Please take into account I'm a beginner with microelectronics.

I want to build an automated air humidifier.

For this, I'm using a STM32 blue pill and a si7021 I2C sensor. The I2C sensor regularly measures the temperature and humidity in the room. That's the part of my project that properly works at the moment.

Depending on the humidity level in the room, I'd like to trigger an ultrasonic water atomizer. I bought a pack of atomizers here: https://www.amazon.fr/gp/product/B07F3YY6K7

From what I could find, these atomizers should be powered by a DC 24V current, which is obviously way more than what the blue pill can provide on its own.

That's where my knowledge ends. I don't know how to power and control these atomizers. What's coming is no more than an educated guess.

I imagine I need to get a 220V AC mains to 24V DC adapter. This 24V current then needs to be split:

  • to 5V to power the board, and maybe other components (like a bluetooth chip)
  • to 24V to directly power the atomizers

But once all the components are powered, the blue pill needs to be able to enable/disable the power to the atomizers.

So what I'm missing is (I guess):

  • a way to convert 24V to 5V
  • a way to control the power to the atomizers from the blue pill

Can you point me in the right direction please?

  • 2
    \$\begingroup\$ Those disks are just transducers, you need some driver to make those "ring", you can't do it with 24V dc alone. \$\endgroup\$
    – Vlad
    Nov 10, 2019 at 15:54
  • \$\begingroup\$ By "ring", you mean applying current with a certain frequency? Like HIGH-LOW-HIGH... at a certain frequency? If I get a device that can control the HIGH-LOW state to the transducer, I can control the frequency from the MCU right? \$\endgroup\$
    – JPFrancoia
    Nov 10, 2019 at 16:21
  • \$\begingroup\$ For a beginner in "everything" on this topic, including "learn how to learn what you need to know" Ask yourself what are the key words to find some answers and then also consider, how to I avoid making an incubator for deadly bacteria, and fungus in the air? ..I would use google images and use words like "ultrasonic driver schematic" then drill down to source and read. You have a lot to learn about power conversion, drivers, sensors and control systems \$\endgroup\$ Nov 10, 2019 at 16:32
  • 1
    \$\begingroup\$ the uC adds no value to the atomizer/nebulizer, it is only your choice to make an intelligent user interface which is TBD. A control signal does not need a uC from a sensor to enable power to driver \$\endgroup\$ Nov 10, 2019 at 16:41
  • 1
    \$\begingroup\$ With your Chemistry background, and interest in control systems in Pharma, I might research how C60 (carbon Fullerene) will be used in target delivery of pharmaceuticals and cancer treatment in the next decade or 2. \$\endgroup\$ Nov 10, 2019 at 17:19

1 Answer 1


You are heading in the right direction; let’s suppose you get a 24V power supply with can supply enough current to the atomizers.

The most efficient is to use a Buck DC-DC converter module to transform the 24V -> 5V with an efficiency of about 90%. Alternatively you could use a linear regulator, but it will dissipate a lot of power depending on how much current you need at 5V.

To turn on the atomizer you could either use a relay (driven by a little transistor connected to the MCU) or a MOSFET rated to carry the current of the atomizers.

Edit: as mentioned by Vlad, the atomizers listed are just transducers. So they need to be driven at the correct frequency - not just a DC voltage. For this MOSFETs are more suitable than a relay.

  • \$\begingroup\$ Ok thanks for the Buck DC-DC. Why is the MOFSET more adapted than the relay in this case? How do I dimension the MOFSET for this use case? \$\endgroup\$
    – JPFrancoia
    Nov 10, 2019 at 16:23
  • \$\begingroup\$ Ok, it seems making the trasnducer driver will be a lot of trouble at this stage, so I bought this instead: bestmodulescorp.com/bmz00040.html. Now I just need to handle the power supply. Thanks for your help. \$\endgroup\$
    – JPFrancoia
    Nov 10, 2019 at 19:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.