Added more robust low voltage detection, now it only tests each 200ms…

… while motors are not actuated. Added NMEA message PFBSP (System Parameters) to allow changing the minimum voltage threshold. Changed NMEA message id PFBCO to PFBCP (Communication Parameters). Removed undocumented values from NMEA message PFBST.

firmware/main.c

@@ -59,7 +59,7 @@
 #define STATE_WATCHDOG			3 /* no validated nmea packets received for the past 0.2 seconds */
 #define STATE_LOWBAT			4 /* battery voltage too low */
 
-#define VOLTAGE_MIN			682 /* minimum voltage */
+#define VOLTAGE_MIN_DEFAULT		682 /* minimum voltage */
 
 /* signal led defines */
 #define LED_STATE_OFF			0
@@ -95,12 +95,14 @@ unsigned short nmea_wd; /* NMEA watchdog counter */
 unsigned short pfbst_interval; /* PFBST interval (20-10000) [ms] */
 short nmea_ticks_l, nmea_ticks_r;
 
-/* adc variables (8 bit [0;255]) */
-volatile unsigned short adc_data[ADC_NUM]; /* adc data variables */
+/* ADC variables (10 bit [0;1023]) */
+volatile unsigned short adc_data[ADC_NUM]; /* ADC data variables */
 volatile unsigned char adc_ch; /* current adc channel */
 unsigned char adc_ports[ADC_NUM]; /* maps to ADC ports */
 
 unsigned short voltage;
+unsigned short voltage_min;
+unsigned char battery_low_warning;
 
 /* wheel variables */
 extern char pid_enable;
@@ -149,6 +151,17 @@ void adc_init (void)
 	ADCSRA |= BV(ADSC); /* request ADC conversion */
 }
 /***************************************************************************/
+void voltage_update(void)
+{
+	if (spd_set_l == 0 && spd_set_r == 0) /* only test when standing still */
+	{
+		if (battery_low_warning == false && voltage < voltage_min)
+			battery_low_warning = true;
+		else if (battery_low_warning == true && voltage >= voltage_min)
+			battery_low_warning = false;
+	}
+}
+/***************************************************************************/
 void led_update(void)
 {
 	/* led_state = state; */
@@ -227,14 +240,19 @@ void nmea_rx_parse(void)
 		if (rx_ite != -1)
 			spd_set_r = nmea_rx_next_val()/pid_rate;
 	}
-	else if (rx[3] == 'C' && rx[4] == 'O') /* parameters */
+	else if (rx[3] == 'C' && rx[4] == 'P') /* Communication Parameters */
 	{
 		rx_ite = 5; /* jump to first value */
 		pfbst_interval = nmea_rx_next_val();
 		if (rx_ite != -1)
 			nmea_wd_timeout = nmea_rx_next_val();
 	}
-	else if (rx[3] == 'W' && rx[4] == 'P') /* parameters */
+	else if (rx[3] == 'S' && rx[4] == 'P') /* System Parameters */
+	{
+		rx_ite = 5; /* jump to first value */
+		voltage_min = nmea_rx_next_val();
+	}
+	else if (rx[3] == 'W' && rx[4] == 'P') /* Wheel Parameters */
 	{
 		rx_ite = 5; /* jump to first value */
 		pid_enable = nmea_rx_next_val();
@@ -285,16 +303,14 @@ void nmea_tx_status(void)
 	nmea_ticks_r = 0;
 	nmea_tx_append_short (ticks_l);
 	nmea_tx_append_short (ticks_r);
-	nmea_tx_append_short (pid_rate);
-	nmea_tx_append_short (spd_set_r);
-	nmea_tx_append_ushort (voltage); /* battery voltage 10-16V */
+	nmea_tx_append_ushort (voltage); /* battery voltage [0;1023] */
 	tx_len--; /* delete the last comma */
 	nmea_tx();
 }
 /***************************************************************************/
 void state_update(void)
 {
-	if (voltage < VOLTAGE_MIN)
+	if (battery_low_warning == true)
 		state = STATE_LOWBAT;
 	else if (nmea_wd > NMEA_WD_TOUT)
 		state = STATE_WATCHDOG; 
@@ -352,6 +368,7 @@ void sched_update (void)
 		{
 			button_update();		
 			led_update();
+			voltage_update();
 		}
 	}
 }
@@ -371,6 +388,8 @@ int main(void)
 	pfbst_interval = 100; /* send $PFBST at 100 ms interval */
 	nmea_wd_timeout = 1; /* set PFBCT watchdog timeout to 100ms */
 	nmea_wd = NMEA_WD_TOUT+1; /* make sure we begin in watchdog timeout state */
+	voltage_min = VOLTAGE_MIN_DEFAULT;
+	battery_low_warning = false;
 	state_update();
 
 	sei(); /* enable interrupts */