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smoke sensors

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daniel mandala

New Member
Hie everybody!
I need some information on how a buib(9 volts), an LDR, a variable resistor and maybe an NPN transistor can be used to detect smoke. I wanna build a fire alarm for my home. GOOD LUCK!
 

bogdanfirst

New Member
ok, i think that i know how....i read about it in a book
the principle is that somke keeps the light generated by the bulb and so it doesn't all fall on the sensor
the idea is to build a tube the bulb in one end and the LDR in the other end. then make sone holes at the middle of the tube so that the somke can get in. the idea is to put the device in a place that doesnt have ambient light, because it will not work.
but even this way you still need more components for the detector circuit. like at least a variable resistor and a device to be as an alarm.
but you have to advust the circut so that it will trigger at the smallest amount of smoke, even though the circuit will not be very sensible.
the circuit i saw in the book was a bit more complicated. it used a LED and a modulated light for it so the circuit was imune to the other light as long as it wasnt too bright. i think it used a photo transisto and it worked with IR, not normal leds.
hope that at least i gave you and idea of what you want to do.
 

daniel mandala

New Member
fire alarm

hie guys,
i've found a certain circuit at electronicsworld.tripod.com but i need an explanation on the theory behind the smoke sensing and a step by step detail on how the values of the components can be brought about.
thanks for the help guys. GOOD LUCK!
 

Gene

New Member
If I understand your statement . . .

You have a circuit that you want explained to you by the members of this board but you wont let us see it.

Is that correct?
 

bogdanfirst

New Member
yep! i think that he forgot to mention the link for the circuit or he didnt attach it corectly.....hm.....
hey! daniel mandalaaaaaaaaaaaaaaa!!!!!!!! where is the circuit.....?!?!?!?!?
 
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