Personal air conditioning with MEMS

Your biggest ally during global warming.

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The journey began with this thing.  It was originally $7 before inflation of course.

Bezos has lower prices in bulk.

They seemed to be a better deal than bare transducers because they came with the electronicals.

Could they be adapted into a low cost cooling system?

The holes weren't very obvious on the outside.

The inside under high magnification showed very clear holes.

It does reduce a lion's temperature, when placed right next to his arm.  It's based on early 2000's MEMS investments, a much more efficient solution than a pump with atomizer.  The internet warned it doesn't last long.  If the water isn't distilled, the MEMs atomizer clogs up quickly.  It does sense when the water runs out & shuts itself off before it overheats.  It also has a 5 minute timer to shut itself off.

It runs for around 7 minutes per tank.  It doesn't seem to leak when it's off.  Only a matter of time before the seals start leaking.  There's a high voltage, alternating current driving the atomizer.  A better solution would have a filter & external hose.  At least it's a starting point for a 3D printed mister using multiple atomizers.

MEMS atomizers seem to have appeared in 2009, near the end of the MEMS boom.  MEMS were the self driving cars of generation X.  They continued evolving into the vaping boom around 2015.  The ideal application was short term use specifically with expensive purpose built fluids.  Along with the essential odor, nicotine or whatever, the fluid could be guaranteed to be free of contaminants so the damn thing wouldn't clog up.

After much designing, a continuous water pump was added.

3 transducers were mounted on a sprayer with a microprocessor to handle timeouts.  It has a drain to handle overflow.

This became the lion kingdom's constant companion during the summer.  As long as there's a supply of dry air, it works.  If no fresh air enters the apartment for several hours, it eventually gets too humid.  It actually continues to provide improvement if hotter air from outside is misted.

  • Distilled water fail

    lion mclionhead10/20/2023 at 05:16 0 comments

    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.

  • Water level sensor death

    lion mclionhead02/17/2023 at 00:46 0 comments

    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.


    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 pump finally dies

    lion mclionhead10/08/2022 at 23:26 0 comments

    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.

  • New transducers

    lion mclionhead09/23/2022 at 01:08 0 comments

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

    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.

  • Enclosure #3

    lion mclionhead09/20/2022 at 23:03 0 comments

    The screw holes appeared to be leaking because they were cracked.  The decision was made to scrap the year old enclosure.

    1 discovery made was ironing does not make a smooth surface for the transducers to sit on.  It leaves blobs.  The best seal is still going to be plumber's grease or balloon rubber.  There's a problem of plumber's grease clogging the transducers.  There was an attempt to make the screw holes more water tight.  The old screw holes were 2 pieces glued together.  The new screw holes are a single piece.

    Instead of clamps, it should have panels screwed in the existing screw holes with scraps of rubber pressing down.

    The drain & pivot are now glued on the enclosure.  The drain needs a channel to glue into.  It continues to be a source of dread.  It needs to move water farther from the stand.  It interferes with the screw holes.  It's hard to model the channel.  Printing temperature is now 230C instead of the 210C originally used.  Getting a good seal with the overlapping areas continues to be problematic.

    New panel was a lot easier to model but looked a lot better.

    Initial results with a new transducer show the transducers are matched to the driver boards, but time will tell.  The new drain doesn't work as well as the old one.  It needs to be wider & extend more in front of the pivot point, but so far no drain has ever been needed.

  • Transducer blues

    lion mclionhead09/10/2022 at 21:39 0 comments

    A subtle detail was the failure of transducer #3.

    A new one went in but still yielded a short period of low flow, then shut down & leaked lots of water.  There might be a bad screw hole leaking water.

    The original transducers have lots of scale but flow like they were new.  Transducer #3 got a new driver board which didn't make any difference.  The leading theories are a bad cable or the transducers having to be matched to the driver boards.

    A new enclosure was already conceived to move the transducers closer together.  To do this, they got a common cap which would have required removing 6 farsteners to access 1 transducer.  Obviously, it's not practical in a world where transducers are consumable & must be replaced 1 at a time.  The mane desires would now be thicker walls to try to reduce the water leaks, possibly more transducer spacing to keep water from landing back on the other transducers, possibly a 4th transducer.

  • Water sensor blues

    lion mclionhead09/08/2022 at 19:56 0 comments

    There was this idea of letting the vapor escape instead of condense, but it still failed on.  It leaned towards splashing getting water on the standoffs.

    Then this idea came along.  This showed the spacing might be 2-3mm away from enough to overcome surface tension. It would require tweeking the ADC threshold.  It is a fiddly value.  There's mounting the electrodes sideways & opposing.  The idea with vertical electrodes is the ADC value rises as the water level rises.  Horizontal electrodes would give a single ADC value for all water levels.

    Another sensor was made with 2mm wider spacing, but by then temperatures fell below what was causing the problems.  

    For future lion, we have the typical life of the sensor flipping high when the tank fills, slowly dropping as the tank empties, flipping low when the sensor dries out.  The spacing didn't impact the readings.

    It was noted that an electrode was eroding, so it was swapped out.  Gold plating only buys time.  This led to suspicions the sensor might fail off one day.

    The decision was finally made to make the pump timeout after 90 seconds, to avoid emptying the 5 gallon tank on the floor.  It typically takes 40 seconds to fill the tube & transducers.

    The new sensor is a lower profile.

  • The great heatwave of 2022

    lion mclionhead08/12/2022 at 03:20 0 comments

    This proved its worth during the great heatwave of 2022.

    Outside - inside temperatures tell the tale of heat turning into water vapor when compared to the days before swamp cooler.  Higher is better.

    Comparing the great heatwaves of 2020 & 2022, the humidifier kept the inside 2-4 degrees cooler than what it would have been.  Indoor temperature peaks happened during the driest time of day when the humidifier is most effective.

    Humidity with the swamp cooler on was 20-30% during the evenings.  It would have to be turned off during the mornings, when humidity hit 38%.  

    The ideal position is right on top facing forward.  Lacking a place to mount it, the next best place is high on the side.  The problem is the airflow is clockwise so this position gets it pushed down into the speaker.   A tower fan is easier to mount on top of.  The current fan was a cheap stop gap solution.  

    Sadly, the water level sensor started routinely failing on in temperatures above 90F.  

    This didn't work. Water bridged the plastic standoffs.  It seems to be condensation between the standoffs in higher temperatures rather than incoming water clinging to the lid.  It might also be shaking of the desk splashing water on the standoffs.  It's going to need a more clever standoff design, since the spacing of the electrodes is proving enough.

    Perfume & essential oil leave a lot of residue.  

    A 5 gallon tank is your biggest ally in global warming, but lions only filled it to 1 gallon for fear of a leak.  The humidifier stayed on all night during the great heatwave of 2022.  It would not be affordable to add fragrance to these quantities.  Some highly desirable features are reading the hygrometer, turning off when humidity is over 38%, a timer for using a 32oz tank.  Lions seem to fall over above 38% humidity.

  • The truth about vanilla

    lion mclionhead07/17/2022 at 21:28 0 comments

    A few days revealed why vanilla is cheap.  It's just corn oil.  It made everything smell like popcorn, depending on the concentration.

    Got every perfume in the Bidie buck store. The sprayers are good enough that prying them off & developing stoppers won't be necessary.  They all say flammable but the amount of dilution should defeat the problem.  Anything is better than eau de apartment.  The apartment started out smelling like indian curry.  We've come a long way.

    The weak link was #24.  That smelled like orange juice.  The rest smelled great in the swap cooler, as well as the legerdemanne.  They're much more diluted than expensive stuff.

    The floor fan was replaced by a desk fan.  The optimum placement of the swamp cooler is right in front of the fan, pointing diagonally into the fan.  It can't spray from behind the fan without condensing on the grille.  Ideally, the water collection bin would be right below it & the whole thing would be on a big stand so it could go higher.

    There is now algae growing in places where the PLA is slowly leaking & water tends to accumulate.  There is a slowly evolving design for a new enclosure.  The mane problem is creating a taller stand for use with the desk fan.

    The hydrometer allowed a big increase in use of the humidifier.  Lions have had much better skin since the hydrometer arrived.  

  • Essential oil

    lion mclionhead06/15/2022 at 04:29 0 comments

    The lion kingdom added a 2mm puddle of perfume on the bottom of the gatorade bottle & filled it with water.  $1.25 store perfume in the swamp cooler is quite pungent, but it didn't clog it. It already handled tap water without getting clogged.  The mane problem is extracting enough perfume from the dispenser. The best solution is peeling off the spray device & fabricating a stopper for it.  The glass bottle is easy to pour.

    The $1.25 perfume ended up being a surprisingly powerful sedative.  Lions never knew anyone who wore the mind numbingly sleep inducing perfume of school classrooms & always figured it was super expensive.  That super expensive perfume would still be ideal.

    $1.25 is believed to last about 30 hours, so it's still not free in lion terms.  It's probably equivalent in odor per price to incense.  It can't be thrown away like water.  In order to get the right concentration, the diluted form can't be refilled until it's empty.  It needs a bottle top if it is to be stored in the diluted form.

    After using  up the perfume, the next experiment was air wick, the cheapest essential oil made.

    These are intended to be heated & evaporate passively.  The wick & plastic piece can be removed with some prying.  The oil can then be poured out.  The oil can't be poured out if the plastic is still in place.   The same concentration as perfume yielded an acceptible odor but didn't clog.

    There is a case for making a 45 minute timer to run it instead of incense at night.    It would use a lot less space than incense, but it would be too cold in winter.

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