroughStartVoltage;
-    target["full_solar_passthrough_stop_voltage"] = source.FullSolarPassThroughStopVoltage;
+    target["full_solar_passthrough_start_voltage"] = roundedFloat(source.FullSolarPassThroughStartVoltage);
+    target["full_solar_passthrough_stop_voltage"] = roundedFloat(source.FullSolarPassThroughStopVoltage);
     target["inverter_serial_for_dc_voltage"] = serialStr(source.InverterSerialForDcVoltage);
     target["inverter_channel_id_for_dc_voltage"] = source.InverterChannelIdForDcVoltage;
     target["inverter_restart_hour"] = source.RestartHour;