Today we are going to tear down an automatic room deodoriser. Why?
After walking around the supermarket as one does, pontificating over the need for doughnuts, I noticed this package on sale for eight dollars:
What grabbed my attention was the words “movement sensor” and the price tag. A sensor by itself can cost more. Where’s the catch? I am sure the company makes their money back from selling the refills, in a similar method to ink cartridges and razor blades. Good for them. However, perhaps this can be good for us! So into the basket and home it came.
My flatmates thought it was a lovely gesture to have one in the hallway. Hah! As Dave Jones would say, “don’t turn it on – take it apart!”
So let’s go…
The can of spray went straight into the WC, nothing of interest there. Three alkaline AA cells were included:
Well that’s a good start, you can always use these in a camera or something else. Armed with a philips-head screwdriver and a pair of needle-nosed pliers, the entire assembly came apart very easily and without force. I must congratulate the designers, you almost get the feeling that this is designed to be repaired if broken, and not replaced. The process of dissassembly was quite easy:
The front cover came off quite easily. The switch on the right enables/disables the movement sensor; the LED indicates the repeat mode for the spray; and the black switch controls the duration between sprays – off, 9, 18 or 36 minutes.
After removing the rear panel with four screws, we can see the motor and one of the two PCBs. Two more screws, and we can remove the electronics and mechanical sections:
This is the front-facing part of the motor board. The motor turns one direction then another to have the plastic ‘finger’ push down and release on the aerosol can nozzle. The gear ratios are quite large, allowing the motor to exert quite an amount of torque. The metal base board has some convenient mounting holes as well, so this could be reused easily. If you had a pair of these you could drive something that is quite heavy at a sedate speed.
Here is the main controller board, with nicely colour-coded JST connectors for leads to the motor, power source (those 3 x AA cells, 4.5V) and to the switch that turns the sensor on and off. The underside is very professional, all SMD:
The motion detector’s board plugs nicely into the main board, thanks to the 2×9 pin header and socket arrangement:
Now it is time to see how things work. The first step will be the motor – how much voltage and current does it use? I ran it for thirty minutes at 4.5 volts DC, and the motor body stayed cold, a good sign that this voltage was fine. With regards to current, there are two measurements to take – current while free-running, and under maximum load (i.e. my hand not letting the motor to turn). While running free, the current drawn was 34 milliamps:
… and when I held down the gears so the motor could not turn, the current drawn was 305 milliamps:
So now we have a nice strong motor that can run at 4.5 DC, and draws between 34 and 305 milliamps. That’s a good start. Furthermore, being able to stick the meter display to the desk lamp really makes life easy. Now it is time to investigate the detector. It had a few codes on the PCBs, such as KT-7964, Smart Motion A-06 and RB-S04 which I searched for on the Internet without any luck.
So the next thought was to feed it 4.5 volts DC, and use the Scanalogic2 to analyse any signals or voltages around the PIR sensor module to see what happens. However, the entire system was dead, it would not do a thing. The same problem occurred at four volts DC. No luck either.
So at this point we are at a brick wall, however this is not the end. Research will continue to look for details of the PIR unit, and once it is working independently a new post will be published. This article also shows to me and others that not everything is a success first time. It can be disappointing, however it’s not the end of the world. With every failure comes knowledge which can be used the next time around. So subscribe to the web page updates, and keep an eye out in the future.
So there you have it. I hope you enjoyed reading about this tear down… If you have any questions, please leave a comment (below). We also have a Google Group dedicated to the projects and related items on this website – please sign up, it’s free and we can all learn something.
High resolution images are available from flickr.
Otherwise, have fun, stay safe, be good to each other – and make something!