From: Jan "Yenya" Kasprzak <kas@fi.muni.cz>
Date: Wed, 6 Mar 2013 23:19:43 +0000 (+0100)
Subject: battery.c: adjustment for 1.1V internal reference
X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?p=bike-lights.git;a=commitdiff_plain;h=60d17ce8b779c966e6285f1fb9f3de3118752092

battery.c: adjustment for 1.1V internal reference
---

diff --git a/firmware/battery.c b/firmware/battery.c
index d7123e9..192acf0 100644
--- a/firmware/battery.c
+++ b/firmware/battery.c
@@ -5,6 +5,12 @@
 #define BATTERY_ADC_SHIFT	6
 #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;
 volatile unsigned char battery_critical;
@@ -46,7 +52,7 @@ unsigned char battery_100mv()
 /* convert value in mV to value of ADC shifted by BATTERY_ADC_SHIFT */
 #define MV_TO_ADC(x) \
 	((uint16_t)(((uint32_t)(x) * 1024 * (1 << BATTERY_ADC_SHIFT)) \
-		/ ((uint32_t) 1100 \
+		/ ((uint32_t) AREF_1100MV \
 			* ((RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO))))
 
 /* convert value in mV to upper 8 bits of ADC value << BATTERY_ADC_SHIFT */