movement: add thermistor readout face

movement/watch_faces/thermistor/thermistor_driver.c

@@ -0,0 +1,76 @@
+#include "thermistor_driver.h"
+#include "watch.h"
+
+#define THERMISTOR_B_COEFFICIENT (3950.0)
+#define THERMISTOR_NOMINAL_TEMPERATURE (25.0)
+#define THERMISTOR_NOMINAL_RESISTANCE (10000.0)
+#define THERMISTOR_SERIES_RESISTANCE (10000.0)
+
+// TODO: we really need a math library.
+uint32_t msb(uint32_t v);
+double ln(double y);
+
+void thermistor_driver_enable() {
+    // Enable the ADC peripheral, which we'll use to read the thermistor value.
+    watch_enable_adc();
+    // Enable analog circuitry on pin A1, which is tied to the thermistor resistor divider.
+    watch_enable_analog_input(A1);
+    // Enable digital output on A0, which is the power to the thermistor circuit.
+    watch_enable_digital_output(A0);
+}
+
+void thermistor_driver_disable() {
+    // Enable the ADC peripheral, which we'll use to read the thermistor value.
+    watch_disable_adc();
+    // Disable analog circuitry on pin A1 to save power.
+    watch_disable_analog_input(A1);
+    // Disable A0's output circuitry.
+    watch_disable_digital_output(A0);
+}
+
+float thermistor_driver_get_temperature() {
+    // set A0 high to power the thermistor circuit.
+    watch_set_pin_level(A0, true);
+    // get the pin level
+    uint16_t val = watch_get_analog_pin_level(A1);
+    // and then set A0 low to power down the thermistor circuit.
+    watch_set_pin_level(A0, false);
+
+    double reading = (double)val;
+    reading = (1023.0 * THERMISTOR_SERIES_RESISTANCE) / (reading / 64.0);
+    reading -= THERMISTOR_SERIES_RESISTANCE;
+    reading = reading / THERMISTOR_NOMINAL_RESISTANCE;
+    reading = ln(reading);
+    reading /= THERMISTOR_B_COEFFICIENT;
+    reading += 1.0 / (THERMISTOR_NOMINAL_TEMPERATURE + 273.15);
+    reading = 1.0 / reading;
+    reading -= 273.15;
+
+    return reading;
+}
+
+uint32_t msb(uint32_t v) {
+  static const int pos[32] = {0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9};
+  v |= v >> 1;
+  v |= v >> 2;
+  v |= v >> 4;
+  v |= v >> 8;
+  v |= v >> 16;
+  v = (v >> 1) + 1;
+  return pos[(v * 0x077CB531UL) >> 27];
+}
+
+double ln(double y) {
+    int log2;
+    double divisor, x, result;
+
+    log2 = msb((int)y); // See: https://stackoverflow.com/a/4970859/6630230
+    divisor = (double)(1 << log2);
+    x = y / divisor;    // normalized value between [1.0, 2.0]
+
+    result = -1.7417939 + (2.8212026 + (-1.4699568 + (0.44717955 - 0.056570851 * x) * x) * x) * x;
+    result += ((double)log2) * 0.69314718; // ln(2) = 0.69314718
+
+    return result;
+}
+

movement/watch_faces/thermistor/thermistor_driver.h

@@ -0,0 +1,13 @@
+#ifndef THERMISTOR_DRIVER_H_
+#define THERMISTOR_DRIVER_H_
+
+// NOTE: This implementation is specific to one prototype sensor board, OSO-MISC-21-009, but both
+// the sensor board design and this implementation are likely to change. Thermistor functionality
+// may even end up being baked into the Sensor Watch library. This is all by way of saying this
+// code is very temporary and the thermistor screens will likely get a rewrite in the future.
+
+void thermistor_driver_enable();
+void thermistor_driver_disable();
+float thermistor_driver_get_temperature();
+
+#endif // THERMISTOR_DRIVER_H_

movement/watch_faces/thermistor/thermistor_readout_face.c

@@ -0,0 +1,73 @@
+#include <stdlib.h>
+#include <string.h>
+#include "thermistor_readout_face.h"
+#include "thermistor_driver.h"
+#include "watch.h"
+
+void _thermistor_readout_face_update_display(bool in_fahrenheit) {
+    float temperature_c = thermistor_driver_get_temperature();
+    char buf[14];
+    if (in_fahrenheit) {
+        sprintf(buf, "%4.1f#F", temperature_c * 1.8 + 32.0);
+    } else {
+        sprintf(buf, "%4.1f#C", temperature_c);
+    }
+    watch_display_string(buf, 4);
+}
+
+void thermistor_readout_face_setup(movement_settings_t *settings, void ** context_ptr) {
+    (void) settings;
+    (void) context_ptr;
+}
+
+void thermistor_readout_face_activate(movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+    watch_display_string("TE", 0);
+    thermistor_driver_enable();
+}
+
+bool thermistor_readout_face_loop(movement_event_t event, movement_settings_t *settings, void *context) {
+    (void) context;
+    watch_date_time date_time = watch_rtc_get_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_ALARM_BUTTON_UP:
+            settings->bit.use_imperial_units = !settings->bit.use_imperial_units;
+            _thermistor_readout_face_update_display(settings->bit.use_imperial_units);
+            break;
+        case EVENT_ACTIVATE:
+            // force a measurement to be taken immediately.
+            date_time.unit.second = 0;
+            // fall through
+        case EVENT_TICK:
+            if (date_time.unit.second % 5 == 4) {
+                // Not 100% on this, but I like the idea of using the signal indicator to indicate that we're sensing data.
+                // In this case we turn the indicator on a second before the reading is taken, and clear it when we're done.
+                // In reality the measurement takes a fraction of a second, but this is just to show something is happening.
+                watch_set_indicator(WATCH_INDICATOR_SIGNAL);
+            } else if (date_time.unit.second % 5 == 0) {
+                _thermistor_readout_face_update_display(settings->bit.use_imperial_units);
+                watch_clear_indicator(WATCH_INDICATOR_SIGNAL);
+            }
+            break;
+        case EVENT_TIMEOUT:
+            movement_move_to_face(0);
+            break;
+        default:
+            break;
+    }
+
+    return true;
+}
+
+void thermistor_readout_face_resign(movement_settings_t *settings, void *context) {
+    (void) settings;
+    (void) context;
+    thermistor_driver_disable();
+}

movement/watch_faces/thermistor/thermistor_readout_face.h

@@ -0,0 +1,19 @@
+#ifndef THERMISTOR_FACE_H_
+#define THERMISTOR_FACE_H_
+
+#include "movement.h"
+
+void thermistor_readout_face_setup(movement_settings_t *settings, void ** context_ptr);
+void thermistor_readout_face_activate(movement_settings_t *settings, void *context);
+bool thermistor_readout_face_loop(movement_event_t event, movement_settings_t *settings, void *context);
+void thermistor_readout_face_resign(movement_settings_t *settings, void *context);
+
+static const watch_face_t thermistor_readout_face = {
+    thermistor_readout_face_setup,
+    thermistor_readout_face_activate,
+    thermistor_readout_face_loop,
+    thermistor_readout_face_resign,
+    NULL
+};
+
+#endif // THERMISTOR_FACE_H_