How to make a DIY ultrasonic humidifier

Recommendation points

• Difference from a steam generator
• Body parts
• Ultrasonic evaporator
• Dry run protection
• Power and automation
• Final assembly of the device

Dry air in living quarters is an absolute of discomfort and one of the root causes of poor health. But you should not rush to buy expensive equipment if you have the time and resources to make the simplest humidifier yourself, moreover, as a highly efficient compact device.

Difference from a steam generator

Household humidifiers are of two types. Some work by increasing the evaporation area, others by heating the liquid to form steam. In both cases, the evaporation of water occurs naturally, we will not talk about steam generators today..

Most modern household appliances use a piezo emitter – a plate vibrating at an ultrasonic frequency. The principle of evaporation is as follows: water breaks down into very small particles, a finely dispersed suspension, which cannot “stick” back together and continue to exist in the form of water vapor. The advantage of dispersed humidifiers is low energy consumption and almost complete absence of scale in the device itself, which affects its durability.

Household Ultrasonic Air Humidifier

Body parts

We recommend using an airtight food container as the housing for the humidifier. Its height should be at least 150 mm, and its width should be about 300 mm.

The water tank is an ordinary three-liter can. It will evaporate completely in 6-8 hours, if you need more, use five-liter bottles or cylinders for drinking water.

There are two types of connection between the container and the body. In our case, we will be installing the can upside down on a round wood washer. Of course, the service life of such a part is not too long, but nothing prevents the manufacture of a new one. In addition, you can take a “moisture resistant” tree as a basis, for example, larch or linden. First, we drill a washer from a board 50 mm thick with a 100 mm wood crown. Then, using the existing hole in the center with a 75 or 80 mm crown, we make an annular groove with a depth of about 15 mm, and then select the central part with a 60 or 50 mm crown.

Using a pocket knife, we expand the sample from the crown to 9–10 mm, then we pass it inside with a thin chisel, giving the correct profile. As a result, the washer should fit snugly on the jar, like a lid. On the upper edge of the washer, we make a cross-cut cut with a hacksaw to a depth of about 15 mm so that small holes are obtained for air intake and water outflow. As a result, the structure should work as a drinker for young poultry..

As a second option, you can use an external container: a small tank or canister connected to the evaporator by two thin silicone tubes. It is important, however, that the supply tube exits at the very bottom of the container. The cut-in level of the second hose precisely determines the height of the water layer.

Ultrasonic evaporator

This is, in fact, the only expensive part that you have to buy. But do not rush to purchase components for existing models of air humidifiers, they are at least twice as expensive.

An ordinary piezoelectric element costs from 300 to 500 rubles. You can buy one at online auctions, or directly from China. Make no mistake in your choice: a “bare” piezoelectric element will not work, you need a device in a waterproof case with a pair of outgoing wires and a plug at the end. The difference is that such a humidifier has all the necessary piping to generate the required frequency and can be placed literally in any container with water without additional waterproofing.

The evaporator must be fixed to the bottom of the container in an arbitrary place, but not close to the walls, leaving free space for installing a container with water. If the evaporator body is not waterproof, or the plate does not sink deep enough during installation, the unit can be fixed to the bottom of the container from the outside. It is necessary to make a neat hole for the edge of the plate and seal the junction with sanitary silicone. For stability, the container will need to be equipped with legs or a stand.

Dry run protection

The emitter must always be immersed; this is critical. Without water, it resonates, heats up and breaks down in seconds.

Dry running protection can be performed with a simple washer fluid level sensor for domestic cars. It is advisable to purchase short float sensors with a reed switch in a small tube, otherwise there is a high risk that the humidifier will turn off before the water in the bank runs out.

Place the sensor on the bottom of the container so that after placing the can it is inside. If the container is installed separately, the sensor is installed in it. The normal operating mode of the sensor is an open contact, but there can be several switching circuits. To invert the signal, use an intermediate relay or semiconductor switch. If the contact sensor has a standard operation scheme, then it can be connected directly to the open circuit of the power supply of a low-power emitter.

Power and automation

Most piezo emitters are designed for low voltage power supply of 12 or 24 VDC. There are tons of options for how to power a homemade humidifier. We recommend, solely for safety reasons, to place the power supply and automation unit in a separate case..

The simplest and most versatile option is a PC power supply. They have a unified designation system:

• yellow wires +12 V;
• black wire – common minus;
• dark blue wire – 12V in reverse polarity (up to 0.5A).

Thus, a 12 V connection is made with a black and yellow wire, and a 24 V connection is made with a yellow and blue one..

Since a perfectly stabilized voltage is not required to power the emitter, you can use small transformers from old radio receivers and other household appliances with a diode bridge and without a frequency generator. You can wind the transformer yourself on a small (up to 30 mm) ferrite core, since the power of the piezo emitter is minimal.

To automate the operation of the evaporator to turn off when a certain level of humidity is reached, it will be necessary to assemble a small circuit by hanging installation. The first part is a DHT11 sensor with a digital output signal. The second element is the Arduino mini as a digital controller. The operating device of the circuit is a thyristor switch or micro-relay with a consumption current of up to 0.3 A, and a variable resistor of 10-15 kOhm acts as a regulator.

1. Power connectors. 2. Key transistors. 3. Arduino controller board. 4. Moisture sensor

The sketch (algorithm, firmware) for such an assembly is very simple. We declare two global int variables and write in them the values ​​on the Pins of the sensor and potentiometer. To compare the values, only one if-else construct is used in an infinite loop, the secondary condition of which is an exception that turns off the piezo emitter relay if the value of the variable humidity exceeds the setting value. Use the port monitor of the connected board to calibrate the values.

Final assembly of the device

Finally, let’s assemble the device. We pull the washer under the can to the bottom of the container with self-tapping screws, having previously lubricated with sealant. We put the empty jar in place, measure the indents from the sides and transfer the dimensions to the container lid. Cut out a hole along the markings and put on a thin silicone tube cut along the edge.

With an indent of 20–30 mm from the cut, we make a second hole 50 mm in diameter and install a computer cooler on four 60 mm screws, which will direct the air flow upward, removing steam from the container and making it easier to generate with a small vacuum. PVA 3×0.75 mm is used to connect to the power supply.

Now it remains to fill the jar with water to the brim, put on the assembled humidifier on top, turn the structure over and apply power.