X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?p=bike-lights.git;a=blobdiff_plain;f=firmware%2Fbattery.c;fp=firmware%2Fbattery.c;h=472c1c47f099093c59bfe6454983276687e9dad8;hp=0000000000000000000000000000000000000000;hb=3aa04c7f0ae362c4494d272ecf249d862e3aec01;hpb=5b2ef9def765f5bfde371bff0f811c9d9cc8d682

diff --git a/firmware/battery.c b/firmware/battery.c
new file mode 100644
index 0000000..472c1c4
--- /dev/null
+++ b/firmware/battery.c
@@ -0,0 +1,25 @@
+#include <avr/io.h>
+
+#include "lights.h"
+
+#define RESISTOR_HI	1500	// kOhm
+#define RESISTOR_LO	 150	// kOhm
+
+volatile unsigned char battery_100mv;
+
+void battery_adc(uint16_t adcval)
+{
+	/*
+	 * This is tricky: we need to maintain precision, so we first
+	 * multiply adcval by as big number as possible to fit uint16_t,
+	 * then divide to get the final value,
+	 * and finally type-cast it to unsigned char.
+	 * We don't do running average, as the required precision
+	 * is coarse (0.1 V).
+	 */
+	battery_100mv = (unsigned char)
+		((adcval * 11                              // 1.1V
+		* (RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO    // resistor ratio
+		/ 4) >> 8);                                // divide by 1024
+}
+