i want to design fire alarm system using AT89c52,
but i dont know how smoke detector works, or what is its behavior when it detect smoke, to enable me to know that there r fire at any place.
what its out voltage in normal state and in fire state??
plz help
There are different types of smoke detectors considering how they must be connected. Basically they are:
4 wires
2 wires
Addressable
Addressable analog
well I believe a good start point is to try 4 wires first. These use 2 wire for power and 2 wires for signal.
In order to do a good circuit you must be able to distinguish three states Normal, Open And Short circuit.
The smoke detector ( 4 wires ) shows no load when they are in normal state and a short circuit when they where activated. Now how do U realize is the line is OK. It is done using and EOL ( End of line Resistor ) If Your circuit sees this R the line is ok and no detector was triggered. If the line is open there is a fault condition. If you see a short circuit a detector is signaling an alarm.
Of course the EOLR must be connected after the last sensor in the line.
You must consider another fault situation. What happens if the line wich feeds the sensors ( 12 or 24 VCC ) is interrupted. To detect this situation you must add a relay which when energized connects the EOLR to the sensors signal line. If power is interrupted a contac opens and you do not see the EOLR. Some sensors models include this relay.