diff options
| -rw-r--r-- | movement/watch_faces/thermistor/thermistor_driver.c | 82 | ||||
| -rw-r--r-- | movement/watch_faces/thermistor/thermistor_driver.h | 14 | ||||
| -rw-r--r-- | watch-library/watch/watch_utility.c | 21 | ||||
| -rw-r--r-- | watch-library/watch/watch_utility.h | 16 |
4 files changed, 67 insertions, 66 deletions
diff --git a/movement/watch_faces/thermistor/thermistor_driver.c b/movement/watch_faces/thermistor/thermistor_driver.c index 9e5d6fd7..37b5ba3f 100644 --- a/movement/watch_faces/thermistor/thermistor_driver.c +++ b/movement/watch_faces/thermistor/thermistor_driver.c @@ -1,76 +1,34 @@ #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; -} - diff --git a/movement/watch_faces/thermistor/thermistor_driver.h b/movement/watch_faces/thermistor/thermistor_driver.h index 837eb15b..a0b197de 100644 --- a/movement/watch_faces/thermistor/thermistor_driver.h +++ b/movement/watch_faces/thermistor/thermistor_driver.h @@ -1,10 +1,16 @@ #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(); diff --git a/watch-library/watch/watch_utility.c b/watch-library/watch/watch_utility.c index a0f361b4..bfa3073a 100644 --- a/watch-library/watch/watch_utility.c +++ b/watch-library/watch/watch_utility.c @@ -22,6 +22,7 @@ * SOFTWARE. */ +#include <math.h> #include "watch_utility.h" const char * watch_utility_get_weekday(watch_date_time date_time) { @@ -33,3 +34,23 @@ const char * watch_utility_get_weekday(watch_date_time date_time) { } return weekdays[(date_time.unit.day + 13 * (date_time.unit.month + 1) / 5 + date_time.unit.year + date_time.unit.year / 4 + 525) % 7]; } + +float watch_utility_thermistor_temperature(uint16_t value, bool highside, float b_coefficient, float nominal_temperature, float nominal_resistance, float series_resistance) { + float reading = (float)value; + + if (highside) { + reading = (1023.0 * series_resistance) / (reading / 64.0); + reading -= series_resistance; + } else { + reading = series_resistance / (65535.0 / value - 1.0); + } + + reading = reading / nominal_resistance; + reading = log(reading); + reading /= b_coefficient; + reading += 1.0 / (nominal_temperature + 273.15); + reading = 1.0 / reading; + reading -= 273.15; + + return reading; +} diff --git a/watch-library/watch/watch_utility.h b/watch-library/watch/watch_utility.h index e8808923..aada783f 100644 --- a/watch-library/watch/watch_utility.h +++ b/watch-library/watch/watch_utility.h @@ -38,4 +38,20 @@ */ 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 |