summaryrefslogtreecommitdiffstats
path: root/watch-library/watch
diff options
context:
space:
mode:
authorJoey Castillo <jose.castillo@gmail.com>2021-11-22 17:31:51 -0500
committerJoey Castillo <jose.castillo@gmail.com>2021-11-22 17:31:51 -0500
commit0ca729eaba7cdca543bc563912095df98f2b3786 (patch)
tree9b8f74e4fb698bcc3bf70f5b6cfb84fb8f9b604c /watch-library/watch
parentfb8f4584a59b1f1ffc804a7aa8311e91c1629f94 (diff)
downloadSensor-Watch-0ca729eaba7cdca543bc563912095df98f2b3786.tar.gz
Sensor-Watch-0ca729eaba7cdca543bc563912095df98f2b3786.tar.bz2
Sensor-Watch-0ca729eaba7cdca543bc563912095df98f2b3786.zip
move thermistor calculation to watch utilities
Diffstat (limited to 'watch-library/watch')
-rw-r--r--watch-library/watch/watch_utility.c21
-rw-r--r--watch-library/watch/watch_utility.h16
2 files changed, 37 insertions, 0 deletions
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