This project belongs to Dim and it can be used to time anything you need, the pcb exposure time, the heating time, just anything. You can set the time between 1 and 90 minutes by pressing the up or down switches. The countdown starts by pressing the on/off switch. By pressing this switch again you can interrupt the process at any time you want. After the time elapsed the timer gives an alarm sounding the end of the process and disconnects the load.
By pressing the on/off switch you reset the timer and it’s ready for another lap. The 2X16 LCD display informs you about the remaining time during countdown and other information’s about the operation of the timer. The image shows the timer board with ATTINY2313 running with internal RC but it’s better to run it with external crystal 8MHZ due to better accuracy. The tiny is pin to pin compatible with 90S but you have to program the appropriate fuses for external crystal. You can check the project’s home page for downloading all the necessary files (eagle, HEX files etc.) and detailed instructions to build the project here(link removed).