PC-BASED AUTOMATIC TIME MANAGER
any articles have been published in EFY for control ling devices through a PC’s parallel port or line printer (LPT) port. Here is another project for controlling a school bell or a scheduled shift-timing alarm of a factory automatically. The load connected to the output of the project can be an electric bell or a hooter. The timing can be programmed for every day schedule as per individual requirement. A Windows-based program developed in Microsoft Visual Basic pro-
gramming language is used for controlling an electric bell or hooter through an electromagnetic relay. It has been designed for Windows XP. The graphics have been included so that the master clock shows the real clock time on the PC’s screen. At the same time, it shows alarm clock timing for triggering the timer circuit for activating the bell or hooter. The alarm timings, ‘on’/’off’ controls and their activation sequence can be set by the user as per his requirement through 48 numbers of settings— that is, 24 settings for alarm time display on the screen and 24 for enabling or disabling the timer circuit. The alarm time as well as bell or hooter ‘on’/ ’off’ timer can be set by simple clicking the bigger rectangular box
and a small square box on the top of the rectangular box, respectively. The program output user interface is shown here in the screenshot.
Fig. 1 shows the block diagram of the automatic time manager (ATM) and Fig. 2 shows the circuit diagram of the interfacing unit. Here, we are concerned with only two connections: pin 2 and a ground pin of the parallel port. Pin 2 corresponds to the first data bit ‘D0’ in 8-bit data bus of the parallel port. The whole unit is powered by a 6V DC regulated supply. LED1 is the power-’on’ indicator. IC MCT2E isolates the PC from the main interfacing unit in case any shortcircuit occurs. Thus, it acts as a safety device and protects the PC. IC LM555 (IC2)...