Fire Alarm Using Thermistor

Hi all,
Can i get circuit diagram for fire alarm using thermistor?
I have attached one here.The output device is not only buzzer in my case but also LEDs and exhaust fan serially.So i thought of using PIC microcontroller(I need to use PIC) to drive many devices.Then what should i do to improve the circuit ?

Thanks

The circuit looks like a Schmitt trigger type circuit and your PIC input can be hooked up to the 555's reset pin 4, which is being used to shut off the astable that's used to drive the speaker.

I'm not sure I understand what this circuit is for... would it be easier to buy an off-the-shelf smoke detector and use that detector instead of ad-libbing one (the temperature one would detect fire a lot later than an ionizing or visible smoke detector.)

Detecting a fire by temperature isn't always such a bad idea, if you want to prevent a battery pack or motor from overheating but it's wrong to call it fire dection; the real term is fire prevention.

fire alarm

hi can u say ny applications of da above ckt? nd also da purpose of SL 100B transistor.

This post is 2 years old.
The transistor is to amplify the signal coming out of the 555

The circuit is not a Schmitt Trigger and as with all those Indian circuits, they either never work or are poorly designed.
You need to get a thermistor called a NTC type for the circuit shown.
You then need to experiment with it to see how much it changes per degree.
Place it in the two transistor circuit (you don’t need the diode) and heat up the thermistor.
One of the best ways to heat it up is by touching it with a temperature-controlled soldering iron. With good contact and after quite a few seconds it will be the same temperature as the tip of the iron.
You will get sufficient voltage swing from the two transistor circuit to deliver a HIGH to a PIC chip directly.
Use 10k for R4. You need a 100k base-emitter resistor for T2.

colin55 said:

... as with all those Indian circuits, they either never work or are poorly designed.
...

Click to expand...

Hmm I though it was Cowboy circuits that were hasty and poorly designed??