#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);
+#include "watch_utility.h"
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);
+ // Enable analog circuitry on the sense pin, which is tied to the thermistor resistor divider.
+ watch_enable_analog_input(THERMISTOR_SENSE_PIN);
+ // Enable digital output on the enable pin, which is the power to the thermistor circuit.
+ watch_enable_digital_output(THERMISTOR_ENABLE_PIN);
+ // and make sure it's off.
+ watch_set_pin_level(THERMISTOR_ENABLE_PIN, !THERMISTOR_ENABLE_VALUE);
}
void thermistor_driver_disable() {
- // Enable the ADC peripheral, which we'll use to read the thermistor value.
+ // Disable the ADC peripheral.
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);
+ // Disable analog circuitry on the sense pin to save power.
+ watch_disable_analog_input(THERMISTOR_SENSE_PIN);
+ // Disable the enable pin's output circuitry.
+ watch_disable_digital_output(THERMISTOR_ENABLE_PIN);
}
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];
+ // set the enable pin to the level that powers the thermistor circuit.
+ watch_set_pin_level(THERMISTOR_ENABLE_PIN, THERMISTOR_ENABLE_VALUE);
+ // get the sense pin level
+ uint16_t value = watch_get_analog_pin_level(THERMISTOR_SENSE_PIN);
+ // and then set the enable pin to the opposite value to power down the thermistor circuit.
+ watch_set_pin_level(THERMISTOR_ENABLE_PIN, !THERMISTOR_ENABLE_VALUE);
+
+ return watch_utility_thermistor_temperature(value, THERMISTOR_HIGH_SIDE, THERMISTOR_B_COEFFICIENT, THERMISTOR_NOMINAL_TEMPERATURE, THERMISTOR_NOMINAL_RESISTANCE, THERMISTOR_SERIES_RESISTANCE);
}
-
-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;
-}
-
#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.
+// TODO: Do these belong in movement_config.h? In settings we can set on the watch? In an EEPROM configuration area?
+// Think on this. [joey 11/22]
+#define THERMISTOR_SENSE_PIN (A2)
+#define THERMISTOR_ENABLE_PIN (A0)
+#define THERMISTOR_ENABLE_VALUE (false)
+#define THERMISTOR_HIGH_SIDE (true)
+#define THERMISTOR_B_COEFFICIENT (3380.0)
+#define THERMISTOR_NOMINAL_TEMPERATURE (25.0)
+#define THERMISTOR_NOMINAL_RESISTANCE (10000.0)
+#define THERMISTOR_SERIES_RESISTANCE (10000.0)
void thermistor_driver_enable();
void thermistor_driver_disable();
*/
const char * watch_utility_get_weekday(watch_date_time date_time);
+/** @brief Returns a temperature in degrees Celsius for a given thermistor voltage divider circuit.
+ * @param value The raw analog reading from the thermistor pin (0-65535)
+ * @param highside True if the thermistor is connected to VCC and the series resistor is connected
+ * to GND; false if the thermistor is connected to GND and the series resistor is
+ * connected to VCC.
+ * @param b_coefficient From your thermistor's data sheet, the B25/85 coefficient. A typical value
+ * will be between 2000 and 5000.
+ * @param nominal_temperature From your thermistor's data sheet, the temperature (in Celsius) at
+ * which the thermistor's resistance is at its nominal value.
+ * @param nominal_resistance The thermistor's resistance at the nominal temperature.
+ * @param series_resistance The value of the other resistor in the voltage divider.
+ * @note Ported from Adafruit's MIT-licensed CircuitPython thermistor code, (c) 2017 Scott Shawcroft:
+ * https://github.com/adafruit/Adafruit_CircuitPython_Thermistor/blob/main/adafruit_thermistor.py
+ */
+float watch_utility_thermistor_temperature(uint16_t value, bool highside, float b_coefficient, float nominal_temperature, float nominal_resistance, float series_resistance);
+
#endif
projects / sensor-watch.git / commitdiff