Replacing a Failed 113 kHz Piezo Mist Driver

[James Anderson]

I bought a small desktop evaporative cooler that uses two piezo atomizers to generate mist. It worked surprisingly well, but the hard water here quickly caused the atomizers to clog.

After cleaning them several times, the original controller eventually failed. I found a burned R4 on the control board, so instead of replacing the whole unit, I decided to build my own piezo driver.

The replacement atomizers I bought have a resonant frequency of about 113 kHz, so I designed a simple oscillator and MOSFET driver around that target frequency. I initially tried one design, but it failed. The second version was tested on a breadboard and successfully produced a frequency very close to 113 kHz, with considerably stronger mist output than the original unit.

I used BC337 transistors for the oscillator. Interestingly, the batch I bought had surprisingly large β variations, so I measured them and selected a matched pair.

One remaining problem is the frequency counter. Connecting it changes the atomizer behavior, suggesting that the counter input is loading the oscillator. I may need to redesign the input buffer.

The final circuit was built on perfboard using component leads as point-to-point wiring.

Has anyone here worked with ~113 kHz piezo atomizer drivers? I'm particularly interested in suggestions for improving the oscillator stability and measuring the frequency without affecting the piezo driver.

I'd also be interested in hearing about other simple approaches to driving these resonant piezo elements.



 

[Doctorandus_P]

I've heard of areas around these mist drivers to turn white. The small water droplets evaporate, but the chalk does not and thus falls back to the earth. It's best to use demineralized (No mr. spelling foulup, it's not decriminalized) water with these things.

For non invasive frequency measurement you can use a "near field probe". The "western" versions of these are horribly expensive (few hundred EUR), but they are actually very simple devices you can DIY yourself, or get a EUR 20 set from china direct.

[Manul]

I've heard of areas around these mist drivers to turn white. The small water droplets evaporate, but the chalk does not and thus falls back to the earth. It's best to use demineralized (No mr. spelling foulup, it's not decriminalized) water with these things.

One more reason is health. Cold mist humidifiers are poluting the air with lots of hard particulates and is bad for lungs. Demineralized water is highly recommended.

[Analog Kid]

I bought a small desktop evaporative cooler that uses two piezo atomizers to generate mist. It worked surprisingly well, but the hard water here quickly caused the atomizers to clog.

After cleaning them several times, the original controller eventually failed. I found a burned R4 on the control board, so instead of replacing the whole unit, I decided to build my own piezo driver.

[...]

Question:

Who the fuck are you, and why did you copy my posting?

I expect an explanation from you, pronto.

[EEVblog]

Who the fuck are you, and why did you copy my posting?
I expect an explanation from you, pronto.

Looks like he replied to your previous thread and decided to build his own? 

[Analog Kid]

Who the fuck are you, and why did you copy my posting?
I expect an explanation from you, pronto.

Looks like he replied to your previous thread and decided to build his own? 

I guess.

I did see that he replied to my post in that thread.
But here he seems to just be paraphrasing what I wrote there, in the first person as if he did what I did.

Remarkable that he decided on the same circuit design, used the same transistors (BC337), had a bad batch of them, used perfboard, etc., etc. Quite a coincidence, dontcha think?

Whatever. No action needed on the part of mods; it just pissed me off is all.

[squadchannel]

I bought a small desktop evaporative cooler that uses two piezo atomizers to generate mist. It worked surprisingly well, but the hard water here quickly caused the atomizers to clog.

After cleaning them several times, the original controller eventually failed. I found a burned R4 on the control board, so instead of replacing the whole unit, I decided to build my own piezo driver.

[...]

Question:

Who the fuck are you, and why did you copy my posting?

I expect an explanation from you, pronto.

James Anderson, you're reincarnated @xecor and @meoly (banned both)
same Koto City(Koto-ku) guy.
reported.