Battery check and readme.

1 files changed, 36 insertions, 8 deletions

diff --git a/main.c b/main.c
index d79dc0d..7329e11 100644
--- a/main.c
+++ b/main.c
@@ -33,6 +33,35 @@
 #define PWM_MAX            2500
 #define PWM_TOP            20000
 
+#define VCC_MIN            4900
+
+#define LED_PIN            PB5
+#define LED_DDR            DDRB
+#define LED_PORT           PORTB
+
+/* Measure vcc by measuring known internal 1.1v bandgap
+ * reference voltage against AVCC.
+ */
+uint16_t getvcc(void)
+{
+	uint16_t vcc;
+
+	ADMUX |= (1 << REFS0);
+	ADMUX |= (1 << MUX3) | (1 << MUX2) | (1 << MUX1);
+	ADCSRA |= (1 << ADEN) | (1 << ADPS2) | (1 << ADPS0);
+
+	// https://www.sciencetronics.com/greenphotons/?p=1521
+	_delay_us(500);
+
+	ADCSRA |= (1 << ADSC);
+	while (ADCSRA & (1 << ADSC))
+		; 
+	vcc = (1100UL * 1023 / ADC);
+
+	ADCSRA &= ~(1 << ADEN);
+	return vcc;
+}
+
 int main(void)
 {
 	/* disable watchdog timer */
@@ -42,6 +71,10 @@ int main(void)
 	WDTCSR |= (1 << WDCE) | (1 << WDE);
 	WDTCSR = 0x00;
 
+	/* battery check */
+	LED_DDR |= (1 << LED_PIN);
+	LED_PORT &= ~(1 << LED_PIN);
+
 	/* init input ports */
 	INPUT_DDR &= ~((1 << BACK_LOCK_PIN) | (1 << BACK_UNLOCK_PIN) | 
 	               (1 << FRONT_LOCK_PIN) | (1 << FRONT_UNLOCK_PIN) | 
@@ -69,6 +102,9 @@ int main(void)
 	sei();
 
 	for (;;) {
+		if (getvcc() < VCC_MIN)
+			LED_PORT |= (1 << LED_PIN);
+
 		sleep_bod_disable();
 		set_sleep_mode(SLEEP_MODE_PWR_DOWN);
 		sleep_mode();
@@ -102,24 +138,18 @@ static inline int is_pressed(uint8_t btn)
 
 ISR(FPM_INT_VEC)
 {
-	cli();
-
 	if (fpm_match()) {
 		unlock();
 		fpm_led(BREATHE, BLUE, 1);
 	} else {
 		fpm_led(BREATHE, RED, 1);
 	}
-
-	sei();
 }
 
 ISR(BTN_INT_VEC)
 {
 	uint16_t id;
 
-	cli();
-
 	if (is_pressed(FRONT_LOCK_PIN)) {
 		lock();
 		fpm_led(FLASH, RED, 1);
@@ -137,6 +167,4 @@ ISR(BTN_INT_VEC)
 		} else
 			fpm_led(BREATHE, RED, 1);
 	}
-
-	sei();
 }