Tuned LCR circuit for humidifier

Hi,

I have a humidifier circuit board which I wish to adapt for use for use at a different frequency. Currently the circuit operates at 1.6MHz and I wish it to operate at 100KHz. The atomiser, which is mechanical and essentially bubbles off the water, has an equivalent circuit which is LCR in series with a shunt/static capacitance in parallel. So to 'neutralise' this affect and ensure power is delivered correctly the accepted practise is to shunt the atomiser with an inductance either in series or parallel.

Now the resonant frequency (1.66MHz) is determined by F=1/(2Π√(LC)). So I should be able to replace either L or C with a variable component and essentially tune the frequency down to 100KHz.

My question is this - which component do you think it would be best to replace?

I've done some electronics in the past but I wouldn't describe myself as skilled in this field.

I have mapped the circuit board in a picture at the link below. A+ and A- represent the atomiser. There are two inductors, one is marked up like its a resistor at 100ohms. It is an inductor at 100µH (my mistake). There are quite a few capacitors, of those I wouldn't know which was best to replace.

Thanks. I'll reply promptly to thoughts and I hope it's not too difficult a question.

I would have thought the frequency is probably set by the atomiser itself?, usually a piezo element of some kind - and wouldn't imagine it would work at a different frequency. Why would you want to try and change it anyway?.

Hi Nigel,

Yes the atomiser does have a piezo element. Currently the atomiser resonates at 1.6MHz and the circuit works at 1.6MHz. I'll be changing the atomiser to a different one that resonates at 100KHz so I need the circuit adapted to work at 100KHz also. It is for use in an air freshener.

Thanks,

Antknee.

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Antknee, your circuit does not make any sense, I suggest that there are numerous errors in there.

As Nigel commented, I would expect that the atomiser element is designed to work at a fixed frequency, in this case 1.6Mhz.
Trying to operate it at 100khz sounds like a poor idea, why do you want to do this?

JimB

The piezoelectric transducer has a mechanical resonance at 1.6 MHz. Driving it with a different frequency will probably accomplish nothing, even if the circuit is resonant at the new frequency.

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Would be a lot easier to validate the schematic if it had the component designators on it. The B C E notatons for the transistor leads would be especially helpful. While you're at it, please mark the blue and yellow transducer wires. (Where is the transducer on your schematic?)

Also, post a data sheet for the new 100kHz transducer so we know the impedance that you're matching to.

Antknee,

How many are you making? You might want to redesign the board. 100Khz is not hard to get.

What was wrong with the 1.6Mhz piezo?

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Google "lm555 timer" or "555 timer online calculator". I think they can run at 100KHz. You will need to rectify the and drop the voltage as well and then use pin 3 to drive the driver on the piezo board.

Hi mramos,

I have a 555 timer which I'd thought of using but didn't know how! I did google it. I need the atomiser to be at 36V AC although the current can drop. I'm not exactly sure what you meant by "to drive the driver on the piezo board". Or how to do that.

Cheers,

Antknee

It looks like I'll have to print your schematic and add my own component designators (R, C, Q, etc). Then I can trace the board and try to understand the circuit and how to modify it. Maybe in a day or two....

A few problems......

The capacitor in series with the yellow wire CANNOT be 0.1pF.
Is the capacitor from the collector of Q4 to ground (green disc) really 10uF?
The capacitor from the big transistor C to V+ is electrolytic. Recheck, it isn't 600pF.
There are terminals labeled "SW". Is it a switch? What does it do, if anything?
What does the rheostat "VR" control? Power or frequency?
I can read the markings on the big transistor, I need the markings on Q3 and Q4.
What are the R designators of the:
2.2K near R11 (it might be R12)
2.2K near C1
1K near L2
The C designators andmarkings on:
Black tube near R15
Green disc near Q4
Orange drop near L2
Burgundy drop next to the blue wire
What are the markings on C6?

I'll bet that the round device next to C6 and R15 is an inductor! It's 600pF on your schematic. It's probably in fact 60uH.

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I've taken a pick of Q6 the capacitor in series with the yellow wire, it says .1K

Click to expand...

Please explain. I do not find a device named Q6 in series with the yellow wire. All that I can see is a capacitor. It is 0.1uF, and appears to be C4.

L1 on your schematic is still a 600pF capacitor.

The photo of C6 is the unmarked side. What are the markings?

What are the markings on the face of Q2?

What are the markings on the face of Q3?

Please, attention to detail is important.

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My mistake, I don't know why I wrote Q2.

That's cool.