Arduino leave PWM on

Question

I am doing an aquarium light sunrise/sunset. Till now programming wise I only did the sunrise. After running the code the light starts to rise up fine, than at full brightness, it turns off. I want to keep it on after it reaches the 100% pwm and than starts decreasing when it's time to get off. Any help on how to leave the pwm at 100% and than starts to dim when it's time to turn off? I am still new to coding arduino, so explanation need to be for a beginner :P Thanks before hand.

#include <DS3231.h>
//Set Variables
int fadeTime = 15; //Fade Time
int onHour = 12; //Light On Hour
int onMin = 00; //Light On Minute
int offHour = 19; //Light On Hour
int offMin = 00; //Light On Minute
int led = 9; //Set pinout with with PWM
DS3231 rtc(SDA, SCL);
Time t;
void start();
void setup()
{
 pinMode(led, OUTPUT);
 rtc.begin();
}
void loop()
{
 t = rtc.getTime();
 // Send Day-of-Week
 Serial.print(rtc.getDOWStr());
 Serial.print(" ");
 // Send date
 Serial.print(rtc.getDateStr());
 Serial.print(" -- ");
 // Send time
 Serial.println(rtc.getTimeStr());
 if (t.hour == onHour && t.min == onMin) //Check Time
 {
 start();
 }
}
void start()
{
 // Fade script
 for (int i = 0 ; i <= 255; i++)
 {
 analogWrite(led, i);
 delay(((fadeTime * 60000)/306));
 }
}

• Gerben: You need to have the program remember whether the light are ON or OFF. That way you can check the see if they are already on, before calling start.
• Edgar Bonet: The PWM is not supposed to turn off all by itself: last thing you wrote is 255, and it should stay at that level. It looks to me like this is not a software problem, but rather a hardware issue. Just for testing, replace your LED by a low power one (a standard 3 mm or 5 mm LED) in series with a resistor in the 220 Ω – 1 kΩ range. If it works with this setup, then you know it is a power supply issue.

Answer 1

Why not create a global brightness variable (e.g. cBrightness) so that you can adjust the brightness accordingly when the time comes? With a global variable, you can still maintain the brightness of the LED even after it exits the start() function.

For the start() function, you can include one argument (int/bool type variable) in the function to determine when to perform the brightening or dimming of the light depending on the RTC timing.

void start(int st)
{
 if(st==0) 
 {
 //Brightness decrement function here
 }else if(st==1) 
 { 
 //Brightness increment function here
 }
} 

For the brightness decrement function, it is the opposite of the increment function:

for (int i = 255 ; i >= 0; i--)
{
 analogWrite(led, i);
 delay(((fadeTime * 60000)/306));
}

To summarize, the code could look something like this:

#include <DS3231.h>
//Set Variables
int fadeTime = 15; //Fade Time
int onHour = 12; //Light On Hour
int onMin = 00; //Light On Minute
int offHour = 19; //Light On Hour
int offMin = 00; //Light On Minute
int led = 9; //Set pinout with with PWM
int cBrightness = 0; //Current brightness
DS3231 rtc(SDA, SCL);
Time t;
void start(int st);
void setup()
{
 pinMode(led, OUTPUT);
 rtc.begin();
}
void loop()
{
 t = rtc.getTime();
 // Send Day-of-Week
 Serial.print(rtc.getDOWStr());
 Serial.print(" ");
 // Send date
 Serial.print(rtc.getDateStr());
 Serial.print(" -- ");
 // Send time
 Serial.println(rtc.getTimeStr());
 if (t.hour == onHour && t.min == onMin) //Check Time
 {
 start(1);
 }else if (t.hour == offHour && t.min == offMin)
 {
 start(0);
 }
 //Maintains brightness
 analogWrite(led, cBrightness);
}
void start(int st)
{
 if(st==0) //Will decrement in brightness
 {
 for (int i = 255 ; i >= 0; i--)
 {
 analogWrite(led, i);
 delay(((fadeTime * 60000)/306));
 }
 cBrightness = 0;
 }else if(st==1) //Will increment in brightness
 { 
 for (int i = 0 ; i <= 255; i++)
 {
 analogWrite(led, i);
 delay(((fadeTime * 60000)/306));
 }
 cBrightness = 255;
 } 
}