The Air Wick Freshmatic Compact i-Motion air freshener is an intriguing target for re-purposing. It uses a passive infrared (PIR) sensor to detect motion in a room and then increases the rate that it dispenses air freshener. This air freshener sells for $8, but you can sometimes get it cheaper with coupons.
Radio Shack carries the Parallax PIR module for $10. So the question is why bother re-purposing the Air Wick air freshener?
If you just want to replicate the Parallax PIR module, you can modify the air freshener by drilling 2 holes, adding a wire, and cutting a trace. Stopping here, you end up with a can of air freshener, 3 batteries, 2 slide and 1 push button switches, a cool aerosol valve, a medium power PNP transistor, a two wire connector with leads, and a LED. I will show you two ways to do this; the simplest way, and a way to make the module the smallest.
However, If you want to go a bit farther, you can access the amplified analog sensor output as well as the digital signal, and have an externally accessible relay driver, and LED. I describe how all of these features are brought out to an easy to interface connector. You still end up with the air freshener, batteries, switches, and cool aerosol valve.
This last approach is a little more complicated.
Step 1: Avoid the Competition
Make sure that you start with the right product. Glade also makes a motion detector air freshener. It uses considerably different technology.
The Air Wick air freshener uses a PIR sensor. The fragrance canister nozzle is depressed when it is inserted into the air freshener. The fragrance is dispensed by a valve in the air freshener that is activated by a relay driver type circuit. The PIR will detect large movements to about 15 feet with the Fresnel lens attached.
The Glade air freshener uses a light level (shadow) detector and a motor and gear train to depress the canister nozzle and dispense the fragrance. The motion detection on this product has much shorter range than the Air Wick air freshener. It generally sells for $5. It has a nice Sanyo motor that runs on 3 volts.
Step 2: Opening It Up
The photo below shows the parts of the air freshener after you defeat the security screws.
To defeat the security screws, make a driver from a piece of 1/8" steel rod. Grind one end to a triangular shape that fits the screws. The secondary photos below show the driver I made and one of the security screws.
There are 4 security screws holding the case together; 2 that can be seen from the back of the case and 2 inside the battery compartment.
Step 3: 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.
Step 4: Aproach 1B: Digitized Sensor Output - Small Module
This approach is a little more complex than the previous one. We will cut the board to reduce the size of the module. We will have access to just the digitized sensor output.
Note: If you cut the board down, you can not do the modifications to add external
control to the relay driver and LED described later.
1. Flip the capacitor marked C11 so that it points towards the sensor. We are going to
cut near where it originally lays.
2. Strip off the LED, medium power transistor, the large diode, switch SW2 next to
C11, and the black connector.
3. Drill a hole at the location Sd shown in the previous step's photo.
4. Add the two jumpers seen below in the photo.
5. Cut the board a little below the red connector. Sand the cut to make your cut
smooth and straighten any woobles in your cut. You can sand right up to the
edge of the red connector.
You now have access to the digitized sensor output at the outer pin of the white connector and a smaller module.
The picture shows how I trimmed and attached the lens to the module with hot glue.
Step 5: Approach 2: Getting It All - Drilling the Holes
In this approach, we will:
1. Add access to the amplified analog output to the PIR sensor.
2. Have external control to a relay driver.
3. Have external control to a green LED mounted on the module.
4. Bundle all the above into a nice 2x3 connector suitable for
easy interfacing to a microcontroller.
Drilling the holes for the additional access points:
1. Remove the multi-position switch (SW1) located in the lower right
corner when the PCB is viewed from the non-copper side. If you
want to salvage the other switch, remove it also at this time.
2. Using a #62 drill bit, drill holes at the locations shown in the secondary
photo below. There are 11 holes. The spots are marked with yellow dots
in the photo. Take special care at the locations marked LED, R, c1
and c2. These locations do not have a circular pad that we can use.
When drilling these locations, do not drill into the trace, but rather
next to the trace.
3. At LED and R use a dental pick to scrape down to the trace through the
protective overcoat. This overcoat will re-flow with the heat of the solder gun.
Try to use the minimum amount of heat possible to make the connections.
Always be aware of the surface mount components near where you are soldering.
You need to approach the location so as not to accidentally heat them.
Step 6: Cutting the Traces
Cut the traces marked by the 5 yellow lines in the photo below. I used a dremel tool with a pointed bit. Cut into the epoxy for the cut near the hole marked "R".
Step 7: Bypassing C15
To gain the access to the medium power transistor's pre-amp we need to bypass the capacitor marked C15 on the PCB.
Place a piece of wire along the edge of C15 and use it to glob solder across the capacitor.
If the connection is correct you should see 10k ohms between the end of R10 closest to the drilled hole R and the base of the pre-amp transistor. You should also see 100k between the base and the emitter of the transistor (make sure to put the positive lead on the emitter).
Step 8: Preparing the Interface Connector
Our goal is to use the removed switch's contact pads to put in a 3x2 connector that will allow easy access to the module.
In the picture below you can see that all the holes are drilled and all the trace cuts have been made. If you look at the removed switch's pads you can see that 6 have been selected and the outer 4 of the six enlarged. This is because the switches pad to pad spacing is not the same as the connector. I used an #50 drill to enlarge these holes and you can see that I destroyed the pads. I should have used a smaller drill. If you can retain some portion of the pads, the soldering work is much easier.
Step 9: Adding Jumpers and Soldering the Connections
On the traces next to the holes that are not on circular pads (R and LED) you need to expose the trace by scratching off the protective overcoat. I used a dental pick.
Next install jumpers across the non-copper side of the PCB jumpers as shown in the picture below. You can see my pin-out for the 2x3 connector drawn on the board.
A = PIR ampified analog sensor output
D = Digitized PIR sensor output
R = Input of relay driver pre-amp
L = LED cathode through resistor (connect to gnd to light LED)
V = Vcc
G = gnd
Use your multimeter to make continuity checks as you go along. Mine actually went together quite easily. Remember to try to use the minimum of heat and keep away from the surface mounted components and you should have no problems.
Step 10: Testing
When you are finished you can make a few tests to make sure that everything is ok.
Connect Vcc and gnd either through the red connector or on the Vcc/gnd
pins of the 2x3 connector.
1. Insert a female connector with wires into the black socket. Touch the two
wires together. The green LED on the module should light up. Touch the L
pin of the 2x3 connector to the gnd pin and the LED should light up again.
2. Insert a female connector with wires into the white socket. Connect a LED and
series resistor between the two wires. Make sure the LED has its cathode
towards ground. Short the Sd and R connection points in the 2x3 connector.
Now the LED should be on whenever the sensor is not detecting motion.
3. If you have a oscilloscope, you can connect a probe to Sa or Sd and watch
the sensor react to motion. Sa will drift to ~Vcc/2 if there is no motion for a
period of time. Motion will drive it off that bias point either in the positive or
negative direction depending on which way the PIR is upset.
If you pass these 3 tests you are good to go. This project turned out to be a lot of fun.
Do not forget to keep the Fresnel lens to cover the sensor, it improves the sensor's sight. Position the lens over the sensor. You will find that it fits one way very well. To keep it in place, hot glue the tab that sticks over the PCB to the board. You might want to trim the long part that fits over the top of the board.