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New mapping function for ambient light sensor

This commit is contained in:
Admar Schoonen 2012-01-07 23:46:43 +01:00
parent 05272f8ee3
commit cad09796c2
2 changed files with 57 additions and 11 deletions
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35
wordclock/lightlevelmapping.m
View File

@ -1,4 +1,39 @@
function lightlevelmapping()
MINBRIGHTNESS = 1;
MAXBRIGHTNESS = 10;
LIGHTSENSOR_BOTTOM = 0;
LIGHTSENSOR_TOP = 150;
x = [LIGHTSENSOR_BOTTOM - 10:LIGHTSENSOR_TOP + 10];
b = zeros(size(9));
LIGHTSENSOR_ALPHA1 = 0.02;
LIGHTSENSOR_ALPHA2 = 0.20;
a = LIGHTSENSOR_ALPHA1 * LIGHTSENSOR_TOP / log(LIGHTSENSOR_ALPHA2 / ...
LIGHTSENSOR_ALPHA1);
b = LIGHTSENSOR_ALPHA1 / a;
c = MINBRIGHTNESS - a;
y = a * exp(b*x) + c;
y_ = round(y);
[x; y_]
figure
plot(x, y, x, y_);
A = axis;
A(1) = LIGHTSENSOR_BOTTOM - 2;
A(2) = LIGHTSENSOR_TOP - 2;
A(3) = MINBRIGHTNESS - 2;
A(4) = MAXBRIGHTNESS + 2;
axis(A);
grid on
return
function lightlevelmapping_old()
MINBRIGHTNESS = 0;
MAXBRIGHTNESS = 10;

33
wordclock/wordclock.ino
View File

@ -75,7 +75,12 @@ void SWversion(void);
#define LIGHTSENSOR_BOTTOM 0
// top of light sensor (ambient light values at or higher than this level will
// be mapped to MAXBRIGHTNESS)
#define LIGHTSENSOR_TOP 900
#define LIGHTSENSOR_TOP 150
// slope of mapping function at bottom
#define LIGHTSENSOR_ALPHA1 0.02
// slope of mapping function at top
#define LIGHTSENSOR_ALPHA2 0.20
// weight for exponential decaying averaging (actual weigth is 2 ^ LIGHTSENSOR_WEIGHT)
#define LIGHTSENSOR_WEIGHT 4
// base of exponential mapping (must be > 1)
@ -87,7 +92,7 @@ void SWversion(void);
// start MAXBRIGHTNESS at DAYLIGHTHOUR (7 am)
#define DAYLIGHTHOUR 7
// NIGHT Brightness setting 0 = off, N_PWM_STEPS - 1 = full
#define MINBRIGHTNESS 2
#define MINBRIGHTNESS 1
// start MINBRIGHTNESS at NIGHTLIGHTHOUR (7 pm)
#define NIGHTLIGHTHOUR 19
@ -180,6 +185,9 @@ void setup()
{
int n;
// a, b, c and e are needed to compute lookup table for ambient light sensor
float a, b, c, e;
// initialise the hardware
// initialize the appropriate pins as outputs:
pinMode(LEDClockPin, OUTPUT);
@ -245,6 +253,12 @@ void setup()
}
// compute ambient light level to brightness level mapping
a = LIGHTSENSOR_ALPHA1 * LIGHTSENSOR_TOP / log(LIGHTSENSOR_ALPHA2 /
LIGHTSENSOR_ALPHA1);
b = LIGHTSENSOR_ALPHA1 / a;
c = MINBRIGHTNESS - a;
e = 2.718281828459045297;
for (n = 0; n < sizeof(ambient_light_to_brightness); n++)
{
if (n <= LIGHTSENSOR_BOTTOM)
@ -254,18 +268,15 @@ void setup()
else
{
ambient_light_to_brightness[n] =
round( pow((double) LIGHTSENSOR_BASE, (
(double) brightness_per_unit_light * ((double) n - (double)
LIGHTSENSOR_BOTTOM) / (double) (1 << LIGHTSENSOR_SCALE))) / pow((double)
LIGHTSENSOR_BASE, (double) (MAXBRIGHTNESS - (double) MINBRIGHTNESS)) *
((double) MAXBRIGHTNESS - (double) MINBRIGHTNESS) + (double) MINBRIGHTNESS );
/* Serial.print(n);
Serial.print(": ");
Serial.println(ambient_light_to_brightness[n], DEC); */
round(((float) a) * pow(e, ((float) b) *
((float) n)) + (float) c);
if (ambient_light_to_brightness[n] < MINBRIGHTNESS)
ambient_light_to_brightness[n] = MINBRIGHTNESS;
if (ambient_light_to_brightness[n] > MAXBRIGHTNESS)
ambient_light_to_brightness[n] = MAXBRIGHTNESS;
}
}
// determine whether we are running on old or new hardware
// old hardware tied the push buttons to ground using 4k7 resistors
// and relied on the buttons to pull them high