Merge branch 'main' of github.com:joeycastillo/Sensor-Watch into main

12 files changed, 475 insertions, 19 deletions

diff --git a/movement/make/Makefile b/movement/make/Makefile
index a937222b..b595d2dd 100755
--- a/movement/make/Makefile
+++ b/movement/make/Makefile
@@ -33,7 +33,10 @@ SRCS += \
   ../watch_faces/thermistor/thermistor_readout_face.c \
   ../watch_faces/thermistor/thermistor_logging_face.c \
   ../watch_faces/demos/character_set_face.c \
+  ../watch_faces/demos/voltage_face.c \
   ../watch_faces/complications/beats_face.c \
+  ../watch_faces/complications/day_one_face.c \
+  ../watch_faces/complications/stopwatch_face.c \
 
 # Leave this line at the bottom of the file; it has all the targets for making your project.
 include $(TOP)/rules.mk
diff --git a/movement/movement.c b/movement/movement.c
index 5622f17f..797e75bf 100644
--- a/movement/movement.c
+++ b/movement/movement.c
@@ -105,7 +105,7 @@ void app_setup() {
             watch_faces[i].setup(&movement_state.settings, &watch_face_contexts[i]);
         }
 
-        watch_faces[0].activate(&movement_state.settings, watch_face_contexts[0]);
+        watch_faces[movement_state.current_watch_face].activate(&movement_state.settings, watch_face_contexts[movement_state.current_watch_face]);
         event.subsecond = 0;
         event.event_type = EVENT_ACTIVATE;
     }
@@ -143,11 +143,6 @@ bool app_loop() {
         }
     }
 
-    // if we have timed out of our timeout countdown, give the app a hint that they can resign.
-    if (movement_state.timeout_ticks == 0) {
-        event.event_type = EVENT_TIMEOUT;
-    }
-
     // handle background tasks, if the alarm handler told us we need to
     if (movement_state.needs_background_tasks_handled) _movement_handle_background_tasks();
 
@@ -181,9 +176,18 @@ bool app_loop() {
         event.subsecond = movement_state.subsecond;
         can_sleep = watch_faces[movement_state.current_watch_face].loop(event, &movement_state.settings, watch_face_contexts[movement_state.current_watch_face]);
         event.event_type = EVENT_NONE;
-        event.subsecond = 0;
     }
 
+    // if we have timed out of our timeout countdown, give the app a hint that they can resign.
+    if (movement_state.timeout_ticks == 0) {
+        event.event_type = EVENT_TIMEOUT;
+        event.subsecond = movement_state.subsecond;
+        watch_faces[movement_state.current_watch_face].loop(event, &movement_state.settings, watch_face_contexts[movement_state.current_watch_face]);
+        event.event_type = EVENT_NONE;
+    }
+
+    event.subsecond = 0;
+
     return can_sleep && !movement_state.led_on;
 }
 
diff --git a/movement/movement.h b/movement/movement.h
index cb162b95..6953549a 100644
--- a/movement/movement.h
+++ b/movement/movement.h
@@ -3,27 +3,77 @@
 #include <stdio.h>
 #include <stdbool.h>
 
-// TODO: none of this is implemented
+// Movement Preferences
+// These four 32-bit structs store information about the wearer and their preferences. Tentatively, the plan is
+// for Movement to use four 32-bit registers for these preferences and to store them in the RTC's backup registers
+// 0-3, leaving registers 4-7 available for third party watch faces to use as they see fit.
+// * The movement_settings_t struct is provided to all watch faces in the callback functions, and will eventually
+//   be stored in the RTC's first backup register (BKUP[0]).
+// * The movement_location_t and movement_birthdate_t types are defined here, and are tentatively meant to be
+//   stored in BKUP[1] and BKUP[2], respectively.
+// * The movement_reserved_t type is here as a placeholder, because I sense there's some other generally useful
+//   stuff we'll want to make available to all watch faces and stash in the BKUP[3] register.
+// Anyway: Eventually, if Movement supports the BACKUP sleep mode, this will allow these preferences to be stored
+// before entering BACKUP mode and and restored after waking from reset.
+
+// movement_settings_t contains global settings that cover watch behavior, including preferences around clock and unit
+// display, time zones, buzzer behavior, LED color and low energy mode timeouts.
+// Eventually it will be stored in BKUP[0] when Movement enters BACKUP mode.
 typedef union {
     struct {
-        uint32_t reserved : 14;
-        uint32_t button_should_sound : 1;   // if true, pressing a button emits a sound.
-        uint32_t to_interval : 2;           // an inactivity interval for asking the active face to resign.
-        uint32_t le_interval : 3;           // 0 to disable low energy mode, or an inactivity interval for going into low energy mode.
-        uint32_t led_duration : 2;          // how many seconds to shine the LED for (x2), or 0 to disable it.
-        uint32_t led_red_color : 4;         // for general purpose illumination, the red LED value (0-15)
-        uint32_t led_green_color : 4;       // for general purpose illumination, the green LED value (0-15)
+        bool button_should_sound : 1;       // if true, pressing a button emits a sound.
+        uint8_t to_interval : 2;            // an inactivity interval for asking the active face to resign.
+        uint8_t le_interval : 3;            // 0 to disable low energy mode, or an inactivity interval for going into low energy mode.
+        uint8_t led_duration : 2;           // how many seconds to shine the LED for (x2), or 0 to disable it.
+        uint8_t led_red_color : 4;          // for general purpose illumination, the red LED value (0-15)
+        uint8_t led_green_color : 4;        // for general purpose illumination, the green LED value (0-15)
+        uint8_t time_zone : 6;              // TODO: an integer representing an index in the (to be implemented) time zone table.
 
         // while Movement itself doesn't implement a clock or display units, it may make sense to include some
         // global settings for watch faces to check. The 12/24 hour preference could inform a clock or a
         // time-oriented complication like a sunrise/sunset timer, and a simple locale preference could tell an
         // altimeter to display feet or meters as easily as it tells a thermometer to display degrees in F or C.
-        uint32_t clock_mode_24h : 1;        // indicates whether clock should use 12 or 24 hour mode.
-        uint32_t use_imperial_units : 1;    // indicates whether to use metric units (the default) or imperial.
+        bool clock_mode_24h : 1;            // indicates whether clock should use 12 or 24 hour mode.
+        bool use_imperial_units : 1;        // indicates whether to use metric units (the default) or imperial.
+        uint8_t reserved : 8;               // room for more preferences if needed.
     } bit;
-    uint32_t value;
+    uint32_t reg;
 } movement_settings_t;
 
+// movement_location_t is for storing the wearer's location. This will be useful for astronomical calculations such as
+// sunrise and sunset, or predictions of visible satellite passes.
+// If you create a UI for this register or need to access it, look for it in the RTC's BKUP[1] register.
+typedef union {
+    struct {
+        int16_t latitude : 16;   // signed latutide in hundredths of a degree
+        int16_t longitude : 16;  // signed longitude in hundredths of a degree
+    } bit;
+    uint32_t reg;
+} movement_location_t;
+
+// movement_birthdate_t is for storing the user's birth date. This will be useful for calculating the user's age — or
+// hey, playing happy birthday at midnight? Fields for birth time (with hour and minute resolution) are also available,
+// partly because they fit so nicely, but also because they can be useful for certain astrological calculations.
+// If you create a UI for birth date or need to access it, look for it in the RTC's BKUP[2] register.
+typedef union {
+    struct {
+        uint16_t year : 12;  // good through the year 4095
+        uint8_t month : 4;
+        uint8_t day : 5;
+        uint8_t hour : 5;
+        uint8_t minute : 6;
+    } bit;
+    uint32_t reg;
+} movement_birthdate_t;
+
+// movement_reserved_t is a placeholder for future use of the BKUP[3] register.
+typedef union {
+    struct {
+        uint32_t reserved : 32;
+    } bit;
+    uint32_t reg;
+} movement_reserved_t;
+
 typedef enum {
     EVENT_NONE = 0,             // There is no event to report.
     EVENT_ACTIVATE,             // Your watch face is entering the foreground.
diff --git a/movement/movement_config.h b/movement/movement_config.h
index 3e911477..fa5ddf18 100644
--- a/movement/movement_config.h
+++ b/movement/movement_config.h
@@ -9,6 +9,9 @@
 #include "thermistor_logging_face.h"
 #include "character_set_face.h"
 #include "beats_face.h"
+#include "day_one_face.h"
+#include "voltage_face.h"
+#include "stopwatch_face.h"
 
 const watch_face_t watch_faces[] = {
     simple_clock_face,
diff --git a/movement/watch_faces/clock/simple_clock_face.c b/movement/watch_faces/clock/simple_clock_face.c
index 9e279d95..72f7713f 100644
--- a/movement/watch_faces/clock/simple_clock_face.c
+++ b/movement/watch_faces/clock/simple_clock_face.c
@@ -28,7 +28,6 @@ bool simple_clock_face_loop(movement_event_t event, movement_settings_t *setting
     switch (event.event_type) {
         case EVENT_ACTIVATE:
         case EVENT_TICK:
-        case EVENT_TIMEOUT:
         case EVENT_LOW_ENERGY_UPDATE:
             date_time = watch_rtc_get_date_time();
             previous_date_time = *((uint32_t *)context);
diff --git a/movement/watch_faces/complications/beats_face.c b/movement/watch_faces/complications/beats_face.c
index 73a82719..95a9aaef 100644
--- a/movement/watch_faces/complications/beats_face.c
+++ b/movement/watch_faces/complications/beats_face.c
@@ -26,6 +26,7 @@ bool beats_face_loop(movement_event_t event, movement_settings_t *settings, void
 
     watch_date_time date_time;
     switch (event.event_type) {
+        case EVENT_ACTIVATE:
         case EVENT_TICK:
             date_time = watch_rtc_get_date_time();
             beats = clock2beats(date_time.unit.hour, date_time.unit.minute, date_time.unit.second, event.subsecond, UTC_OFFSET);
@@ -34,6 +35,7 @@ bool beats_face_loop(movement_event_t event, movement_settings_t *settings, void
             watch_display_string(buf, 0);
             break;
         case EVENT_LOW_ENERGY_UPDATE:
+            if (!watch_tick_animation_is_running()) watch_start_tick_animation(432);
             date_time = watch_rtc_get_date_time();
             beats = clock2beats(date_time.unit.hour, date_time.unit.minute, date_time.unit.second, event.subsecond, UTC_OFFSET);
             sprintf(buf, "bt  %4d  ", (int)beats);
diff --git a/movement/watch_faces/complications/day_one_face.c b/movement/watch_faces/complications/day_one_face.c
new file mode 100644
index 00000000..146f3f6f
--- /dev/null
+++ b/movement/watch_faces/complications/day_one_face.c
@@ -0,0 +1,177 @@
+#include <stdlib.h>
+#include <string.h>
+#include "day_one_face.h"
+#include "watch.h"
+
+uint32_t _day_one_face_juliandaynum(uint16_t year, uint16_t month, uint16_t day) {
+    // from here: https://en.wikipedia.org/wiki/Julian_day#Julian_day_number_calculation
+    return (1461 * (year + 4800 + (month - 14) / 12)) / 4 + (367 * (month - 2 - 12 * ((month - 14) / 12))) / 12 - (3 * ((year + 4900 + (month - 14) / 12) / 100))/4 + day - 32075;
+}
+
+void _day_one_face_update(day_one_state_t state) {
+    char buf[14];
+    watch_date_time date_time = watch_rtc_get_date_time();
+    uint32_t julian_date = _day_one_face_juliandaynum(date_time.unit.year + WATCH_RTC_REFERENCE_YEAR, date_time.unit.month, date_time.unit.day);
+    uint32_t julian_birthdate = _day_one_face_juliandaynum(state.birth_year, state.birth_month, state.birth_day);
+    sprintf(buf, "DA  %6ld", julian_date - julian_birthdate);
+    watch_display_string(buf, 0);
+}
+
+void day_one_face_setup(movement_settings_t *settings, void ** context_ptr) {
+    (void) settings;
+    if (*context_ptr == NULL) {
+        *context_ptr = malloc(sizeof(day_one_state_t));
+        memset(*context_ptr, 0, sizeof(day_one_state_t));
+        movement_birthdate_t movement_birthdate = (movement_birthdate_t) watch_get_backup_data(2);
+        if (movement_birthdate.reg == 0) {
+            // if birth date is totally blank, set a reasonable starting date. this works well for anyone under 63, but
+            // you can keep pressing to go back to 1900; just pass the current year. also picked this date because if you
+            // set it to 1959-01-02, it counts up from the launch of Luna-1, the first spacecraft to leave the well.
+            movement_birthdate.bit.year = 1959;
+            movement_birthdate.bit.month = 1;
+            movement_birthdate.bit.day = 1;
+            watch_store_backup_data(movement_birthdate.reg, 2);
+        }
+    }
+}
+
+void day_one_face_activate(movement_settings_t *settings, void *context) {
+    (void) settings;
+    day_one_state_t *state = (day_one_state_t *)context;
+
+    // stash the current year, useful in birthday setting mode.
+    watch_date_time date_time = watch_rtc_get_date_time();
+    state->current_year = date_time.unit.year + WATCH_RTC_REFERENCE_YEAR;
+    // reset the current page to 0, display days alive.
+    state->current_page = 0;
+
+    // fetch the user's birth date from the birthday register.
+    movement_birthdate_t movement_birthdate = (movement_birthdate_t) watch_get_backup_data(2);
+    state->birth_year = movement_birthdate.bit.year;
+    state->birth_month = movement_birthdate.bit.month;
+    state->birth_day = movement_birthdate.bit.day;
+}
+
+bool day_one_face_loop(movement_event_t event, movement_settings_t *settings, void *context) {
+    (void) settings;
+    day_one_state_t *state = (day_one_state_t *)context;
+
+    const uint8_t days_in_month[12] = {31, 29, 31, 30, 31, 30, 30, 31, 30, 31, 30, 31};
+    char buf[6];
+
+    switch (event.event_type) {
+        case EVENT_ACTIVATE:
+            _day_one_face_update(*state);
+            break;
+        case EVENT_LOW_ENERGY_UPDATE:
+        case EVENT_TICK:
+            if (state->current_page != 0) {
+                // if in settings mode, update whatever the current page is
+                switch (state->current_page) {
+                    case 1:
+                        watch_display_string("YR        ", 0);
+                        if (event.subsecond % 2) {
+                            sprintf(buf, "%4d", state->birth_year);
+                            watch_display_string(buf, 4);
+                        }
+                        break;
+                    case 2:
+                        watch_display_string("MO        ", 0);
+                        if (event.subsecond % 2) {
+                            sprintf(buf, "%2d", state->birth_month);
+                            watch_display_string(buf, 4);
+                        }
+                        break;
+                    case 3:
+                        watch_display_string("DA        ", 0);
+                        if (event.subsecond % 2) {
+                            sprintf(buf, "%2d", state->birth_day);
+                            watch_display_string(buf, 6);
+                        }
+                        break;
+                }
+            } else {
+                // otherwise, check if we have to update. the display only needs to change at midnight!
+                watch_date_time date_time = watch_rtc_get_date_time();
+                if (date_time.unit.hour == 0 &&  date_time.unit.minute == 0 && date_time.unit.second == 0) {
+                    _day_one_face_update(*state);
+                }
+            }
+            break;
+        case EVENT_MODE_BUTTON_UP:
+            movement_move_to_next_face();
+            break;
+        case EVENT_LIGHT_BUTTON_DOWN:
+            // only illuminate if we're in display mode
+            if (state->current_page == 0) movement_illuminate_led();
+            break;
+        case EVENT_LIGHT_BUTTON_UP:
+            // otherwise use the light button to advance settings pages.
+            if (state->current_page != 0) {
+                // go to next setting page...
+                state->current_page = (state->current_page + 1) % 4;
+                if (state->current_page == 0) {
+                    // ...unless we've been pushed back to display mode.
+                    movement_request_tick_frequency(1);
+                    // force display since it normally won't update til midnight.
+                    _day_one_face_update(*state);
+                }
+            }
+            break;
+        case EVENT_ALARM_BUTTON_UP:
+            // if we are on a settings page, increment whatever value we're setting.
+            if (state->current_page != 0) {
+                state->birthday_changed = true;
+                switch (state->current_page) {
+                    case 1:
+                        state->birth_year = state->birth_year + 1;
+                        if (state->birth_year > state->current_year) state->birth_year = 1900;
+                        break;
+                    case 2:
+                        state->birth_month = (state->birth_month % 12) + 1;
+                        break;
+                    case 3:
+                        state->birth_day = state->birth_day + 1;
+                        if (state->birth_day == 0 || state->birth_day > days_in_month[state->birth_month - 1]) {
+                            state->birth_day = 1;
+                        }
+                        break;
+                }
+            }
+            break;
+        case EVENT_ALARM_LONG_PRESS:
+            // if we aren't already in settings mode, put us there.
+            if (state->current_page == 0) {
+                state->current_page++;
+                movement_request_tick_frequency(4);
+            }
+            break;
+        case EVENT_TIMEOUT:
+            // return home if we're on a settings page (this saves our changes when we resign).
+            if (state->current_page != 0) {
+                movement_move_to_face(0);
+            }
+        default:
+            break;
+    }
+
+    return true;
+}
+
+void day_one_face_resign(movement_settings_t *settings, void *context) {
+    (void) settings;
+    day_one_state_t *state = (day_one_state_t *)context;
+
+    movement_request_tick_frequency(1);
+
+    // if the user changed their birth date, store it to the birth date register
+    if (state->birthday_changed) {
+        day_one_state_t *state = (day_one_state_t *)context;
+        movement_birthdate_t movement_birthdate = (movement_birthdate_t) watch_get_backup_data(2);
+        movement_birthdate.bit.year = state->birth_year;
+        movement_birthdate.bit.month = state->birth_month;
+        movement_birthdate.bit.day = state->birth_day;
+        watch_store_backup_data(movement_birthdate.reg, 2);
+        state->birthday_changed = false;
+    }
+}
diff --git a/movement/watch_faces/complications/day_one_face.h b/movement/watch_faces/complications/day_one_face.h
new file mode 100644
index 00000000..06c7816e
--- /dev/null
+++ b/movement/watch_faces/complications/day_one_face.h
@@ -0,0 +1,31 @@
+#ifndef DAY_ONE_FACE_H_
+#define DAY_ONE_FACE_H_
+
+#include "movement.h"
+
+// The Day One face is designed to count upwards from the wearer's date of birth. It also functions as an
+// interface for setting the birth date register, which other watch faces can use for various purposes.
+
+typedef struct {
+    uint8_t current_page;
+    uint16_t current_year;
+    uint16_t birth_year;
+    uint8_t birth_month;
+    uint8_t birth_day;
+    bool birthday_changed;
+} day_one_state_t;
+
+void day_one_face_setup(movement_settings_t *settings, void ** context_ptr);
+void day_one_face_activate(movement_settings_t *settings, void *context);
+bool day_one_face_loop(movement_event_t event, movement_settings_t *settings, void *context);
+void day_one_face_resign(movement_settings_t *settings, void *context);
+
+static const watch_face_t day_one_face = {
+    day_one_face_setup,
+    day_one_face_activate,
+    day_one_face_loop,
+    day_one_face_resign,
+    NULL
+};
+
+#endif // DAY_ONE_FACE_H_
diff --git a/movement/watch_faces/complications/stopwatch_face.c b/movement/watch_faces/complications/stopwatch_face.c
new file mode 100644
index 00000000..d1d1ee73
--- /dev/null
+++ b/movement/watch_faces/complications/stopwatch_face.c
@@ -0,0 +1,76 @@
+#include <stdlib.h>
+#include <string.h>
+#include "stopwatch_face.h"
+#include "watch.h"
+
+void stopwatch_face_setup(movement_settings_t *settings, void ** context_ptr) {
+    (void) settings;
+    if (*context_ptr == NULL) *context_ptr = malloc(sizeof(stopwatch_state_t));
+}
+
+void stopwatch_face_activate(movement_settings_t *settings, void *context) {
+    (void) settings;
+    memset(context, 0, sizeof(stopwatch_state_t));
+}
+
+bool stopwatch_face_loop(movement_event_t event, movement_settings_t *settings, void *context) {
+    (void) settings;
+
+    stopwatch_state_t *stopwatch_state = (stopwatch_state_t *)context;
+    char buf[14];
+
+    switch (event.event_type) {
+        case EVENT_ACTIVATE:
+            watch_set_colon();
+            stopwatch_state->running = false;
+            watch_display_string("st 00000", 0);
+            break;
+        case EVENT_TICK:
+            if (stopwatch_state->running) {
+                stopwatch_state->seconds++;
+                if (stopwatch_state->seconds == 60) {
+                    stopwatch_state->minutes++;
+                    stopwatch_state->seconds = 0;
+                }
+                if (stopwatch_state->minutes == 60) {
+                    stopwatch_state->hours++;
+                    stopwatch_state->minutes = 0;
+                }
+            }
+
+            sprintf(buf, "st%2d%02d%02d", stopwatch_state->hours, stopwatch_state->minutes, stopwatch_state->seconds);
+            watch_display_string(buf, 0);
+            break;
+        case EVENT_MODE_BUTTON_UP:
+            movement_move_to_next_face();
+            break;
+        case EVENT_LIGHT_BUTTON_DOWN:
+            movement_illuminate_led();
+            if (!stopwatch_state->running) {
+                stopwatch_state->seconds = 0;
+                stopwatch_state->minutes = 0;
+                stopwatch_state->hours = 0;
+                watch_display_string("st 00000", 0);
+            }
+            break;
+        case EVENT_ALARM_BUTTON_DOWN:
+            stopwatch_state->running = !stopwatch_state->running;
+            break;
+        case EVENT_TIMEOUT:
+            // explicitly ignore the timeout event so we stay on screen
+            break;
+        case EVENT_LOW_ENERGY_UPDATE:
+            stopwatch_state->running = false;
+            watch_set_indicator(WATCH_INDICATOR_BELL);
+            break;
+        default:
+            break;
+    }
+
+    return true;
+}
+
+void stopwatch_face_resign(movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+}
\ No newline at end of file
diff --git a/movement/watch_faces/complications/stopwatch_face.h b/movement/watch_faces/complications/stopwatch_face.h
new file mode 100644
index 00000000..537c01ce
--- /dev/null
+++ b/movement/watch_faces/complications/stopwatch_face.h
@@ -0,0 +1,26 @@
+#ifndef STOPWATCH_FACE_H_
+#define STOPWATCH_FACE_H_
+
+#include "movement.h"
+
+typedef struct {
+    bool running;
+    uint8_t seconds;
+    uint8_t minutes;
+    uint8_t hours;
+} stopwatch_state_t;
+
+void stopwatch_face_setup(movement_settings_t *settings, void ** context_ptr);
+void stopwatch_face_activate(movement_settings_t *settings, void *context);
+bool stopwatch_face_loop(movement_event_t event, movement_settings_t *settings, void *context);
+void stopwatch_face_resign(movement_settings_t *settings, void *context);
+
+static const watch_face_t stopwatch_face = {
+    stopwatch_face_setup,
+    stopwatch_face_activate,
+    stopwatch_face_loop,
+    stopwatch_face_resign,
+    NULL
+};
+
+#endif // STOPWATCH_FACE_H_
\ No newline at end of file
diff --git a/movement/watch_faces/demos/voltage_face.c b/movement/watch_faces/demos/voltage_face.c
new file mode 100644
index 00000000..98b22c76
--- /dev/null
+++ b/movement/watch_faces/demos/voltage_face.c
@@ -0,0 +1,66 @@
+#include <stdlib.h>
+#include <string.h>
+#include "voltage_face.h"
+#include "watch.h"
+
+void _voltage_face_update_display() {
+    char buf[14];
+    float voltage = (float)watch_get_vcc_voltage() / 1000.0;
+    sprintf(buf, "BA  %4.2f V", voltage);
+    // printf("%s\n", buf);
+    watch_display_string(buf, 0);
+}
+
+void voltage_face_setup(movement_settings_t *settings, void ** context_ptr) {
+    (void) settings;
+    (void) context_ptr;
+}
+
+void voltage_face_activate(movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+    watch_enable_adc();
+    // if we set the reference voltage here, watch_get_vcc_voltage won't do it over and over
+    watch_set_analog_reference_voltage(ADC_REFERENCE_INTREF);
+}
+
+bool voltage_face_loop(movement_event_t event, movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+    watch_date_time date_time;
+    switch (event.event_type) {
+        case EVENT_MODE_BUTTON_UP:
+            movement_move_to_next_face();
+            break;
+        case EVENT_LIGHT_BUTTON_DOWN:
+            movement_illuminate_led();
+            break;
+        case EVENT_ACTIVATE:
+            _voltage_face_update_display();
+            break;
+        case EVENT_TICK:
+            date_time = watch_rtc_get_date_time();
+            if (date_time.unit.second % 5 == 4) {
+                watch_set_indicator(WATCH_INDICATOR_SIGNAL);
+            } else if (date_time.unit.second % 5 == 0) {
+                _voltage_face_update_display();
+                watch_clear_indicator(WATCH_INDICATOR_SIGNAL);
+            }
+            break;
+        case EVENT_TIMEOUT:
+            movement_move_to_face(0);
+            break;
+        default:
+            break;
+    }
+
+    return true;
+}
+
+void voltage_face_resign(movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+    // make sure to restore the default in the end.
+    watch_set_analog_reference_voltage(ADC_REFCTRL_REFSEL_INTVCC2_Val);
+    watch_disable_adc();
+}
diff --git a/movement/watch_faces/demos/voltage_face.h b/movement/watch_faces/demos/voltage_face.h
new file mode 100644
index 00000000..da580da5
--- /dev/null
+++ b/movement/watch_faces/demos/voltage_face.h
@@ -0,0 +1,19 @@
+#ifndef VOLTAGE_FACE_H_
+#define VOLTAGE_FACE_H_
+
+#include "movement.h"
+
+void voltage_face_setup(movement_settings_t *settings, void ** context_ptr);
+void voltage_face_activate(movement_settings_t *settings, void *context);
+bool voltage_face_loop(movement_event_t event, movement_settings_t *settings, void *context);
+void voltage_face_resign(movement_settings_t *settings, void *context);
+
+static const watch_face_t voltage_face = {
+    voltage_face_setup,
+    voltage_face_activate,
+    voltage_face_loop,
+    voltage_face_resign,
+    NULL
+};
+
+#endif // VOLTAGE_FACE_H_
\ No newline at end of file