Vermes
Advanced Member level 4
This device may be useful when you need a handy tool to measure a small part of time without unnecessary precision. Presented timer can measure maximum of 5 minutes with setting each minute. Its accuracy is approximately 0,5 seconds at full 5 minutes.
The system has only one button, a LED indicating set (and measured) time and a buzzer to indicate the end of measuring. There is no main circuit breaker, because after finished work, the microprocessor goes into sleep mode.
How it works:
After pressing the button once, the LED starts blinking every 1 second and measures 1 minute. Each additional pressing the button increases the measured time by 1 minute, and the LED blinks every 1 second so many times, how many minutes are set (which means maximum 5 times). When each counted minute passes, the LED blinks so many times, on which minute it currently is. At any moment of measuring, you can add another minute or two, and you can theoretically extend the countdown time to few hours. After measuring the programmed time, an alarm sound for about 10 seconds, after that the LED lights for 2 seconds and the system goes to sleep. The alarm can be interrupted by a button.
When you do not want anymore to countdown the set time, just press the button more than 5 times. The program understands it as going out of the loop and it ignores the alarm.
This system uses red LED (800mcd) powered by 1k resistor. Current consumption while countdown is approximately 3mA, and when the alarm is on – it rises to about 25-30mA.
Parts of door alarm were used as a housing, buzzer and transformer „T”. The original sound was to loud, so you have to make a simple generator 500Hz – its volume is perfect for that use.
Program was written in Bascom.
Link to original thread (useful attachment) - Minutnik na Attiny13 - kolejna pchełka
