Air Wick Advanced teardown - pretty interesting circuitry

A look inside the newest version of the classic Air Wick aroma diffuser, that has been around for many decades in various styles.
These devices use a heater to diffuse a carrier oil with aroma into the air. The classic type has a fixed heating power of a few watts and uses an adjustable shutter to change heat and airflow through the unit to regulate the aroma level.

This unit is very different. It has the same rotating selector, but senses its position in a very novel way, and changes the units behaviour in software. It also has a touch sensor for a boost function, that runs the unit at a higher level for 45 minutes.

Instead of regulating the aroma output in a linear manner, this unit runs the 3W heater in bursts to give a continuous change in the level of aroma emitted. That keeps it more noticeable instead of just merging into the ambient smells.

The circuitry is refreshingly simple, but well designed, although it would have been nicer if the electrolytic hadn't been directly above the power supply's dropper resistors (which dissipate about half a watt each). They are at the base, but do have an airpath out the top of the unit.

The touch sensor with an extra wire is odd. Presumably for cancelling out ambient electrical noise for avoiding false triggering.

I screwed up with the value of the power level potentiometer. Initially I measured it in circuit and got around 10K, but it was being skewed by adjacent components. As indicated on the body of the component it is 104 - so 100K.

The sensing of the mains zero crossing point is interesting. Possibly to turn the transistor on at the zero crossing point, although the load is quite low. But possibly used for a 50/60Hz timing reference. If used for timing I wonder if the frequency is detected in software at power-up.

I'm not sure how the aroma bottle change indicator works. But I'll guess it's purely based on the unit's run time from being powered up.

I do have far too many bottles of the aromas for these. I get drawn in by the exciting names that sell a fantasy aroma-image. I don't use these in my house all the time, but do like a burst of a random aroma from time to time. In the past I've used one in a digital timeswitch to provide a burst of aroma at a specific time of day. It can help keep track of time.

The science of aroma is fascinating. It's used in almost every product to create part of its image or to mask a raw product smell.
Many of the chemicals used have been synthesised from naturally occurring ones, but refined to a concentrated form. Air Wick do imply that they include natural essential oils, but the quantity is probably just a token gesture, as natural oils are very weak compared to the perfected ones.

I'll guess that the carrier in most of these units is a very refined and odorless mineral oil with a ratio of the aroma essences that varies with their concentration. In the generic cheap plug-in air aroma units the level of aroma is usually a fraction of that used in the prominent brands.

When an aroma oil is designed it usually has several layers to it to give it greater complexity. An initial peak of aroma followed by multiple other aroma layers. Each brand seems to have its own key aroma styles.
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