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[on:]

Hi everyone!

I'd like to build my own ultrasonic fogger/atomizer. I've been looking at a module on the internet http://www.alibaba.com/product-gs/213577479/High_Efficiency_Ultrasonic_Atomizer_Transducer_for.html but then I do not know how it works (I'm assuming it works like a speaker, except at much higher frequency), and also I do not know if an arduino can make it work.

I think that I need to increase it to a 2-3MHZ frequency at 12 volts for the atomizer to work, but then how can I do this with an arduino? Can I use PWM to make it happen? Can an arduino do PWM at 3 MHZ?

Please share with me your ideas. Thanks so much!

A

[Reply #1 on:]

Can an arduino do PWM at 3 MHZ?

No...  The default PWM frequency is ~500Hz.  And, you probably don't want PWM anyway.

I assume the thing runs off a square wave, and there are easier ways to generate a square wave.  I'm not sure if an LM555 can go to 2MHz, but I'm sure there are oscillator/multivibrator chips that can.   You'd also need to boost the power with a MOSFET or something.   

You can also buy a complete fogger/mister with the oscillator built-in.  One nice thing about these (besides being built and ready to go) is that the oscillator & electronics are already enclosed in metal so you aren't "broadcasting" high-power RF signals.   I've got one of these things...  I forget the power rating... probably medium power... I paid less than $100 USD for it....   I tried it out in the bath tub and it generated enough fog that you couldn't see the water, but not enough to fog-up the bathroom...   Dissapointing...   I think the droplet size is large compared to a regular fog machine and I'm guessing it falls to the ground before it can be spread-around.

[Reply #2 on:]

You can generate much faster frequencies with pwm but you end up losing resolution by decreasing the bits/top value...

Normally the atomizer transducers use a self resonant circuit to maximize power transfer.
A Google image search for "ultrasonic atomizing circuit" gives lots of examples like this one:
http://www.seekic.com/circuit_diagram/Basic_Circuit/Medical_ultrasonic_atomizer_1.html

A few years back I experimented with a 200w ultrasonic traducer, I used phase angle to track the resonant frequency:
http://krazatchu.ca/2008/04/17/ultrasonic-resonant-tracker/

[Reply #3 on:]

I Worked on medical ultrasound devices in the 60's and I need to point out that the transducer then was a Quartz Crystal about 25 mm across and 6 - 8 mm thick. Those devices worked at about 80 to 120 khz (some were tunable (a power VFO or transmitter connected to a resonant load, the Crystal) and were part of a power oscillator that made between 20 and 50 watts power delivered to the Crystal. Not a device that could be powered by an Uno but certainly controlled, sensed and turned off or on by the Microcontroller. Do be careful as RF power at any frequency is Very Dangerous as it COOKS flesh MUCH FASTER and DEEPER than MAINS POWER CAN. Mains power will cause muscular problems and is very bad for the heart and brain but not the burns that RF power can. Direct Contact with any active wiring to a transducer is very dangerous. Newer Ultrasound devices work at higher frequencies and RF penetration depth on human skin/flesh is worse and more dangerous as the frequency goes up. I once came in contact with the RF out from a 100 watt 150 mhz transmitter and the burn was cone shaped internally (the end of my finger) and took about 8 months to completely heal.

Doc