battery percentage calculation improved

include/power.h

@@ -7,6 +7,7 @@
 
 #include "i2c.h"
 #include "reset.h"
+#include "lorawan.h"
 
 #define DEFAULT_VREF 1100 // tbd: use adc2_vref_to_gpio() for better estimate
 #define NO_OF_SAMPLES 64  // we do some multisampling to get better values
@@ -15,11 +16,12 @@
 #define BAT_MAX_VOLTAGE 4200 // millivolts
 #endif
 #ifndef BAT_MIN_VOLTAGE
-#define BAT_MIN_VOLTAGE 2800 // millivolts
+#define BAT_MIN_VOLTAGE 3100 // millivolts
 #endif
 
+typedef uint8_t (*mapFn_t)(uint16_t, uint16_t, uint16_t);
+
 uint16_t read_voltage(void);
-uint8_t read_battlevel(void);
 void calibrate_voltage(void);
 bool batt_sufficient(void);
 
@@ -34,4 +36,67 @@ void AXP192_showstatus(void);
 
 #endif // HAS_PMU
 
+// The following map functions were taken from
+
+/*
+ Battery.h - Battery library
+ Copyright (c) 2014 Roberto Lo Giacco.
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as 
+ published by the Free Software Foundation, either version 3 of the 
+ License, or (at your option) any later version.
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+ You should have received a copy of the GNU General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+//
+// Plots of the functions below available at
+// https://www.desmos.com/calculator/x0esk5bsrk
+//
+
+/**
+ * Symmetric sigmoidal approximation
+ * https://www.desmos.com/calculator/7m9lu26vpy
+ *
+ * c - c / (1 + k*x/v)^3
+ */
+static inline uint8_t sigmoidal(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
+	// slow
+	// uint8_t result = 110 - (110 / (1 + pow(1.468 * (voltage - minVoltage)/(maxVoltage - minVoltage), 6)));
+
+	// steep
+	// uint8_t result = 102 - (102 / (1 + pow(1.621 * (voltage - minVoltage)/(maxVoltage - minVoltage), 8.1)));
+
+	// normal
+	uint8_t result = 105 - (105 / (1 + pow(1.724 * (voltage - minVoltage)/(maxVoltage - minVoltage), 5.5)));
+	return result >= 100 ? 100 : result;
+}
+
+/**
+ * Asymmetric sigmoidal approximation
+ * https://www.desmos.com/calculator/oyhpsu8jnw
+ *
+ * c - c / [1 + (k*x/v)^4.5]^3
+ */
+static inline uint8_t asigmoidal(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
+	uint8_t result = 101 - (101 / pow(1 + pow(1.33 * (voltage - minVoltage)/(maxVoltage - minVoltage) ,4.5), 3));
+	return result >= 100 ? 100 : result;
+}
+
+/**
+ * Linear mapping
+ * https://www.desmos.com/calculator/sowyhttjta
+ *
+ * x * 100 / v
+ */
+static inline uint8_t linear(uint16_t voltage, uint16_t minVoltage, uint16_t maxVoltage) {
+	return (unsigned long)(voltage - minVoltage) * 100 / (maxVoltage - minVoltage);
+}
+
+uint8_t read_battlevel(mapFn_t mapFunction = &sigmoidal);
+
 #endif

src/cyclic.cpp

@@ -68,10 +68,6 @@ void doHousekeeping() {
 #if (defined BAT_MEASURE_ADC || defined HAS_PMU)
   batt_level = read_battlevel();
   ESP_LOGI(TAG, "Battery: %d%%", batt_level);
-#if (HAS_LORA)
-  // to come with future LMIC version
-  // lora_setBattLevel(batt_level);
-#endif
 #ifdef HAS_PMU
   AXP192_showstatus();
 #endif

src/lorawan.cpp

@@ -485,12 +485,10 @@ void lora_setBattLevel(uint8_t batt_percent) {
 #endif // HAS_PMU
 
   else
-    lmic_batt_level = static_cast<uint8_t>(
-        (float)batt_percent /
-        (float)(MCMD_DEVS_BATT_MAX - MCMD_DEVS_BATT_MIN + 1) * 100.0f);
+    lmic_batt_level =
+        batt_percent / 100.0 * (MCMD_DEVS_BATT_MAX - MCMD_DEVS_BATT_MIN + 1);
 
   LMIC_setBattLevel(lmic_batt_level);
-  ESP_LOGD(TAG, "lmic_batt_level = %d", lmic_batt_level);
 }
 
 // event EV_RXCOMPLETE message handler

src/power.cpp

@@ -210,19 +210,29 @@ uint16_t read_voltage(void) {
   return voltage;
 }
 
-uint8_t read_battlevel() {
+uint8_t read_battlevel(mapFn_t mapFunction) {
 
-  // return the battery level in values 0 ... 255 [percent],
-  // values > 100 probably mean external power, depending on hardware
+  // returns the estimated battery level in values 0 ... 100 [percent],
 
   const uint16_t batt_voltage = read_voltage();
-  float batt_percent_fl = (float)(batt_voltage - BAT_MIN_VOLTAGE) /
-                          (float)(BAT_MAX_VOLTAGE - BAT_MIN_VOLTAGE) * 100.0f;
-  const uint8_t batt_percent = static_cast<uint8_t>(batt_percent_fl);
+  uint8_t batt_percent;
 
-  ESP_LOGD(TAG, "batt_voltage = %dmV / batt_percent = %u%%", batt_voltage,
+  if (batt_voltage <= BAT_MIN_VOLTAGE)
+    batt_percent = 0;
+  else if (batt_voltage >= BAT_MAX_VOLTAGE)
+    batt_percent = 100;
+  else
+    batt_percent =
+        (*mapFunction)(batt_voltage, BAT_MIN_VOLTAGE, BAT_MAX_VOLTAGE);
+
+  ESP_LOGD(TAG, "batt_voltage = %dmV / batt_percent = %d%%", batt_voltage,
            batt_percent);
 
+#if (HAS_LORA)
+  // to come with future LMIC version
+  // lora_setBattLevel(batt_percent);
+#endif
+
   return batt_percent;
 }