home security system using c language only

[anjul agarwal]

i want to build a project on home security system.the thing i had done till is to send current on parallel port.now the problem faced is which sensor is to be used for motion,smoke and to detect fire.
also how to get their acknowledgement back to pc.
plz help me out

[Tomi Engdahl]

Read this document for information on interfacing to parallell port:
http://www.epanorama.net/circuits/paral ... html#input

Parallel port has five input pins that that can be used to interface switches:



If you select sensors that have free floating relay output contacts, then you can put this contact in place of the switch on this circuit. Should work on reasonably short cables (several meters) very nicely (with long cables there is potential for interference because parallel port os quite sensitive).

If the sensors have voltage output, open collector output or are located some distance away, the safest choise would be to put a relay or optocoupler between he sensor and PC. The sensor signa activates that relay/optocoupler control side, and the output of it goes to parallel port circuit in place of the switch.

Those same idas can be also adapted for use with PC joystick port button inputs) or serial port (modem status inputs).