Re-purposing an Air Wick Freshmatic Compact i-Motion


Step 3: Approach 1: Digitized Sensor Output - Simplest way

Picture of Approach 1: Digitized Sensor Output - Simplest way
To just access the sensor's conditioned digital output, follow the steps below:

    1.  Using a #62 drill bit drill a hole through the circuit board from the copper side at
         the locations marked Sd and Jmp1 in the photo. The locations are indicated
         by a yellow dot. Both locations have a convenient little circular pad that
         we can use. If you can not find a #62 drill bit, see if your hardware store
         carries a #60, this will work. A drill bit especially made for PCB drilling
         works the best.

    2.  Cut the trace that is next to Jmp 1. You might have to click the "i" at the corner 
          of the photo to see the location clearly. 

    3.  Place a wire jumper on the non-copper side of the PCB between Sd and
         Jmp1 and solder.

    4.   Remove the switch from the black female connector's wires. The black
          male connector now has the conditioned digital sensor signal and ground.
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lferrier3 years ago
This is a very useful hack as PIRs can be used for lots of things. I found it incredibly easy to do and use. Thanks so much.
R.A.T.M3 years ago
could you hook the black one to a mortor and whit to power sours and can you chang the timming so it go off evrtime that it senses moten
hoonflap4 years ago
just to verify, the digital signal available after completing step 3 is a solid 5v, correct? or 4.5ish, i see 3 AA's? i want to trigger a 5v reed relay. would i need any additional steps?
Doug Paradis (author)  hoonflap4 years ago
       I believe that your question has 4 parts:

O1:  Can the Vcc for the module be 5V?
 A1:  Yes, I have used the module in circuits from 3V to 6V. I do not know
         the BVCDO of the transistors or the BV rating of the capacitors
         in the module, but they are greater than 6V.

Q2:  Can I drive a 5V reed relay directly from the Sd node on the
   I am going to make 2 assumptions here;
                1. You are using a reed relay similar to Radio Shack part
                     275-232 (i.e., 5V, 250 ohm coil). So you are asking
                     can the Sd node source 20 mA.
                2.  Since the Sd node goes low when the PIR is upset,
                     the coil would be energized most of the time.
        The Sd node is the collector of transistor Q4, which is connected
        to Vcc through resistor R14. R14 is ~100 ohms. At 20 mA, the
       voltage at Sd would be 3V (i.e., Vsd = 5V - (100 ohms * 20 mA)).
       I do not know if this is enough to energize the relay's coil. I would 
       have to try it to find out. If you use the diode protection I mention
       below,  I do not think that you will damage the module.

Q3:  Would I need to do anything else to the circuit?
A3:   You need to put a reverse diode across the relay coil to
         handle the inductive kick when the relay switches.

Q4:  What if that doesn't work?
  I would go through the Instructible a little farther and make the 
        power transistor and its pre-amp accessible (node R). It was
        designed for this type of purpose and has the necessary diode
        in place.  It would also have the additional advantage of inverting 
        the signal so that the relay coil would not be energized except
        when the PIR sensor was upset.