Personal air conditioning with MEMS

Finally recycled all the parts.  There wasn't any place to store most of the parts, but there was a desire to see the entire weather wall again.  A lot of time was spent developing the algorithm to sense the LED & emulate button presses to keep the 3 transducers alive.  Doing all 3 on a single microcontroller was a GPIO abstraction buster.

Stored a batch of transducers in various states of disrepair.  They were a big thing for a while.  Then the world discovered how humid it really was, how much scale they deposited, how unreliable they were.  Hard to find any redeeming qualities now.  There have been other big misses.  Something like this, 20 years ago, would have consumed years of effort.  3D printing & development tools cut most of the development down to manely July of 2021.  There was another big push in Sep of 2022.

The decision was made after 3 summers to retire the MEMS swamp cooler on the 4th summer.  The manetenance of the peristalsis pump, water level sensor, & transducers was pretty intense.  Swamp coolers arrived in summer 2021.  The 1st hygrometer arrived in summer 2022, revealing the ambient humidity to be much higher than expected.  It might be the landscaping.  The swamp cooler was only effective below 30% humidity.  The apartment was normally above 30% even on the hottest days.

The arrival of the motorized HDX sprayer in 2024 was the final development which ended the MEMS.  Younger lion didn't realize how much heat he generated pumping a manual sprayer.  Automating it made water sprayers more effective than any MEMS system could ever be.   Even below 30%, the HDX sprayer blew away anything the swamp cooler could do.

Running the swap cooler overnight might have reduced the temperature only 2 deg, but it added a lot of humidity.    If it was below 30%, the ambient air cooled down on its own.  If it was above 30%, the ambient air didn't cool down but the swamp cooler was useless.  It had to be turned off in the morning to try to reduce the humidity.  It also deposited scale on everything.

Clive identified the flyback transistors which keep burning out as A2SHB

There have been transducer arrays, but nothing which includes a decent reservoir.  You're still in need of a small reservoir on a desk with a water level sensor & pump from a bigger reservoir on the floor.

After many consecutive triple digit, low humidity days this summer, it became clear that the transducers had bigger problems  that replacement didn't fix.  They occasionally have to be cleaned of scale.  The transducer which was replaced in june continued to be the problem child.  

That one got a new transducer & board in June but it still tended to get into a state where it would die, the button would have no effect & no amount of whacking got it to start.  It would start once per day & not again.  Replaced its board with yet another board & got some promising results.  These boards are so cheap, they're not worth troubleshooting.  It subjectively looked like insufficient voltage.  The spare board supply is now down to 2. 

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Pointing the transducers sideways more seemed to improve results.  They were originally in a sideways mount so they probably have to be fixed that way instead of on a variable tilt.  The spray would all go sideways or down to keep air bubbles from forming.  The overflow would now run straight down & it would have to be in the center of the sump.  It still needs a gutter to keep the wind from blowing it.

It's going to require a taller stand.  The taller stand needs a counter weight, a way to farsten the water hose & power switch to the base.  

The peak heatwave was intense enough to flatline the humidity even with the swamp cooler on.

After 3 mild & humid years, the weather once again turned back to many consecutive triple digit days with very low humidity.  In these conditions, the swamp cooler has a notable effect  right near the outlet.  The overall room temperature only drops by 1F degree while the humidity rises 5%.  The swamp cooler saw its most use in a long time, with expected failures quickly following.

The 1st thing to go was the pump.  Another tube perished after a year.  Instead of drawing air in, it was letting water out.  It appeared as a small puddle & grew over the next day until the desk was a waterfall.  Expensive stuff got soaked.  Those are going to have to be preventatively replaced every year.

Then a transducer died.  Tried to revive it by unplugging it but forgot this causes the flyback transistors to overload.  The magic smoke came out & it was dead.  It wasn't the 1st fried board.

There's an inventory of spare electronicals because they tend to die randomly.  Got rid of the molex connectors so the transducers can't be unplugged.    This transducer might have gotten silicone grease in its intake.

Upgraded the feed stock to 1 gallon of tap water.  This lasts 12 hours.

The water level sensor managed to not have any issues so far.  In the interest of preserving the water level sensor, it would be best not to put any fragrance in the water, especially oil based. 

Noted the 1mm thick walls are not ideal.  They should really be 2mm thick on the sides.  It also needs a more permanent stand.  It could be a shelf that keeps it on top of the expensive stuff it soaked when the pump died.

Measured it at 6W when not running the pump.

An attempt to reduce the fogging of the windows, this was a fail.  The obvious problem was the water level sensor couldn't detect it & failed negative.  It doesn't conduct electricity.

The less obvious problem was the transducers leaking like crazy.  Maybe electrostatic potential was required to aid the mechanical oscillation in accelerating water or maybe the electrostatic potential was keeping the water on 1 side.  Something about the conductivity of tap water is required for the transducers to work efficiently. 

So back went tap water & it worked perfectly again.  There might be some additive which can create the required conductivity without fogging windows.

A bit surprising that the cleanest water in the world from the mokelumne river still has enough impurities to make a difference.

Fired it up again after many months of winter to find the water level sensor failing low so it didn't stop pumping until timing out & shutting down.  The electrodes were once again eroded & covered in goo. 

The normal practice was to leave it on after the pump timed out, but it doesn't turn off the electrodes.  When it was left on all winter, the electrodes continued electrolyzing & there might have been enough water to barely touch the electrodes, causing them to erode even though it wasn't pumping.  It should turn off the electrodes when the pump times out.

The longer term solution might be a floating sensor.

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35% proved to be the maximum humidity it was worth running at.  Summer 2023 had no major heatwaves & no humidity low enough to run it all night.  Humidity only got below 35% on a few days, then recovered to 40% every night.  The pump needed another tube change.  The sensor still got a coat of slime & algae.

The long awaited pump failure took only 9 months.  Instead of a sudden pouring of water all over the floor, it manifested itself as the motor spinning without moving any water.

The 1st problem noted was the silicone tube being split down the middle & slowly dripping.

The stock motor has a segment of tube between 2 barrel connectors.  To conserve material, don't cut off a segment of good tube to replace the entire segment between the barrel connectors.  Just throw out the bad section & 1 barrel connector. Slide just enough good tube into where the former barrel connector was, every time it wears out.

Once new tube was inserted, the motor still didn't have any luck spinning the rollers.  Either the tube needed some fidgeting to get it loose enough or the rollers are truly worn out.  It eventually started working again.

Most likely, when the tube split it no longer pressed the rollers against the motor shaft enough to get good friction.  

Important to note the direction of pumping when inserting the new tube.  

The transducer replacement, pump repairs, water level sensor erosion, & tank leaks have made this quite a manetenance nightmare.   Every gadget involving water has lived up to its reputation as a manetenance nightmare.  There's still a desire to have it automatically manetain 40% humidity, but investing more time in such a manetenance intensive gadget isn't appealing.

Maybe a lion could make a more reliable pump out of a servo & imperial unit tubing.  The tubing is going to wear out fast, no matter what.  There are still anecdotes of common 3V brushed motors being waterproof.

Knowing the transducers are consumables, a bag of new transducers arrived.  Despite runaway inflation, these are actually still trending towards $1.

https://www.amazon.com/dp/B08HK6Q95R

Knowing they have to be matched to the driver board, it's easier to get them as part of a nano mister.  Then, take out the batteries before they puff.  Those batteries are useful in remote controls since lions have no use for a nano mister.

Based on the shrinking component count, they'r going to have to change to a smaller board.

The next need is to turn off the transducers when the pump times out.  Then, there will hopefully be something which can scent the room unattended.  

A new batch of $1.25 perfumes arrived.  #33 gets a thumbs up from lions.

#20 smells like a dentist so no.

The water level sensor in the newest enclosure had the opposite problem as the previous one.  It constantly failed off, causing the water to overflow.  Stepped down the voltage thresholds to try to overcome what seemed to be a change caused by the new enclosure.