From 3aa04c7f0ae362c4494d272ecf249d862e3aec01 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Mon, 12 Nov 2012 23:47:06 +0100
Subject: [PATCH] battery voltage sensor

---
 firmware/Makefile  |  2 +-
 firmware/adc.c     |  3 ++-
 firmware/battery.c | 25 +++++++++++++++++++++++++
 firmware/lights.h  |  4 ++++
 4 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 firmware/battery.c

diff --git a/firmware/Makefile b/firmware/Makefile
index 6f2a946..70c2c32 100644
--- a/firmware/Makefile
+++ b/firmware/Makefile
@@ -1,7 +1,7 @@
 
 PROGRAM=lights
 SRC=main.c logging.c adc.c pwm.c tmr.c pwmled.c gpio.c ambient.c pattern.c \
-	buttons.c
+	buttons.c battery.c
 OBJ=$(SRC:.c=.o)
 
 
diff --git a/firmware/adc.c b/firmware/adc.c
index 3fdbe32..8ec62e2 100644
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -99,7 +99,8 @@ ISR(ADC_vect) { // IRQ handler
 		pwmled_adc(current_adc, adcval);
 	if (current_adc == AMBIENT_ADC)
 		ambient_adc(adcval);
-	// TODO battery sense, etc.
+	if (current_adc == BATTERY_ADC)
+		battery_adc(adcval);
 	
 	start_next_adc();
 }
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
+}
+
diff --git a/firmware/lights.h b/firmware/lights.h
index c866349..243700f 100644
--- a/firmware/lights.h
+++ b/firmware/lights.h
@@ -65,6 +65,10 @@ void led_set_status(unsigned char status);
 void init_buttons();
 void timer_check_buttons();
 
+/* battery.c */
+extern volatile unsigned char battery_100mv;
+void battery_adc();
+
 /* main.c */
 void hw_setup();
 void hw_suspend();
-- 
2.39.3