The 74HC4046’s high impedance VCO control voltage input makes it particularly attractive so as to not load the transducer. The ubiquitous and inexpensive 74HC4046 phase-locked loop / voltage-controlled oscillator comes to mind. If I were designing this circuit I would use a voltage-controlled oscillator (VCO) whose frequency is automatically adjusted in a feedback loop by the detected transducer’s output amplitude. I’ve seen almost the same or similar circuit many times on the web (see example link below), but I have never seen a full circuit description. Why not just dump the inductor and the 100nF series cap and drive the piezo directly with the MOSFET? You don’t need the inductor to make the 555 a 113 KHz astable multivibrator, a simple RC network will work, and that’s exactly how this circuit does it. But that’s using the specified static capacitance of the piezo transducer, the dynamic capacitance (and other parasitics) are not specified at self resonance, and there’s no datasheet on offer. The Piezo’s capacitance is 1700pF which with the 220uH inductor and 100nF capacitor resonates at 262,449 KHz, not 113 KHz. What is the purpose of the 220uH toroidal inductor? Maybe the inductor is there to increase the peak voltage across the piezo transducer? I don’t think so, the transducer is rated for 5-12V and this circuit is using 15V already. Posted in home hacks, Science Tagged 555, atomizing transducer, cool mist, humidifier, mosfet, piezo, piezo disk, transducer, ultrasonic atomizer Post navigation They’re not picky about where the water comes from, so if you have enough of them, you can dry a load of laundry in a few minutes. Check out the demo and build video after the break.Ītomizing transducers can do way more than than moisten the air for our comfort. The circuit is designed for atomizing transducers, which have a resonant frequency of 113 KHz - much higher than your average junk box piezo. You don’t need much more than that and a handful of passives to recreate this cool junk box experiment, but the spec of the piezo disk is quite important. The driving circuit for this DIY mist maker uses a 555 to generate 113 KHz, a trimmer potentiometer to fine-tune it, and a MOSFET to amplify the signal. That energy introduces standing waves that force the water to break apart into a fine mist on the surface of the piezo disk. These work by using high-frequency sound waves to pound the surface of the water with mechanical energy. Some cool-mist humidifiers work by flinging water at a vaporizer, but our favorite kind uses a piezoelectric transducer.
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