Monitor battery level using the ADC

1 files changed, 46 insertions, 4 deletions

diff --git a/main.c b/main.c
index beeb87a..9efbffa 100644
--- a/main.c
+++ b/main.c
@@ -1,4 +1,5 @@
 #include <stdint.h>
+#include <stdlib.h>
 #include <avr/wdt.h>
 #include <avr/sleep.h>
 #include <avr/interrupt.h>
@@ -7,6 +8,8 @@
 #include "fpm.h"
 #include "uart.h"
 
+#define BATMIN             5100
+
 #define SERVO_PIN          PB1
 #define SERVO_DDR          DDRB
 
@@ -19,6 +22,7 @@
 #define LED_DDR            DDRB
 #define LED_PORT           PORTB
 
+#define PWR_BATCHK         PB2
 #define PWR_SERVO          PB3
 #define PWR_FPM            PB4
 #define PWR_DDR            DDRB
@@ -100,19 +104,57 @@ static inline void flash_led(void)
 	}
 }
 
+static inline void pwron_batchk(void)
+{
+	PWR_PORT &= ~(1 << PWR_BATCHK);
+}
+
+static inline void pwroff_batchk(void)
+{
+	PWR_PORT |= (1 << PWR_BATCHK);
+}
+
+static void check_bat(void)
+{
+	uint16_t vbg, vcc;
+
+	pwron_batchk();
+
+	ADMUX |= (1 << REFS1) | (1 << REFS0);
+	ADCSRA |= (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1); /* clk: 50-200 kHz */
+
+	_delay_us(500); /* https://www.sciencetronics.com/greenphotons/?p=1521 */
+
+	ADCSRA |= (1 << ADSC);
+	while (ADCSRA & (1 << ADSC))
+		; 
+
+	ADCSRA &= ~(1 << ADEN);
+	vbg = (1100UL * ADC) / 1024;
+	ADCSRA &= ~(1 << ADEN);
+	
+	pwroff_batchk();
+
+	vcc = (vbg * 66) / 10; /* 56k/10k divider */
+	if (vcc < BATMIN)
+		flash_led();
+}
+
 int main(void)
 {
 	uint16_t id;
 
-	/* disable watchdog timer */
+	/* disable wdt */
 	cli();
 	wdt_reset();
 	MCUSR &= ~(1 << WDRF);
 	WDTCSR |= (1 << WDCE) | (1 << WDE);
 	WDTCSR = 0x00;
 
+	PWR_DDR |= (1 << PWR_BATCHK) | (1 << PWR_FPM) | (1 << PWR_SERVO);
+	pwroff_batchk();
+
 	uart_init();
-	PWR_DDR |= (1 << PWR_FPM) | (1 << PWR_SERVO);
 	pwron_fpm();
 	fpm_init();
 
@@ -144,9 +186,9 @@ int main(void)
 	PCMSK2 |= ((1 << FRONT_LOCK_INT) | (1 << ENROLL_INT) | 
 	           (1 << BACK_LOCK_INT) | (1 << BACK_UNLOCK_INT));
 
-	flash_led();
-
 	for (;;) {
+		check_bat();
+
 		switch(cmd) {
 		case LOCK_FRONT:
 			lock();