Mist MAker Via Oscilloscope???

[InFLak]

Hi,
I bougt a mist maker. Than i open the piezo on top. I saw a ring, which is connected to piezo. Piezo is connected between body and this ring. THen i connect this ring and body to oscilloscope. On the box of mist maker , it is writed that it works at 1.7Mhz.

i Put wet paper between water sensor and body, it lights on ,(it has lights which on while working.) Bu t i shocked! Osc. shows about
370.4 Hz, and it is like sinus wave , but not a exact sinus, it is like triangle. Then i push wet paper. The amplitude increases but frequency not changes. The vave form changes to sinus wave.

1 week ago i open a broken mist maker. There was only one driving transistor: BU406. But i cannot able to look properly the circuit. Becaouse they protect circuit with cement like thing.

I wonder piezo changes the frequency? Do you know how can we drive this transduver? How. If not why it was 370.4Hz?

Can youhelp me?

 

[audioguru2]

InFLak,
Do you want to fix the broken mister by making your own circuit to replace its "cement thing"?
The piezo certainly doesn't work at 1.7MHz, so the cement probably has a digital frequency divider inside. The little piezo will have a very low efficiency at only 340Hz, and its buzz would be annoying, so please check again its frequency on your working unit. The frequency is probably 25KHz to 45KHz. The BU406 is just a high-voltage output amplifier.

 

[MP1]

Inflak, without seeing the circuit it is hard to tell, but your scope might be interfering with the circuit, too. Since you have two units, it is best to rely on a comparison between the two rather than actual voltages and frequesncies.

MP

 

[InFLak]

Yes audioguru i want to make my own mister(Mr,not miss )

But it is period still 2.7ms(=370Hz)


Bu406 drives the transducer. But output is AC sinus wave?

There was some connections to body inside mister. Do you think

they provides AC current?

 

[InFLak]

Do You think this is possible:

The piezo have a capacitance. A inductor connected (parallel) to piezo.

In every period, circuit goes damping as an LC lircuit.And its

frequency is 1.7mhz.

So, while circuits frequency not 1.7mhz, piezo works at 1.7 mhz. In every period, Piezo charged energy then goes damping.

Is it right???

 

[audioguru2]

InFLak,
You are correct that 2.7ms is 370Hz. Perhaps the ultrasonic vibrations are produced in bursts, with a burst-rate of 370Hz. The time of the pause between bursts will allow the water to re-coat the piezo.
As you say, maybe the piezo resonates like an LC circuit at a very high frequency. It may not need an inductor across it since a piezo resonates strongly by itself, and even more if a tuned acoustical cavity is behind it.
So in every period of the 370Hz, the piezo self-resonates at a very high frequency for half the period.
You are right!

 

[InFLak]

I have max038,

I think i will make a waveform generator after my final exams.and drive my piezo

But how can i drive piezo.

Do you think Bu406 works?

Or am i have to drive with power H-Bridge?

 

[audioguru2]

InFLak,
The piezo doesn't need triangle or sine-wave drive, a 555 or CMOS oscillator can drive the BU406 transistor. You don't need an H-bridge. Just copy the output wiring of the original.
If the BU406 is bad then replace it with a good one.

 

[InFLak]

The opened bottom of ist maker...

View attachment 35421

 

[InFLak]

And its citcuit in cement (or like thing)

View attachment 35422

 

[InFLak]

there is a problem i think.