This logic can be used to time a little LED chain when there is only an on/off switch for the 3 AA batteries.
The NPN transistor used is BC550
The 4.5V switch turns the unit on and off.
The switch before the 15k simulates logic level signal from ATTiny85 (or other) output pin.
R values may need to change to match the actual LED configuration.
A sample Arduino sketch:
// LEDtimer.ino
// gah Dec. 02, 2023
// This is supposed to go into an ATTINY85 to make it an on off timer for LEDs
// Remove all console communication first
unsigned long t_now = 0L; // initial value
unsigned long t_8h = 0L;
unsigned long t_16h = 0L;
// We could also have a second on_time in the morning if desired.
int ledPIN = 13;
void setup() {
delay (3000); // security delay
Serial.begin (9600);
pinMode(ledPIN, OUTPUT);
t_8h = 1000L * 60 * 60 * 8; // initial 8h numerical representation in msec
t_16h = 1000L * 60 * 60 * 16; // initial 18h numerical representation in msec
}
void loop () {
digitalWrite(ledPIN, HIGH); // turn power to the LEDs ON
Serial.println ("LEDs are powered ON now\n");
Serial.print ("Elapsed time since start = ");
Serial.println (t_now);
Serial.print ("\tt_8h = ");
Serial.print (t_8h);
Serial.print ("\tt_16h = ");
Serial.print (t_16h);
while (t_now < t_8h) {
t_now = millis();
}
digitalWrite(ledPIN, LOW); // turn power to the LEDs OFF
Serial.println ("LEDs are powered OFF now\n");
Serial.print ("Elapsed time since start = ");
Serial.println (t_now);
Serial.print ("\tt_8h = ");
Serial.print (t_8h);
Serial.print ("\tt_16h = ");
Serial.print (t_16h);
while (t_now < t_16h) {
t_now = millis();
}
// This concludes 1 full day (24 hrs)
// incerementing t_8h and t_16h values now
t_8h = t_8h + 1000L * 60 * 60 * 24;
t_16h = t_16h + 1000L * 60 * 60 * 24;
// then loop untill battery is empty or power switch is pressed
// if overflow occurs during that time you have an excellent battery.
}
