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**A Scary-Looking Pumpkin with a Twist**

Since Halloween is slowly approaching, I got myself a pumpkin, emptied its guts and tried carving it a scary-looking face. You know like everyone does during that time of the year. But for an electronics enthusiast like me, it is quite boring to just place a couple of small tea lights inside the pumpkin and be done with it.

**A Better Alternative: Ultrasonic Mist Maker**

A better alternative would be a so-called ultrasonic mist maker. By placing it inside a container filled with water and powering it over 24 volt power source, it creates a small water fountain along with a thin layer of fog. Of course the LED light show is a nice bonus, but the main point of this gadget is that, by positioning it inside the pumpkin, It makes it look a lot more interesting.

**The Cost: A Bargain from eBay**

Now, you can get such an ultrasonic mist maker for around $9 from eBay. But I also bought myself 2 ultrasonic piezoelectric disks from eBay for only $2 each. Those are the main components of the mist maker.

**A Question of DIY vs Buy**

The question of this DIY or buy episode is whether it would make sense to create our own driver circuit for such a piezoelectric disc, or whether we should just buy the commercial product instead? Let's find out.

**Taking Apart the Piezo Disc**

First off, let's remove the rubber sealing, and the spring from the piezo disc and have a closer look at it. As you can see there's really not much to it,

WEBVTTKind: captionsLanguage: enSince Halloween is slowly approaching,I got myself a pumpkin, emptied its guts and tried carving it a scary-looking face.You know like everyone does during that time of the year.But for an electronics enthusiast like me,it is quite boring to just place a couple of small tea lights inside the pumpkin and be done with it.A better alternative would be a so-called ultrasonic mist maker.By placing it inside a container filled with water andPowering it over 24 volt power source, it creates a small water fountain along with a thin layer of fog.Of course the LED light show is a nice bonus, but the main point of this gadget is that, by positioning itinside the pumpkin, It makes it look a lot more interesting.Now, you can get such an ultrasonic mist maker for around $9 from eBay,but a while ago I also bought myself 2 ultrasonic piezoelectric disks from eBay for only $2 each.Those are the main components of the mist maker,So the question of this DIY or buy episodeis whether it would make sense to create our own driver circuit for such a piezoelectric disc,or whether we should just buy the commercial product instead?Let's find out.First off, let's remove the rubber sealing, and the spring from the piezo disc and have a closer look at it.As you can see there's really not much to it, "Just a plain metal disc," you would say. But it's resonance frequency of1.7 Megahertz makes it special. If you were to place it inside water andstimulate it with a 1.7 Megahertz, AC signal,it would create a strong mechanical oscillation and therefore waves through the water.It is basically the same as when you pour water into a speaker cone and play back tones with different frequencies.The mechanical vibrations would create different waveforms on the surface of the water.By utilizing rather low frequencies the water can easily follow the movement of the speaker cone,but on the other hand, when creating1.7. Megahertz waves the water particles cannot follow the oscillating surface,And thus create a momentary vacuum during the negative amplitudes, which therefore creates air bubbles.That is why during the positive amplitudes tiny water droplets are catapulted into the air,quickly dissipate, and take vapor form.And now with the theory out of the way, how can we create the required 1.7 Megahertz AC signal?One way to do so is by utilizing a full H bridge, which consists of four MOSFETs.By turning on MOSFET one and three current would flow from left to right,and by turning on MOSFET two and four current would flow from right to left.Which is obviously alternating and thus an AC signal.As a first test I will use the full bridge that I pulled from my wireless energy transfer system.By connecting the piezo disc to the outputs,submerging it into water, powering the circuit with 12 volts, and measuring the oscillation frequency with an oscilloscopewe can slowly increase the frequency and search for the resonance point.Surprisingly though, the disc started creating a high-pitched sound at around 140 Kilohertz,but without causing any effect on the water,which was weird.But once I reached a frequency of around 1.7 Megahertz,the disc actually started to create a noticeable bulge on the surface of the water.And by lifting it out a tiny bit it was also capable of producing the fountain effect, and thus the mist.But since my full bridge circuit consists of four MOSFETs, two mosfet drivers, one 555 timer, one hex inverter,dozens of passive components, and a complicated schematic, It's not really worth building it for mist maker due to its costs.But at least we got a proof of concept, so let's get rid of the full bridge and let's try something simpler.The first circuit that I came up with was a true sign of my genius, since I drew a simple 555 timerpwm circuit that turns on/off a single MOSFET.After creating the circuit on a piece of perf-board,the 555 timer did generate the required resonance frequency of1.7. Megahertz and thus turned on/off the MOSFET accordinglyBut the problem was that this was still a DC voltage not an AC voltage which would let current flow in alternating directions,instead of just one.So obviously the piezo disc decided to do absolutely nothing.Brilliant.The next circuit I tried was a half bridge,which is simpler than a full bridge since it only consists of two MOSFETs while still being able to produce an AC signal.So I created a suitable schematic and soldered all the components to one another on a second piece of perf-board.After then powering the circuits and trying to adjust the frequency, I noticed another fatal problem, though.I utilized the IR2184 MOSFET driver since it features an easy to use bootstrap operation,only requires one control signal and includes a, dead time to keep cross conduction losses low.But if we combined the dead time with the turn on/turn off timewe can see that this switching process only allows a maximum frequency of around 690 KilohertzThat is why, while trying to increase the frequency up to 1.7 Megahertzthe MOSFET driver basically ignores the control signal at around 700 KilohertzNow I originally try to stay away from the IR2113, which I utilized before with my full bridgesince it requires an additional inverted signal, but since it came to this I soldered wire to its mandatory pinsedited Schmitt trigger next to it's to create the inverted signal andConnected them to the 8 pin sockets of the IR2184 MOSFET driverThis time I was capable of creating the 1.7 Megahertz, AC voltage across the piezo disc,but even after changing the capacitor values the disc did not react to the signal how I wanted it to.So as a last resort for the H bridge circuitry,I simply got myself an L293 IC, which is basically a premade H bridge.But after doing some calculations, I quickly realized that this H bridge would also have been too slow,Which led me to abandon the idea of using an H bridge completely and instead turned to an eBay sellerWhich supposedly offers a suitable oscillator circuit for the problem.After adjusting a couple of component values to what I had laying around I soldered all the components to one another in midair,since I was tired of perf-board soldering.Once my piece of art was complete,I powered it up, measured the voltage across the piezo disc, and was actually greetedwith an acceptable looking sine voltage.Only problem was that the frequency was around 140 Kilohertz, and thusnowhere near the required 1.7 Megahertz.Even changing component values seemed to not influence the oscillation frequency greatly,which led me to believe that this could be a problem with the disc having a second resonance point, which we also experienced earlier.So in conclusion,after creating five circuits, which were either too expensive,or complete failure.It would be wise to just buy the products instead of DIYing it, at least in my opinion.I hope you enjoyed watching my stupidity and at least learned something new along the way.If you have more ideas for DIY or buy episodes feel free to share them in the comment section.As always, don't forget to like, share, and subscribe,stay creative, and I will see you next time!