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.

  • New water level sensor

    lion mclionhead08/25/2021 at 22:55 0 comments

    So the peristaltic pump runs 90% of the time, unlike the 3D printed pump which ran 10% of the time.  The reason is it's so slow it turns off as soon as the water level is high, rather than overshooting like the 3D printed pump.  There could be a way to delay the on event, based on prior knowledge of the mist consumption & tank size.

    Also noticed the mist smells like sawdust if it's off for several weeks.  The odor goes away after a few minutes, but reminds lions of hikers who died from algae poisoning.  There's no visible algae in the tank & nano misters have been sold for years.  It could also be the smell of forest fires getting enhanced by the water droplets.

    The water level sensor started failing a lot more with the peristaltic pump.  The leading theory is it had more deposits because the water never fully covered it.  The overshooting pump might have rinsed off deposits.  There were no visible deposits on it, but a new water level sensor was created anyway.  This one uses fully gold plated, 2mm bullet connectors.  They should be easier to clean, at least.

    Resistance sensors are always going to be problematic.  The next idea was a bulky floating sensor with optical interrupter & a lot more wires.  The tank is too small to generate enough buoyancy to flip a switch.  A simpler sensor would be a floating magnet with hall effect sensor, but magnets don't float.  

  • Death of a pump

    lion mclionhead07/31/2021 at 22:05 0 comments

    The gatorade bottle & level sensor worked well, after the initial problems with corrosion & siphoning.  Sadly, 1 month submerged turned the motor into a rusted mess.  The motor bearings & set screws rusted.  All the steel farsteners rusted.

    It was exactly as feared.  There was a momentary push for another novel pump design.  Anything spinning would require expensive stainless steel bearings.  Reciprocating pumps were already tried.  

    The dream of a 3D printed pump was busted, but only at a certain price.  If the steel motor parts were all replaced with stainless steel & the electromagnets had 3D printed cores, it might work.  The lion kingdom would need machine tools to fabricate a custom motor.  It would cost more than a commercial pump & be less efficient.

    The lion kingdom was out of time, so just ordered a peristaltic pump.  It would be self priming, immune to siphoning, & dry.  It could be in the same enclosure as the electronicals.  The water bottle could be any height.  Eventually, the silicone tube would wear out & empty the entire bottle on the desk, but it was good enough for at least a summer.

    The heart of the peristaltic pump is a planetary gear where the sun gear is the motor shaft, the planet gears are rollers, & the ring gear is the tube.  There is a high gear reduction between the motor shaft & tube.

    The rollers are precisely sized to press the tube closed & press the motor shaft.  

    There is a retaining ring to keep the rollers pressed on the motor shaft in the 1 part where there is no tube.  Some more clamps keep the tube from getting pushed out.

    Water drips out at the full 12V, 200mA.  It's nowhere close to a much smaller 3D printed impeller pump.  

    The air conditioner finally got its final board, made of a PIC18F1320.  It had to use the ADC to read the LED voltages since they don't go to 0.  The peristaltic pump uses a MOSFET instead of a 3 phase motor driver.  The 5V regulator got replaced by a much more efficient buck converter.

    The water level sensor didn't work anymore from deposits & had to be cleaned.  1 transducer board burned out because the transducer wasn't connected.  They can't be turned on without the transducers.

    The 5mm hose for the pump is incompatible with the locally sourced 1/4" fittings for drip irrigation hose.  The AC needs a new elbow fitting & inlet for 5mm hose.

    The transducer tank is really loose on the stand.  It should be glued to its drainage plate instead of bolted as it currently is.  The original idea was to make it slide up & down the drainage plate, but it proved easier to print a new stand to adjust height.

    It burns .5A when pumping & .3A when just spraying.

    The gatorade bottle now just has a hose.  

  • The transducers leak

    lion mclionhead07/30/2021 at 19:15 0 comments

    So over time, the transducers start leaking when they're off.  There's some kind of abrasion widening the holes.  The reservoir is always empty in the morning.  At least the leaks keep scale from accumulating.

    Another stand update shifted the leaking transducers farther back & opened the door to adding horizontal farsteners to the base.

    In a year, lions have managed to routinely create models which use minimal material & don't require supports.

    Ordinary paperclips have worked well.

    Didn't expect it to ever route all the overflow & leaks to the container.  The last few models have eliminated any water spraying on the table.

  • Pole stand

    lion mclionhead07/28/2021 at 20:40 0 comments

    It became clear that air has to pass under the transducers to keep the mist from getting blown down & to make room for a fan.

    The transducers ooze a little when they're turned off, but not enough to require a tub.  Most of the overflow comes out of the cap when the water level sensor fails or the gatorade bottle is too high.  Because of the airflow situation, a pole stand which catches the overflow just from the cap & directs it down to a tub would be ideal.

    The ideal angle & height of the transducers has evolved to a fixed position which simplifies matters.  The overflow always goes out the back.   There could be a flat funnel with a channel to direct the overflow down the back.

    10 meters of filament later, the stand emerged.

    The mist still went down, but more of it is evaporating.  At least it directed all the overflow into the tub.

    It should sit farther back so the transducer dripping gets captured.  There's no easy way to farsten the stand to the tub.  The base needs a vertical bit which can farsten horizontally.

  • Enclosure update 2

    lion mclionhead07/27/2021 at 20:58 0 comments

    Electronical placement is heading in the right direction.  Cutting down the tub got more water into the air.

    The tub could go all the way back, with all the electronicals vertical.  It's stable enough to not need ballast.

    Getting the spray to go in the air instead of on the table proved to be a big problem.  Most of the water ends up going down.  Air currents around the stand blow down.  The stand creates more of a vortex than the tripod.  Ideally, air would flow under the transducers or the transducers would stick out more.  

    Aiming it perpendicular to the airflow gets a little more into the air.

    A useful feature would be selecting how many transducers to run.  The software for turning off would then be useful.

  • Enclosure design

    lion mclionhead07/18/2021 at 21:52 0 comments

    The 3 transducer model has proven game changing up to 90F & the transducers haven't died from being run continuously, so work began on a better enclosure.  

    3D printed enclosures this big are real expensive, so it was back to coroplastic & duct tape.

    So the high voltage lines cause the water level sensor to fail high.  They have to be separated.

    The print statements in the interrupt handler cause PWM to fail even though they're not blocking.  Such things happen at 1.25 MIPS.  Lions have a strange fascination with running their micros as slowly as possible to use the least amount of power.

    It pumps a lot of water with 3 transducers.

    It proved easier to not use the switch & just power the thing off.  There's a long delay for the ESC to start, but it's proven less hassle.  All the software related to shutting down ended up worthless.

    The amount of consumables used & the velocity of the water spray got lions wondering if a piezo rocket engine could be built.  Anything kinetic is going to be far below ion engine efficiency, but would use a lot less power.  It's too fragile to use as a fuel injector.

    An enclosure is desperately needed.  The mane needs are stabilizing it from falling over, catching overflows, adjusting height & angle.  The best stability comes from routing the tube out of the bottom & sideways.  The water level sensor still has to be vertical.

    It is believed the existing PLA part could stay as it is & be attached to some kind of coroplastic stand.  The  PLA part needs a small overflow trap under it, with a way to pipe the water to another container.  The best place for the electronicals would be behind the PLA part.  The stand needs to be weighed down.

    More height is better.  Too low & it dumps water on the table.  Too high & the monitor can't fit over it.  Experience has shown it dumps a lot of water overboard.  If anything gets in front of the transducers, a puddle soon forms.

    No matter what lions do, the mist gets pulled down to the table.  It probably needs a fan blowing up.

    A lot of scale is building up.

  • Triple Transducer

    lion mclionhead07/11/2021 at 06:57 0 comments

    It could finally detect if the transducer was running by reading the LED voltage, then press the button by grounding the button.  This allowed the mist to be controlled with a switch.  The mane problem is the LED has to be debounced for 3 seconds, in case it flashes.  If the switch is toggled too fast, it takes a few seconds for the transducer to match the desired state.  Fortunately, the switch's physical position is always eventually matched by the transducer.

    When the 5 minute timeout shuts it down, it senses the LED going out & presses the button to restart it. 

    The water level sensor was well & truly corroded after just 1 day.

    The next step was gold plated copper.  Helas, this still built up a layer of scale.  The problem is the water level constantly rises & falls, depositing a layer of stuff every time.  The hope is the resistance eventually levels off.

    The 2 wire sensor had enough variability to detect a low & high level, allowing for hysteresis.  A bigger reservoir with more room for overflow & longer wires would get better results from a 2 wire sensor but cost more.

    The automated power button & level sensor were good enough to finally design a 3 transducer unit.

    An unfortunate discovery was raising the gatorade bottle by just a little or putting too much water in was enough to cause the water to siphon out & flood out of the sprayer.  It might actually be more effective to have a solenoid valve instead of a pump & gravity feed it.

    These things arrived.  They all worked, contrary to reviews.  This model doesn't time out & doesn't detect running dry, but they don't seem to burn out.

    Through hole soldering is still essential for an experimental design like this.

    It worked, with all the misters being managed automatically.

    Current draw overheated the voltage regulator after a few hours.

    The cable management is a mess.

    The only reason for keeping all 3 boards was to detect being out of water, but now that some models don't detect being out of water, it might be worth making a custom board to drive all 3 with 2 wires.

  • Custom enclosures

    lion mclionhead07/09/2021 at 05:00 0 comments

    So the stock enclosure leaks when fed by a pipe, so a custom enclosure was needed.  There are some pretty good commercial humidifiers which do the job for very little money.

    Of course, there's no mention of whether they use a MEMS atomizer or a boiler.  Ultrasonic, cool, & incompatible with essential oils are good indications of MEMS.  With all the problems, it's almost not worth trying to duplicate a humidifier from scratch & probably going to cost more.  They all use a gravity fed water tank.  The outlet always points up.

    There's not really enough room on the table to put a humidifier with much of a water tank anywhere.  A pump made out of a hobby motor was to separate the water tank from the transducer, but it's really complex with a 2nd voltage & electronicals.

    With the transducer removed from the stock enclosure, it was possible to document the inlet facing side.

    100mm Macro




    The lion kingdom's microscope game could be a lot better.  It's still a webcam because it's hardly ever used.  The holes were not visible from the outside at any magnification.  There's no simplified explanation of how MEMS atomizers work, only a few chinese research papers.  It appears to be just a titanium plate with holes etched in it.  The smooth metal is where a photoresist once was.  The acid created a rough surface around each hole.

    The titanium plate vibrates rapidly.  There's a film of water on the outside.  According to kiwipedia, the vibration creates capillary waves on the outside.  The capillary waves become too tall to support themselves & tiny drops fall off the tip of each wave.  

    There's no slow motion footage of a MEMS atomizer.  It's not obvious why the mesh has to be a dome other than to show the user where the water comes out or to strengthen it.

    After observing cracks forming on the outside, the mode of failure is believed to be work hardening of the metal over many hours of vibration.  Eventually, it just cracks.

    Custom enclosure #1 had a lot of leaks.  The printer can't print smooth surfaces so the transducer couldn't make a water tight seal.  The screw holes leaked.   Facing up was definitely the best way to point it.

    The best way to seal the screw holes was just to add glue where the water could leak out.  Adding silicone grease under the transducer made a water tight seal against the uneven printing.

    It worked for a few seconds after refilling the tank, then died until the tank was drained & refilled again.  It was believed to be forming air bubbles under the transducer.  Instead of floating up in the original side firing arrangement, they stayed in place until it died.  

    The vertical firing products obviously have more going on to feed the transducer than just dunking it.

    Enclosure #2 solved the air bubble problem.

    A new ESC didn't beep when the motor was off.  Castles beep.  Turnigies don't.  This one required 7V.

    The best way to detect water level was just measuring resistance.

    Atomizing with the automatic water pump worked.  

    The next problems were manely with the water sensor.  It needs 2 sensors to give it hysteresis.  Otherwise, it constantly spins in stall mode while the ESC gets hotter & hotter.  

    The sensor needs to be securely farstened.  If it falls off, it'll pump the entire gatorade bottle on the floor.

    5V needs to come from the ESC so everything has 1 power source.  

    It needs a way to arm the water pump.  The ESC has to detect idle speed when it comes on.  If the ESC is turned off while the transducer is moving water out, there's no way to turn the ESC back on without turning off the transducer.

    All the electronicals  & the transducer should be self contained.


    Read more »

  • Water level sensing

    lion mclionhead07/08/2021 at 08:58 0 comments

    Well, it needs a tall tank so the pump's side flow doesn't splash everywhere.  Some fine tuning is required to get just enough pressure for a certain voltage without too much side flow.  Once tuned, the PWM value could be hard coded.  An ESC which doesn't constantly beep is required.

    The hose fitting for the stock reservoir had the hose stop outside the reservoir, so the water went sideways instead of in the reservoir.  It needs to go all the way into the reservoir to keep water from going sideways.

    The stock reservoir was no longer water tight after drilling out the hose attachment.  The original reservoir manetaned a vacuum which kept water in.  

     Without a water level sensor, the pump has to be manually  toggled.  Sensing water level would require a pretty complicated sensor.  The stock tank is too small for any conventional sensor to fit.  A conventional sensor would displace all the water.  The leading theory is to have a custom ultrasonic sensor measure the resonant frequency of the tank.

    It is believed the reservoir is as small as it is because the MEMS transducer leaks if any more pressure is applied.  You couldn't attach a bigger tank & call it a day.  A bigger tank could gravity feed into a smaller tank.  

    The MEMS atomizer requires 2 tanks, 2 circuit boards, 2 voltages, lots of wiring to the pump & the atomizer, a sensor to manage the water level.   The atomizer & all the plumbing take a lot of space & have a lot of problems, which got the lion kingdom thinking of alternatives.  The leading alternative is an automotive fuel pump

    feeding a common mister,0-0197/dp/B08T17V72R

    to atomize the water.  It would require only 1 water tank & 1 pump.  A test with a .2mm printer nozzle showed the printer nozzle with home made pump just squirted.  It may require a lot more pressure to make a mist.  That's why the safest bet is an automotive fuel injector with automotive fuel pump.  They're just expensive.

  • Designing a pump

    lion mclionhead07/05/2021 at 23:00 0 comments

    The cheap pumps on the internet have sketchy reliability & are not self priming.  They need animal power to get started, which makes topping off a tank a pain.

    The home made pumps are not waterproof enough to last very long.  Any submerged bearings or brushes would die quickly & contaminate the fluid with oil.  All motors end up rusting & dying, including the commercial pumps.

    The ideal pump would be a peristalsis pump.  The complete pump is over $25  The flexible, high endurance tube alone is a more tame $3.50.

    What lions needed was a submersible pump which would last a long time in pulsed mode.

    The lion kingdom went all the way to designing a simple reciprocating thing with a custom check valve & a solenoid driving a plunger.  

    The idea was the plunger would have enough drag to develop pressure without a seal.  This was a failure.  The valve couldn't keep the water out & a plunger without any seal couldn't develop any pressure.  It might be more practical if the plunger was in a rail gun which accelerated it to high velocity & the valve had a spring loaded diaphragm.

    The internet is all over the place regarding lifespan of submerged motors & the lion kingdom has a large inventory of small brushless outrunners, so the decision was made to try submerging one & see what happens.  

    It actually pumped some water through the tube, while burning .5A 6V.  The seal around the motor was lousy.  As an outrunner, it needed a gap around the motor which water was more inclined to flow through than the tube.  An inrunner could block flow around the motor, but they're a lot scarcer & more expensive.

    The water picked up a lot of oil from the motor.  It was surprising just how easy it was to make a pump from a brushless motor.

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