From b980e6b76d07341c02b03aae3966df106ec71b29 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Fri, 31 Jan 2014 13:42:47 +0100
Subject: [PATCH] Battery voltage measurement and reporting

TODO: calculate the power output based on this
---
 firmware/main.c | 69 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 63 insertions(+), 6 deletions(-)

diff --git a/firmware/main.c b/firmware/main.c
index ddbd2d3..edbbf0a 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -66,8 +66,26 @@ static unsigned char intensity = 0; // selected power level
 
 /* which state (output on or output off) are we measuring now */
 static volatile unsigned char adc_type, adc_drop;
+#define ADC_RUNAVG_SHIFT 5	// running average shift on batt_on, batt_off
 static volatile uint16_t batt_on, batt_off; // measured voltage
 
+/*
+ * The voltage divider has 1M5 and 300K resistors (i.e. it measures 1/6th of
+ * the real voltage), ADC uses 1.1V internal reference.
+ * Macro to calculate upper eight bits of the ADC running-averaged value
+ * from the voltage in milivolts.
+ */
+#define ADC_1100MV_VALUE	1071	// measured, not exactly 1100
+#define MV_TO_ADC8(mV)	((unsigned char)(((uint32_t)(1UL << ADC_RUNAVG_SHIFT) \
+				* (1024UL * (mV)) \
+				/ (6UL * ADC_1100MV_VALUE)) >> 8))
+#define BATT_N_LEVELS 	3
+static unsigned char batt_levels[BATT_N_LEVELS] = {
+	MV_TO_ADC8(3500),
+	MV_TO_ADC8(3700),
+	MV_TO_ADC8(3900),
+};
+
 /* timing by WDT */
 static volatile unsigned char jiffies, next_clock_tick;
 
@@ -112,15 +130,15 @@ ISR(ADC_vect)
 	// so don't bother with it.
 	if (adc_type == 0) {
 		if (batt_off) {
-			batt_off += adcw - (batt_off >> 5);
+			batt_off += adcw - (batt_off >> ADC_RUNAVG_SHIFT);
 		} else {
-			batt_off = adcw << 5;
+			batt_off = adcw << ADC_RUNAVG_SHIFT;
 		}
 	} else {
 		if (batt_on) {
-			batt_on += adcw - (batt_on >> 5);
+			batt_on += adcw - (batt_on >> ADC_RUNAVG_SHIFT);
 		} else {
-			batt_on = adcw << 5;
+			batt_on = adcw << ADC_RUNAVG_SHIFT;
 		}
 	}
 }
@@ -136,7 +154,8 @@ static void pwm_init()
 	TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
 	GTCCR = _BV(COM1B1) | _BV(PWM1B);
 	OCR1C = 255;
-	OCR1B = steps[0];
+	// OCR1B = steps[0];
+	OCR1B = 0;
 	TIMSK = _BV(OCIE1B) | _BV(TOIE1);
 }
 
@@ -349,10 +368,27 @@ static void timer_check_buttons()
 static unsigned char blink_on_time, blink_off_time, n_blinks;
 static unsigned char blink_counter;
 
+static unsigned char battery_level()
+{
+	unsigned char i, adc8;
+
+	// NOTE: we use 8-bit value only, so we don't need lock to protect
+	// us against concurrently running ADC IRQ handler:
+	adc8 = batt_off >> 8;
+
+	for (i = 0; i < BATT_N_LEVELS; i++)
+		if (batt_levels[i] > adc8)
+			break;
+
+	return i;
+}
+
 static void status_led_next_pattern()
 {
+
 	// for now, display the selected intensity
-	n_blinks = intensity + 1;
+	// n_blinks = intensity + 1;
+	n_blinks = battery_level() + 1;
 	blink_on_time = 0;
 	blink_off_time = 2;
 	blink_counter = 10;
@@ -378,6 +414,13 @@ int main()
 {
 	log_init();
 
+#if 0
+	log_word(batt_levels[0]);
+	log_word(batt_levels[1]);
+	log_word(batt_levels[2]);
+	log_flush();
+#endif
+
 	power_down();
 
 	sei();
@@ -397,6 +440,20 @@ int main()
 			next_clock_tick = 0;
 			timer_check_buttons();
 			timer_blink();
+			if ((jiffies & 0x0F) == 0) {
+				unsigned char i;
+
+				for (i = 0; i < BATT_N_LEVELS; i++)
+					if (batt_levels[i] > batt_off)
+						break;
+
+#if 0
+				log_byte(0xcc);
+				log_byte(i);
+				log_byte(batt_off >> 8);
+				log_byte(batt_on >> 8);
+#endif
+			}
 			log_flush();
 		}
 	}
-- 
2.43.5