Refactored battery measurement function

main.cpp

@@ -37,22 +37,28 @@ static CayenneLPP cayenne(51);
 
 #if MBED_CONF_APP_BATTERY_ENABLED
 AnalogIn bat(MBED_CONF_APP_BATTERY_ADC);
-AnalogIn vrefint(ADC_VREF);
+AnalogIn vref(ADC_VREF);
 
 static float battery_voltage() {
     float vbat = bat.read();
-    double vdd = (1.224f) / vrefint.read();
+    float vrefin = vref.read();
 
-    return vbat * MBED_CONF_APP_BATTERY_RATIO * vdd;
+    float vrefcal = (float)(*(uint16_t*)VREFINT_CAL_ADDR) * (1.0f / (float)0xFFF);
+    float vdda = 3.0f * vrefcal / vrefin;
+
+    return vbat * vdda * MBED_CONF_APP_BATTERY_RATIO;
 }
 
 static uint8_t battery_level() {
     float vbat = battery_voltage();
 
-    double ratio = 253.0f / (4.2f - 3.3f);
-    int value = ratio * (vbat - 3.4f) + 1.0f;
-
-    return value < 1 ? 1 : (value > 254 ? 254 : value);
+    if (vbat >= MBED_CONF_APP_BATTERY_MAX) {
+        return 254;
+    } else if (vbat > MBED_CONF_APP_BATTERY_MIN && vbat < MBED_CONF_APP_BATTERY_MAX) {
+        return ( 253 * ( vbat - MBED_CONF_APP_BATTERY_MIN ) ) / ( MBED_CONF_APP_BATTERY_MAX - MBED_CONF_APP_BATTERY_MIN ) + 1;
+    } else {
+        return 1;
+    }
 }
 #endif
 

mbed_app.json

@@ -28,6 +28,8 @@
         "battery-lpp-id":      { "value": 1 },
         "battery-in-lpp":      { "value": "false" },
         "battery-adc":         { "value": "NC" },
+        "battery-min":         { "value": "3.20f" },
+        "battery-max":         { "value": "4.15f" },
         "battery-ratio":       { "value": "2.0f" },
         "hx711-enabled":       { "value": "false" },
         "hx711-lpp-id":        { "value": 2 },