This library was created to blink a LED without needing to use a timer. Simply let the library know how long the LED needs to stay ON and OFF (in milliseconds), and call .blink() as often as possible.
#include <TimedBlink.h>
TimedBlink monitor(LED_BUILTIN);
void setup() {
Serial.begin(9600);
pinMode(LED_BUILTIN, OUTPUT);
monitor.blink(150,50); // LED on for 150 ms and off for 50 ms.
}
void loop() {
monitor.blink(); // Call this as often as possible
}