Float voltage to int (#444)

* Change voltage float to millivolt integer
* Explain the ADC to milliVolts conversion

src/components/battery/BatteryController.cpp

@@ -55,17 +55,21 @@ void Battery::SaadcInit() {
 
 void Battery::SaadcEventHandler(nrfx_saadc_evt_t const* p_event) {
 
-  const float battery_max = 4.18; // maximum voltage of battery ( max charging voltage is 4.21 )
+  const uint16_t battery_max = 4180; // maximum voltage of battery ( max charging voltage is 4.21 )
-  const float battery_min = 3.20; // minimum voltage of battery before shutdown ( depends on the battery )
+  const uint16_t battery_min = 3200; // minimum voltage of battery before shutdown ( depends on the battery )
 
   if (p_event->type == NRFX_SAADC_EVT_DONE) {
 
     APP_ERROR_CHECK(nrfx_saadc_buffer_convert(&saadc_value, 1));
 
-    voltage = (static_cast<float>(p_event->data.done.p_buffer[0]) * 2.04f) / (1024 / 3.0f);
+    // A hardware voltage divider divides the battery voltage by 2
-    voltage = roundf(voltage * 100) / 100;
+    // ADC gain is 1/5
+    // thus adc_voltage = battery_voltage / 2 * gain = battery_voltage / 10
+    // reference_voltage is 0.6V
+    // p_event->data.done.p_buffer[0] = (adc_voltage / reference_voltage) * 1024
+    voltage = p_event->data.done.p_buffer[0] * 6000 / 1024;
 
-    percentRemaining = static_cast<int>(((voltage - battery_min) / (battery_max - battery_min)) * 100);
+    percentRemaining = (voltage - battery_min) * 100 / (battery_max - battery_min);
 
     percentRemaining = std::max(percentRemaining, 0);
     percentRemaining = std::min(percentRemaining, 100);

src/components/battery/BatteryController.h

@@ -50,7 +50,7 @@ namespace Pinetime {
         return percentRemainingBuffer.GetAverage();
       }
 
-      float Voltage() const {
+      uint16_t Voltage() const {
         return voltage;
       }
 
@@ -71,7 +71,7 @@ namespace Pinetime {
       static constexpr uint32_t chargingPin = 12;
       static constexpr uint32_t powerPresentPin = 19;
       static constexpr nrf_saadc_input_t batteryVoltageAdcInput = NRF_SAADC_INPUT_AIN7;
-      float voltage = 0.0f;
+      uint16_t voltage = 0;
       int percentRemaining = -1;
 
       bool isCharging = false;

src/displayapp/screens/BatteryInfo.cpp

@@ -46,16 +46,9 @@ BatteryInfo::BatteryInfo(Pinetime::Applications::DisplayApp* app, Pinetime::Cont
   lv_label_set_align(percent, LV_LABEL_ALIGN_LEFT);
   lv_obj_align(percent, nullptr, LV_ALIGN_CENTER, 0, -60);
 
-  // hack to not use the flot functions from printf
-  uint8_t batteryVoltageBytes[2];
-  batteryVoltageBytes[1] = static_cast<uint8_t>(batteryVoltage); // truncate whole numbers
-  batteryVoltageBytes[0] =
-    static_cast<uint8_t>((batteryVoltage - batteryVoltageBytes[1]) * 100); // remove whole part of flt and shift 2 places over
-  //
-
   voltage = lv_label_create(lv_scr_act(), nullptr);
   lv_obj_set_style_local_text_color(voltage, LV_LABEL_PART_MAIN, LV_STATE_DEFAULT, lv_color_hex(0xC6A600));
-  lv_label_set_text_fmt(voltage, "%1i.%02i volts", batteryVoltageBytes[1], batteryVoltageBytes[0]);
+  lv_label_set_text_fmt(voltage, "%1i.%02i volts", batteryVoltage / 1000, batteryVoltage % 1000 / 10);
   lv_label_set_align(voltage, LV_LABEL_ALIGN_CENTER);
   lv_obj_align(voltage, nullptr, LV_ALIGN_CENTER, 0, 95);
 
@@ -129,13 +122,7 @@ void BatteryInfo::UpdateScreen() {
   }
 
   lv_obj_align(status, charging_bar, LV_ALIGN_OUT_BOTTOM_MID, 0, 20);
-  // hack to not use the flot functions from printf
+  lv_label_set_text_fmt(voltage, "%1i.%02i volts", batteryVoltage / 1000, batteryVoltage % 1000 / 10);
-  uint8_t batteryVoltageBytes[2];
-  batteryVoltageBytes[1] = static_cast<uint8_t>(batteryVoltage); // truncate whole numbers
-  batteryVoltageBytes[0] =
-    static_cast<uint8_t>((batteryVoltage - batteryVoltageBytes[1]) * 100); // remove whole part of flt and shift 2 places over
-  //
-  lv_label_set_text_fmt(voltage, "%1i.%02i volts", batteryVoltageBytes[1], batteryVoltageBytes[0]);
 }
 
 bool BatteryInfo::Refresh() {

src/displayapp/screens/BatteryInfo.h

@@ -37,7 +37,7 @@ namespace Pinetime {
 
         int8_t animation = 0;
         int8_t batteryPercent = -1;
-        float batteryVoltage = 0.0f;
+        uint16_t batteryVoltage = 0;
       };
     }
   }

src/displayapp/screens/SystemInfo.cpp

@@ -104,8 +104,6 @@ std::unique_ptr<Screen> SystemInfo::CreateScreen1() {
 
 std::unique_ptr<Screen> SystemInfo::CreateScreen2() {
   auto batteryPercent = static_cast<uint8_t>(batteryController.PercentRemaining());
-  float batteryVoltage = batteryController.Voltage();
-
   auto resetReason = [this]() {
     switch (watchdog.ResetReason()) {
       case Drivers::Watchdog::ResetReasons::Watchdog:
@@ -144,18 +142,13 @@ std::unique_ptr<Screen> SystemInfo::CreateScreen2() {
   uptimeSeconds = uptimeSeconds % secondsInAMinute;
   // TODO handle more than 100 days of uptime
 
-  // hack to not use the flot functions from printf
-  uint8_t batteryVoltageBytes[2];
-  batteryVoltageBytes[1] = static_cast<uint8_t>(batteryVoltage); // truncate whole numbers
-  batteryVoltageBytes[0] = static_cast<uint8_t>((batteryVoltage - batteryVoltageBytes[1]) * 100); // remove whole part of flt and shift 2 places over
-
   lv_obj_t* label = lv_label_create(lv_scr_act(), nullptr);
   lv_label_set_recolor(label, true);
   lv_label_set_text_fmt(label,
                         "#444444 Date# %02d/%02d/%04d\n"
                         "#444444 Time# %02d:%02d:%02d\n"
                         "#444444 Uptime#\n %02lud %02lu:%02lu:%02lu\n"
-                        "#444444 Battery# %d%%/%1i.%02iv\n"
+                        "#444444 Battery# %d%%/%03imV\n"
                         "#444444 Backlight# %s\n"
                         "#444444 Last reset# %s\n"
                         "#444444 Accel.# %s\n",
@@ -170,8 +163,7 @@ std::unique_ptr<Screen> SystemInfo::CreateScreen2() {
                         uptimeMinutes,
                         uptimeSeconds,
                         batteryPercent,
-                        batteryVoltageBytes[1],
+                        batteryController.Voltage(),
-                        batteryVoltageBytes[0],
                         brightnessController.ToString(),
                         resetReason,
                         ToString(motionController.DeviceType()));