power output calculation
authorJan "Yenya" Kasprzak <kas@fi.muni.cz>
Fri, 31 Jan 2014 16:10:41 +0000 (17:10 +0100)
committerJan "Yenya" Kasprzak <kas@fi.muni.cz>
Fri, 31 Jan 2014 16:10:41 +0000 (17:10 +0100)
firmware/main.c

index 5c9a566..d35fb21 100644 (file)
 #define WAKEUP_POLL 50 // msec
 #define WAKEUP_LIMIT 5 // times WAKEUP_POLL
 
-/* output power levels */
-#define N_POWER_LEVELS 5
-static unsigned char power_levels[N_POWER_LEVELS] = {
-
-};
-
-static unsigned char power_level = 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
@@ -82,12 +74,38 @@ static volatile uint16_t batt_on, batt_off; // measured voltage
 #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),
+static unsigned char batt_levels[] = {
+       MV_TO_ADC8(3350),
        MV_TO_ADC8(3700),
        MV_TO_ADC8(3900),
 };
+#define BATT_N_LEVELS  (sizeof(batt_levels) / sizeof(batt_levels[0]))
+
+/* output power and PWM calculation */
+#define PWM_TOP        255
+#define PWM_MAX        (PWM_TOP - 8)   // to allow for ADC "batt_off" measurements
+
+/*
+ * The values in power_levels[] array are voltages at which the load
+ * would give the expected power (we don't have sqrt() function,
+ * so we cannot use mW values directly. They can be calculated as
+ * voltage[V] = sqrt(load_resistance[Ohm] * expected_power[W])
+ * or
+ * voltage[mV] = sqrt(load_resistance[mOhm] * expected_power[mW])
+ *
+ * I use 1.25 W as minimum power, each step is sqrt(2)*previous_step,
+ * so the 5th step is 5 W.
+ */
+static unsigned char power_levels[] = {
+       MV_TO_ADC8(1581),       // 1250 mW for 2 Ohm load
+       MV_TO_ADC8(1880),       // 1768 mW for 2 Ohm load
+       MV_TO_ADC8(2236),       // 2500 mW for 2 Ohm load
+       MV_TO_ADC8(2659),       // 3536 mW for 2 Ohm load
+       MV_TO_ADC8(3162),       // 5000 mW for 2 Ohm load
+};
+#define N_POWER_LEVELS (sizeof(power_levels) / sizeof(power_levels[0]))
+
+static unsigned char power_level = 0; // selected power level
 
 /* timing by WDT */
 static volatile unsigned char jiffies, next_clock_tick;
@@ -160,7 +178,7 @@ static void pwm_init()
        // TCCR1 = _BV(CS10); // clk/1 = 1 MHz
        TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
        GTCCR = _BV(COM1B1) | _BV(PWM1B);
-       OCR1C = 255;
+       OCR1C = PWM_TOP;
        // OCR1B = steps[0];
        OCR1B = 0;
        TIMSK = _BV(OCIE1B) | _BV(TOIE1);
@@ -402,8 +420,8 @@ static void status_led_next_pattern()
 {
 
        // for now, display the selected intensity
-       n_blinks = power_level + 1;
-       // n_blinks = battery_level() + 1;
+       // n_blinks = power_level + 1;
+       n_blinks = battery_level() + 1;
        blink_on_time = 0;
        blink_off_time = 2;
        blink_counter = 10;
@@ -425,6 +443,33 @@ static void timer_blink()
        }
 }
 
+static void calculate_power_level()
+{
+       uint32_t pwm;
+       unsigned char batt_on8;
+
+       if (battery_level() == 0 || batt_on == 0) {
+               pwm_set(0);
+               // TODO power_down() after some time
+               return;
+       }
+
+       batt_on8 = batt_on >> 8;
+
+       pwm = (uint32_t)PWM_TOP * power_levels[power_level]
+               * power_levels[power_level];
+       pwm /= (uint32_t)batt_on8 * batt_on8;
+
+       if (pwm > PWM_MAX)
+               pwm = PWM_MAX;
+
+       log_byte(0x10 + power_level);
+       log_byte(batt_on8);
+       log_byte(pwm & 0xFF);
+
+       pwm_set(pwm);
+}
+
 int main()
 {
        log_init();
@@ -435,6 +480,9 @@ int main()
        log_word(batt_levels[2]);
        log_flush();
 #endif
+       log_byte(power_levels[0]);
+       log_byte(power_levels[4]);
+       log_flush();
 
        power_down();
 
@@ -459,12 +507,7 @@ int main()
                        timer_check_buttons();
 
                        if ((jiffies & 0x0F) == 0) {
-                               unsigned char i;
-
-                               for (i = 0; i < BATT_N_LEVELS; i++)
-                                       if (batt_levels[i] > batt_off)
-                                               break;
-
+                               calculate_power_level();
 #if 0
                                log_byte(0xcc);
                                log_byte(i);