![]() ![]() With MIN and SEC buttons we can increase/decrease the value of an internal parameter thus slowing down or speeding up the timer. When shorted, the timer enter in adjusting mode. Jumper J1 is for calibrating of the timer. In my case there will be connected a transistor which will switch on and off the UV exposure box. With this pin we can operate some external circuitry. When timer is counting down - RB7 (pin 13) is high and when the timer is stopped - RB7 is low. When the timer reach 00:00, the buzzer sounds 3 short and 1 long beeps and the LED lights up.Īfter this any of these three buttons will reset the status and LED will switch off. ![]() Pressing MIN and SEC buttons simultaneously will reset the timer. "MIN" and "SEC" have repeat functionality. Seconds goes up to 59 and then starts from 0. Minutes may go up to 99 and then starts again from 0. "START/STOP" is for starting and pausing the timer. There are three buttons to operate the timer: "START/STOP", "MIN" and "SEC". My programming abilities are little rusty, but I think the final result is quite good. The schematic uses the internal oscillator of the microcontroller which is enough accurate for my purposes, but as the pins 15 and 16 are left unoccupied, there can be connected external quartz resonator with better accuracy.Īs I said, this project is based on an existing project, but actually my schematic is quite different and the code was almost completely rewritten. ![]()
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January 2023
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