Switch to using internal cc1111 temperature sensor

[fw/altos] / src / ao_convert.c

diff --git a/src/ao_convert.c b/src/ao_convert.c
index 57ed73701abefe29d99d888ddbe35b4a586b982a..f29ce9e975d35256de23db57cd9de5f89a8d39e5 100644 (file)
--- a/src/ao_convert.c
+++ b/src/ao_convert.c
@@ -49,7 +49,15 @@ ao_temp_to_dC(int16_t temp) __reentrant
        int16_t ret;
 
        ao_mutex_get(&ao_temp_mutex);
-       ret = (int16_t) ((temp >> 4) * 3300L / 2047L) - 500;
+       /* Output voltage at 0°C = 0.755V
+        * Coefficient = 0.00247V/°C
+        * Reference voltage = 1.25V
+        *
+        * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
+        *      = (value - 19791.268) / 32768 * 1.25 / 0.00247
+        *      ≃ (value - 19791) * 1012 / 65536
+        */
+       ret = ((temp - 19791) * 1012L) >> 16;
        ao_mutex_put(&ao_temp_mutex);
        return ret;
 }