A Small Victory: Modifying the Parallax PIR

Ahead of using the Parallax PIR for a project, I had a problem.  

OK, first: A PIR is a Passive (or Pyroelectric) InfraRed Sensor.  It detects motion by looking at heat (IR) in front of it.  You have probably seen one of these in an outdoor light that turns on when you walk by.  The one I bought is just the detector module (made by Parallax).  Costs $10.  It signals through a connector and lights up with a red glow when it detects motion.

SO, the project.  I am trying to use it to monitor my cat’s movements during the day and here is the problem: the glow that turns on inside the device catches her attention, wrecking the objectivity of this observer.  This cat and I have played one too many hours with the red laser pointer and thus, she love red lights.

I would like to turn the glow off.  

The dome appears to be glued closed and I do not want to crack it getting to the LEDs.  The other option is to modify the PCB and deprive the LED of power.  But how?

I wrote Parallax an e-mail, explained the problem, and without a whiff of legaleze, they just sent me the schmatic for the device.  Just like that.

Awesome.  Above you can see that the LEDs in question (labeled in yellow) and the connection that needs to be broken (orange arrow).  Follow the little pin through the board and the trace that feeds R10 is easily seen on the front of the device.  I scratched through it with an Exact-o knife and broke the connection.

Now the device works the way I want it to: it signals through its connectors without lighting up.

Hat’s off to Parallax for open sourcing it!  Now to build the rest…

(Oh, and modify your own PIRs at your own risk, of course!)