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I thought about this circuit when I heard that a lot cleaning personal in hotels
were either dusting rooms more often than necessary or not enough. I have not yet
built and tested this circuit completely but in concept it should work. The
circuit draws very low current from a +3v battery and could be housed in a package
similar to a small ashtray. The assembly might be placed in a suitable out of the
way area to collect dust. It would alert a maid when it was time to dust the room.
The circuit detects dust with an infrared LED that is pulsed so its light shines
onto a smooth flat plate. Any dust settling onto the surface is detected by a
phototransistor, mounted at a 90 degree angle from the LED. When the dust reaches
a particular level, sufficient light is reflected into the phototransistor to
change the logic state of the circuit to an alarm condition. The alarm output
could be connected to a beeper, a flashing LED or to one of the LED flashing
circuits in this hobby circuit section.
Click on Drawing Below to view PDF version of Schematic
