Adjusted brightness table, simplify display drawing algo.

* Re-calculate displayed time only ater rtcsync or when time adjusted by
  buttons

README.md

@@ -12,6 +12,8 @@
 * usb phone charger as power supply
 * 2 push buttons
 * 1 on/off switch
+* 1 photoresistor
+* 1 resistor to make secund shoulder of photosensitive "bridge", 10 kOhms, 0.25 watts
 * Gainta G521G enclosure (92x66.5x28мм)
 * 5m power cord
 
@@ -24,12 +26,3 @@
 ### Additional Notes:
 
 My RTC module is not very accurate due to bad quartz chrystal calibration, looks like it is not exactly 32768 Hz and clock runs faster than it should be, giving about 5-8 seconds runaway per day. So i have to implement time correction in software (temperature changes during day/month/year is not very big - about 10 degrees Celsius, so we can use software compensation without thermal compensation).
-
-This project split into 2 branches:
-
-* **default** that contains generic clock without any additional elements
-* **photoresistor** that contains additional hardware - photocell bridge - and software algorithm that compensates ambient light sensed by photocell basing on LED display charachteristics.
-
-### Stable tags for branches:
-v1.6 - default
-v1.7 - photoresistor

simpleclock.ino

@@ -11,6 +11,9 @@
 #include <DS1307.h>
 #include <SevSeg.h>
 
+#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
+#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
+
 DS1307 clock;
 SevSeg Display;
 
@@ -32,6 +35,13 @@ volatile bool compflag2 = false;
 const uint8_t timeSkew = 8;          // assume that clock runs faster than should
 volatile bool timeSkewEven = false;  // comp. 1 additional second per 2 days
 
+/* ambient light compensation aka night mode */
+const int photoPin = A2;
+volatile bool measureAmbLight = true;
+unsigned int ambLight = 0;
+unsigned long previousLightTimer = 0;
+const long refresh_interval = 40;    // refresh rate 25Hz
+
 /* time vars */
 volatile uint8_t mysecond;
 volatile uint8_t myminute;
@@ -48,7 +58,12 @@ void setup()
 	byte digitPins[] = {9, 10, 11, 12};
 	byte segmentPins[] = {2, 3, 4, 5, 6, 7, 8, 13};
 	bool resistorsOnSegments = true; // 8 resistors, 330 Ohms each
-	bool updateWithDelays = false;   // Default. Recommended
+	/* updateWithDelays defaults to false and it is recommended value,
+	 * but i was unable to make my display to change brightness notably with
+	 * recommended value, so i have to use updateWithDelays=true,
+	 * in this case brightness gets changed.
+	 */
+	bool updateWithDelays = true;
 
 	/* without it there is visual bug at 0 o'clock, and in current version
 	 * of SevSeg' setChars() does not dots at all */
@@ -90,6 +105,18 @@ void setup()
 	TCCR1B |= (1 << CS12);    // 256 prescaler 
 	TIMSK1 |= (1 << TOIE1);   // enable timer overflow interrupt
 	interrupts();             // enable all interrupts
+
+/* increase sampling rate of analogRead()
+ * by setting an ADC prescale from 128 to 16, so it takes less time to read
+ * sensor
+ */
+	sbi(ADCSRA, ADPS2);
+	cbi(ADCSRA, ADPS1);
+	cbi(ADCSRA, ADPS0);
+
+	// setup ambient brigtness sensor
+	pinMode(photoPin, INPUT);
+	ambLight = analogRead(photoPin);
 }
 
 ISR(TIMER1_OVF_vect)
@@ -186,6 +213,53 @@ void loop()
 		updateTimeStr(myhour, myminute);
 	}
 
+	if ((currentMillis - previousLightTimer >= refresh_interval) or
+	    (previousLightTimer > currentMillis)) { // millis() reset every ~49 days
+		previousLightTimer = currentMillis;
+		ambLight = analogRead(photoPin);
+
+/* Ambient light compensation
+ * ambLight can be in range of 0..1023, if it 910+, it has point to use
+ * fullbright.
+ * Use table comparsion (not function of ambLight) because of non-linear
+ * charachteristics of led indicator, that cannot be described via simple
+ * formula.
+ */
+		if (ambLight >= 910) {
+			Display.setBrightness(100);
+		} else if ((ambLight < 900) and (ambLight >= 860)) {
+			Display.setBrightness(75);
+		} else if ((ambLight < 850) and (ambLight >= 810)) { 
+			Display.setBrightness(45);
+		} else if ((ambLight < 800) and (ambLight >= 760)) {
+			Display.setBrightness(25);
+		} else if ((ambLight < 750) and (ambLight >= 710)) {
+			Display.setBrightness(18);
+		} else if ((ambLight < 700) and (ambLight >= 660)) {
+			Display.setBrightness(12);
+		} else if ((ambLight < 650) and (ambLight >= 610)) {
+			Display.setBrightness(10);
+		} else if ((ambLight < 600) and (ambLight >= 560)) {
+			Display.setBrightness(7);
+		} else if ((ambLight < 550) and (ambLight >= 410)) {
+			Display.setBrightness(4);
+		} else if ((ambLight < 400) and (ambLight >= 360)) {
+			Display.setBrightness(0);
+		} else if ((ambLight < 350) and (ambLight >= 310)) {
+			Display.setBrightness(-3);
+		} else if ((ambLight < 300) and (ambLight >= 260)) {
+			Display.setBrightness(-6);
+		} else if ((ambLight < 250) and (ambLight >= 210)) {
+			Display.setBrightness(-10);
+		} else if ((ambLight < 200) and (ambLight >= 160)) {
+			Display.setBrightness(-14);
+		} else if ((ambLight < 150) and (ambLight >= 110)) {
+			Display.setBrightness(-18);
+		} else if (ambLight < 100) {
+			Display.setBrightness(-22);
+		}
+	}
+
 	Display.refreshDisplay();
 }
 
@@ -201,5 +275,4 @@ void updateTimeStr(uint8_t h, uint8_t m)
 		Display.setChars(str);
 	}
 }
-
 /* vim: set filetype=cpp: */