X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?p=tinyboard.git;a=blobdiff_plain;f=projects%2Fstep-up%2Fbattery.c;fp=projects%2Fstep-up%2Fbattery.c;h=ceb53cb2c1133eecb104b607fd79d67f15cfbbee;hp=0000000000000000000000000000000000000000;hb=287f589eb6aee0d3aa9726106c6782c41c81ec6a;hpb=887aa3ba899b44aa07cfabfab4ce3495074f0788

diff --git a/projects/step-up/battery.c b/projects/step-up/battery.c
new file mode 100644
index 0000000..ceb53cb
--- /dev/null
+++ b/projects/step-up/battery.c
@@ -0,0 +1,89 @@
+#include <avr/io.h>
+
+#include "lights.h"
+
+#define BATTERY_ADC_SHIFT	2
+#define RESISTOR_HI	1500	// kOhm
+#define RESISTOR_LO	 100	// kOhm
+/*
+ * The internal 1.1V reference has tolerance from 1.0 to 1.2V
+ * (datasheet, section 19.6). We have to measure the actual value
+ * of our part.
+ */
+#define AREF_1100MV	1060	// mV
+
+static volatile uint16_t battery_adcval;
+static unsigned char initial_readings = 0;
+
+void init_battery()
+{
+	battery_adcval = 0;
+	initial_readings = 5;
+}
+
+unsigned char battery_100mv()
+{
+	/*
+	 * 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).
+	 */
+	return (unsigned char)
+		((uint16_t)(
+		(battery_adcval >> BATTERY_ADC_SHIFT)
+		* (11                                      // 1.1V
+		* (RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO    // resistor ratio
+		/ 4)) >> 8);                               // divide by 1024
+}
+
+void battery_adc(uint16_t adcval)
+{
+	if (initial_readings) {
+		initial_readings--;
+		battery_adcval = adcval << BATTERY_ADC_SHIFT;
+	} else if (battery_adcval == 0) {
+		battery_adcval = adcval << BATTERY_ADC_SHIFT;
+	} else { // running average
+		battery_adcval += (adcval
+			- (battery_adcval >> BATTERY_ADC_SHIFT));
+	}
+#if 0
+	log_byte(battery_100mv());
+	log_flush();
+#endif
+}
+
+unsigned char battery_gauge()
+{
+	unsigned char b8 = battery_100mv();
+	unsigned char rv;
+
+	if        (b8 < 70) {
+		rv = 1;
+	} else if (b8 < 75) {
+		rv = 2;
+	} else if (b8 < 80) {
+		rv = 3;
+	} else if (b8 < 85) {
+		rv = 4;
+	} else if (b8 < 90) {
+		rv = 5;
+	} else if (b8 < 95) {
+		rv = 6;
+	} else {
+		rv = 7;
+	}
+
+	if (rv == 1 && !initial_readings)
+		set_error(ERR_BATTERY);
+
+#if 0
+	log_byte(0xbb);
+	log_byte(rv);
+	log_flush();
+#endif
+	return rv;
+}