Connecting PIRs to a PIC12F675

[Yobortsa]

I'm trying to connect security system PIRs (movement detectors) to a PIC12F675 microcontroller.

Attached is my proposed schematic. Does it look ok?

How do I calculate appropriate values for the resisters?

What transistor should I use?

Does it matter that the transister isn't amplifying the current? (ie. am I correct in saying that Hfe will be less than 1?).

Thanks in advance,

David

 

[Brevor]

If the PIR detectors are located a distance away from the 12F675 it is better to use an optocoupler in place of the transistor. This is to eliminate noise pickup.

 

[colin55]

The PIR has a reed switch. Connect it to the PIC via a small-value resistor as a pull-up or pull-down. A low-value will reduce noise being picked up.

 

[AtomSoft]

my first try would have been like this:

 

[Jon Wilder]

Agreed. NEVER leave the base of a transistor floating. Always reference it to either GND or Vdd via a pull up/pull down resistor. But as colin55 mentioned above, the transistor isn't even needed.