This simple and flexible timer is more accurate than the real-time clock of the computer used for the purpose. It can be used in laboratories, dark rooms, kitchens, and for competitions in educational institutes. The program written in Q-Basic is self-explanatory. Generally, a universal timer provides the facility for switching on an electrical/electronic device after elapse of a certain time period, say, 5 minutes. The software does the same job here.
Universal timer operation
When the program is executed, it displays 0:0:0 on the monitor, indicating 0 hour, 0 minute, and 0 second. The display time 0:0:0 is increased by 10 seconds each time function key F1 of the computer keyboard is depressed. So by depressing function key F1 the required time is set for which the electrical or electronic device is to be switched on. However, in debate competitions the time allowed for a candidate to speak is filled the way it is discussed above. The program may be changed as indicated by REM statements and the single quote (‘) in the beginning of a program line may be accordingly removed in the program.
Now, after setting the time in the manner as discussed above, function key F2 of the computer keyboard is depressed to switch on any device. Simultaneously, the countdown of the time in the display box starts. The device will remain on until the display box shows 0:0:0 and then it will get switched off. The figure shows the relay interface circuit connected between D0 line (pin 2) and ground line (pin 25) of 378H output port of LPT1 printer port of the computer.
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