Hello all. I saw this circuit for an automatic heat detector.

http://3.bp.blogspot.com/-q6eVYCfqB...is6Xo0DFjo/s1600/Automatic+Heat+Detectorw.gif

But i want to replace the relay controlling mechanism with a PIC16F84 microcontroller. So how does T1 and T2 really work? Do they allow current to pass through when there is heat? Do they really have to be configured like that? Can't i use more common transistors?

And for the amplifier T3-T4. Can i also replace them with more common transistors like bc547 or 2n2222?

Also, what's the purpose of the 3V zener?

The description is here http://www.extremecircuits.net/2011/08/automatic-heat-detector.html

 

Hello all. I saw this circuit for an automatic heat detector.

http://3.bp.blogspot.com/-q6eVYCfqB...is6Xo0DFjo/s1600/Automatic+Heat+Detectorw.gif

But i want to replace the relay controlling mechanism with a PIC16F84 microcontroller. So how does T1 and T2 really work? Do they allow current to pass through when there is heat? Do they really have to be configured like that? Can't i use more common transistors?

And for the amplifier T3-T4. Can i also replace them with more common transistors like bc547 or 2n2222?

Also, what's the purpose of the 3V zener?

The description is here http://www.extremecircuits.net/2011/08/automatic-heat-detector.html

The circuit works off the premise that a temperature rise in the transistor whose base is left disconnected causes sufficient current to flow through the drive transistor for the relay...turning the relay on. The rest of the circuit is a voltage regulator and buzzer. It can be anything you want.

I would define your problem (EXACTLY what you want to accomplish) and then post it. The forum, collectively, can then give you input on the best way to go about solving your problem...

 

Could I replace the transistors with ones more common in our area like 2n2222 and bc547?