Application of the LM555 timer IC in the monostable mode of operation.
Application of the opto-coupler IC MCT2E.
Interfacing software with hardware through PCs parallel port.
The PC based Automatic Time Manager can be used for controlling a school bell or a scheduled shift-timing alarm of a factory automatically.The load connected to the output can be an electric bell or a hooter.The timing can be programmed for everyday schedule as per individual requirement.The software has been developed using Microsoft Visual Basic and interfaced through PCs parallel port.
No. of ICs used: 3
The PC based Automatic Time Manager uses a Windows-based program developed in Microsoft Visual Basic programming language to control an electric bell or hooter through an electromagnetic relay. 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.
In PC-based Automatic Time Manager circuit, only two pins (namely, pin 2 and ground pin) of the parallel port are being used. Pin 2 corresponds to the first data bit ‘D0’ in 8-bit data bus of the parallel port. IC MCT2E isolates the PC from the main interfacing unit in case any short-circuit occurs. Thus, it acts as a safety device and protects the PC. IC LM555 (IC2) timer is configured in monostable mode of operation. A low transition at its pin 2 will trigger the timer. IC2 timer can be triggered only if the alarm time is set to ‘1’ in enable condition in the software. If the alarm time is set to enable condition, you will get a one-second long beep sound from the PC’s speaker and a high pulse at pin 2 of the parallel port of the PC. A high pulse output at pin 2 of the LPT port will cause momentary glowing of signal LED2 and conduction of transistor inside optocoupler IC MCT2E. The conduction of this transistor sends a low pulse to pin 2 of 555 timer IC2.
When timer IC2 gets triggered, its output pin 3 goes high and holds the relay for 30 seconds. Output pin 3 of timer IC2 is connected to relay driver BC547. The load is controlled through the relay contacts to switch ‘on’ or ‘off.’
The load-’on’ time duration can be set through a 100-kilo-ohm potentiometer (VR1) upto 60 seconds or more. The load (school bell or hooter) is connected to the pole of the relay. When the relay energises, the pole comes in contact with the N/O, and connects 230V AC across the load. This turns on the load for a brief predetermined time set through 555 timer circuit.
Sofware Interface:
Upon connection of the male connector pin 2 (D0) and ground (pins 18 through 25) to female connector on the PC, the ‘ATMINSTALL.zip’ file provided in the CD needs to be unzipped, to get a folder name ATM-Win-Installer. In this folder, a setup program is available and upon clicking the ‘setup’ file, this project will automatically install in ‘Program Files’ folder of Windows with the name ‘Project1’ folder along with other relevant files and drivers.
