Digital Timer can be built by using PIC16F876A micro-controller and a few additional components. The schematic is similar to Fan Speed Monitor Design. 3×4 Keypad and 5V Relay
A simple upgrade to current design can be made by increasing the timer range. It can be done for example by adding another function to generate 1 min counts instead of seconds or by enabling 4th digit to achieve 9999 max reading. You can download timer source code here. Additional information about interfacing 7-Segment Displays can be found in 7-Segment LED Display with I2C post and 7-Segment Display with SPI article. Design schematic diagram and a short video demonstrating circuit operation are available on the next page.