Hello and happy Christmas all.

I find electronics very interesting but I have never dipped my feet in this area so any guidance for my Christmas project would be appreciated.
I have ordered a 1.7mhz ultrasonic transducer fog machine off ebay and I'm waiting for it to drop on the door step.

I would like to know how such a circuit works. I understand how the piezo transducer atomises and that for it to do so the circuit must pulse a 1.7mhz sine wave to the transducer. Firstly I'm wondering how this is done, at a guess I imagine some sort of capacitor set up is used to charge and discharge at the correct rate?

What i'm going to have a go at is building my own PCB or breadboard that runs off a 5Vdc Li battery I have. (I dont want it plugged into the wall).
Once a button is pressed the fog starts - more fog the better! I want to make the design as simple and cheap as possible.

If anyone has an idea of how I could design such a circuit please help a noob out!

Thanks
Alex

 

The piezo disk is usually driven by a high powered oscillator, some of the circuits use the disk as their frequency determining element. It is important to drive the disk at it's resonant frequency, for best performance. There are published circuits but I don't have links to them. One thing that is going to be a problem for you is that those are high impedance devices, and that generating a fog-mist takes power, and at 5 volts you will not be able to deliver enough current to have much power. And I am not aware of any way around that because it is rather fundamental physics. You are going to need more voltage to provide enough power.

 

Hello Alex.My name is Gabriel and Merry Christmas to you as well.

I find electronics very interesting but I have never dipped my feet in this area so any guidance for my Christmas project would be appreciated

let us see if your fog machine works. first of all. then perhaps we can tackle the questions you have only because you will have a working example, very good reference to start with. Then your goals and ambitions will fall in line quite nicely....I hope.

 

Thank you both!

Gabriel, I will share the circuit with you as soon as I can. I agree this would be a great starting point for the project.

Bill, the power issue you have raised is a very interesting one. Forgive my lack of knowledge here but is it possible to 'step up' the voltage of a 5v battery using a transformer or such, would this provide the power required?

Failing that I may have to think about a more energy efficient means of creating the right level of resonance.

Thanks
Alex

 

What are you using as a "5V battery"? That's an unusual voltage for a battery, although it is commonly used in power supplies.
I think you're going to need a several tens of volts to power a fog generator to your liking.

 

I once created an oscillator driver circuit for a piezo sounder using a hex schmidt inverter IC. one inverter as an oscillator and then one more inverter to drive the last sets of two inverters to feed opposite sides of the piezo with opposite polarities. It may also work with a CD4049 IC, but setting the frequency will take some experimenting. The inverter oscillator has a capacitor to common at the inverter input and a feedback resistor from that gate's output back to the input with the capacitor. The inverter needs to have some difference between the high to low switch voltage and the low to high switch voltage. A schmidt inverter certainly does, others may work. And it does need to be a CMOS IC.

I hope that somebody is able to draw the circuit, presently I lack a cad program on a working computer.

 

Thanks all.

Alec, I have double checked the battery I have and it is actually 3.7v 2200mah. That probably makes my project even harder I suppose?

Bill, looks like you've had some success with a similar design. Do you think it would be possible for this to work on 3.7v?

Would anyone be kind enough to help draw this for me, even if it is very rough on paper? I will then have a go at building and testing.

Many thanks
Alex

 

That probably makes my project even harder I suppose?

The typical fog/smoke machine uses power in excess of 500W. That's way beyond what a single 3.7V cell can provide.

 

There are commercial ultrasonic fogger circuits available on Amazon. Even ones that run on as little as 3.7V. Perhaps studying one of these will help you. Click on the embedded link

 

The units in that link get rather mixed reviews, and it seems more than 3.7V is needed in practice.