Parallel Port Interfacing and Programming


Posted on Feb 6, 2014

In interfacing AC loads, isolation is very important. This because an interfaced circuit that do not isolates the computer from the AC load have chances that the computer will be so much affected if ever the interfaced circuit will fail or be destroyed. Isolation can be done using a mechanical relay, an opto-coupler or solid-state relay. The figure below shows a 220V AC buzzer interfaced


Parallel Port Interfacing and Programming
Click here to download the full size of the above Circuit.

to the computer. The figure shows a solid state relay that is used as a switch to control a 220V buzzer. When LED lights on, current from AC source will pass through the triac and switches the buzzer on. When LED turns off, the buzzer also turns off because the current will stop flowing in the triac. A solid state relay acts as an interface between the computer and an AC load plug to an outlet. The relay is interfaced D0 of the computer port. Together with the solid state relay is a push button interfaced to S3. Write a program that will switch on the electric fan that is plug to the outlet if the push button is pressed. If the push button is pressed in the second time, the fan will turn off. Pressing the push button in the third time will switch on the fan back and so on. The program should end if a key is pressed in the keyboard.




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