Simple PCB exposure box timer

Andrian decided to modernize his UV exposure box and on par of this was designing new timer circuit. The concept practically remained same – its rather making it nicer and cleaner. Timer is based on AVR Atmega8 microcontroller, which counts time and displays it on two seven segment displays. AVR is clocked with RTC crystal (32.768kHz). Timer has on-board full-bridge rectifier and 7805 voltage regulator. The lamp load is switched using 5V mechanical relay with basic protection. After timer runs out buzzer alert is raised. Continue reading

Could AVR switch timer be simpler than this?

Timer circuits are handy where you need to switch on or of devices after some time. You just set timer and start. After time elapses microcontroller sends signal to relay and toggles its state. Adrian have built really simple and obvious version of such device. For this he used old good Atmega8 microcontroller, hooked up couple seven segment LED displays. There are enough I/Os on AVR so they are connected directly and no special circuits like transistors are needed. For set and start there are two push buttons. When time runs out microcontroller switches relay and also sounds a buzzer. Continue reading