I recently purchased this atomizer module from AliExpress. It works as one might expect when I plug it into a power source, and place the piezo disc on a film of liquid.
However, it comes with its own power switch that needs to be turned on each time because (I guess) it's a normally open switch. Rather than design my own circuit (and I have serious questions about my ability to do that!), it seems it should be simpler to short the contacts for the switch. However, I am unsure whether it matters which of the contact points need to be bridged - there seem to be 4 soldered points. The attached image shows the front and back of the module.
lanewsa:
However, I am unsure whether it matters which of the contact points need to be bridged - there seem to be 4 soldered points.
The switch has two pins that are the actual switch mechanism, and two more that are a metal frame to help hold the switch steady when you press it.
Just looking at the tracking on the solder side of the PCB it should be obvious that one of the switch contacts, and both of the frame pins are connected to the same point, which also connects to the outer contact of barrel power connector.
If you cannot see that for yourself, then I seriously doubt whether you have sufficient electronics knowledge / experience to be modifying the circuit.
It looks like a momentary push to make switch and there is probably a latching circuit so the function is likely to be toggle on / toggle off.
You bridge the upper two connections on that switch to simulate a push of the button.
If you are intending to control the device from an Arduino, then a relay module is the easiest solution but there could be other and better options.
@RailRoader: Haven't received any responses from AliExpress
@TomGeorge: My experience with the switch is that once pressed/released, the piezo continues to emit mist until the switch is pressed again
@JohnLincoln: My inexperience with electronics is precisely why I was asking for guidance; while some things are obvioius to experts, clearly they are not to me
@6v6gt: Yes, my intent is to use an Arduino. I thought of using a relay module, but the switch is still going to be an issue, as I need to bypass it
@wvmarle: The switch appears to latch open or shut on each press, so tape wouldn't work.
Yes, but you have described it as a toggle and it seems it is only intended to be "pressed" briefly.
Anyway, try it - short the two switch pins and see if it turns on and stays on when you power it up. If it does not, you will need some Arduino "intelligence".
Actually, it is even easier to find this out. Just hold the switch - and keep it held - before you power it up and see if it starts and continues to operate indefinitely as you keep the switch held.
If it does not behave in the way you want, you need to measure the voltage across the switch with a DMM so we then know how to interface it.
Either way, at some point in time I will need some Arduino intelligence, either through a relay module or something (what something, I am not qualified to say; at least I know that a relay module will work).
Hi @Paul__B: I can report that your suggestion (pressing and holding the switch before applying power) worked as you thought. The piezo disc emits mist until I remove power. That (to my noob brain( suggests that shorting the switch connectors should do the trick.
My next test will be using a relay module from the Arduino to this mister module. Since I've used relay modules in the past with an Arduino, I expect this should be straightforward.
It does suggest to me that there should be a way to replace the relay module with a MOSFET, so power can be delivered through the Arduino to the mister module? Am I thinking about this the right way, or am I off-base?
For power delivery: an Arduino is NOT a power supply. You will need some form of external power supply, which of course in turn may also be able to power the Arduino. It seems that mister can run off 5V, that's perfect for powering the Arduino as well.
You can probably use a MOSFET to switch the power to the mister. Switch low side, using a logic level n-channel MOSFET.
Firstly, since this gadget already has a power switch built in, why do you need to switch the power separately? You could simply interface the Arduino to the pushbutton to turn it on and off. I foresee a slight concern as it is a toggle function, knowing in which state it has "landed", however there are ways to determine this.
@wvmarle: you're right! Duct tape across the switch is a less-destructive solution (I mean, I preserve the original circuitry), and yes, the power I'm currently applying is 6V (power supply limitation).
@Paul___B: A relay is the easiest for me to deal with conceptually, but you're correct - ideally I'd like to learn enough about electronic circuitry to not use a relay. Alas, I don't quite know how to do that (yet!).
Only one advice ... first, test if that circuit have a protection routine ...
Some of these atomizers uses a feedback from the driver circuit (change in the signal or current, not remember now) for "sense" if there is water or not in contact with the piezo disk, and if there is no water they switch off the circuit after a pair of seconds for prevent piezo damage ...
Usually are the ones with piezo disc submersed, but i'm not sure if also the ones with the "wet pads" in contact with the disk do the same ... if yes, making the piezo work continuously without water can burn it ...
lanewsa:
A relay is the easiest for me to deal with conceptually, but you're correct - ideally I'd like to learn enough about electronic circuitry to not use a relay. Alas, I don't quite know how to do that (yet!).
Just use the module I cited. It works virtually the same as a relay.
Did I not mention? How about a Web link to the module you are using? I couldn't find it as such.
@Etemenanki: Good point. I do plan on adding a liquid level sensor at some point in time, and that should ensure that the piezo is not triggered at an inopportune moment.
lanewsa:
... I do plan on adding a liquid level sensor ...
Then you can probably use a small N-channel logic-level mosfet instead of a relay , if you want to drive it from Arduino ...
i mean, correct me if i'm wrong, but looking at the image you posted (PCB) seem that this button close the pin 4 of the chip that drive the mosfet to ground, with no pullup resitors (this make me think that is some sort of mini-MCU like attiny or similar with an input with pullup internally activated, but here i'm just guessing cause there's no part number on it) ...
so a small logic-level mosfet, also one in TO92 case, like as example ZVN2106A and similar ones, can be used for close the button drived from arduino, that can also check for the presence of the water ...
Just hold the switch - and keep it held - before you power it up and see if it starts and continues to operate indefinitely as you keep the switch held.
