Very retro "Japanese" air purifier.

This unit seems to be very retro. Like it was such a successful product that they didn't feel they needed to change the design. It's very stylish, but has so many bits that it must be expensive to make in terms of plastic mouldings and the assembly time. I'm surprised they haven't streamlined the design down to just a few parts.

The Japanese have always embraced the concept of replenishing the active molecules in air. That might sound a bit quack-ish, but in reality there are certain essential elements of air that have a short half-life in enclosed areas, and need to be created on demand. They are the ones that actively oxidise impurities and deactivate mold spores, bacteria and viruses.

I bought one of these units a very long time ago, and I mean decades ago. I treated it as a novelty until I needed the batteries for something else. Now I understand more about how it works and what it does, I appreciate the design more. Especially in the case of this unit where they have made an effort to keep quiescent (ambient standby) current very low to allow a long battery life.

I didn't really describe the strange battery monitoring circuit enough, so here's some more detail.
When the ozone module is powered the battery monitor is also powered. The 10K resistor acts as a pull-down resistor to the microcontroller's input pin that gets pulled high by the transistor when it's turned on. The transistor starts turning on when its base is around 0.6V below the positive supply rail, and that is scaled down by the bridge of 4K7 (4700 ohm) and 22K (22,000 ohm) resistors which roughly scale the input to 1/5th. That means the transistor will be turned on until the battery voltage drops below around 3V. So the microcontroller can detect the low battery voltage and flash the red warning LED.

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