https://youtu.be/nuyNNEPm8Dg
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I own one of those. They work good. Like any of the cheap Chinese stuff, it's probably great for occasional use. But anybody doing real work would probably turn their nose up at it.
I have several of those up to 10 liters. I use them all day everyday. I had one fail so I bought another of the same size to figure out what components on the circuit
board that needed replacement. Fixed that one and have had no more problems...
The piezo transducers and driver boards are basically jellybean at this point on AliExpress. I was doing a high power 40kHz project a while ago and this was by far the cheapest source of ultrasonic gear. You can get a whole piezo and tuned horn for like $10. It's crazy.
That stuff on AliExpress is way inexpensive and it does work...
I bought a bunch of the transducers and a couple driver boards. The transducers were actually really good. The resonance of the transducer horns was all within a couple percent of 40kHz. We measured the frequency response of each one. I was pleasantly surprised.
I buy a ton of stuff on AliExpress and only had maybe three or four mishaps. They were all trying to buy car parts. Tried to buy an ignition coil for my girlfriend's Audi A4. It was worse than the one it was replacing. Tried to buy some mirror things to replace broken ones on my car and the seller just never bothered to ship them. Then I tried to buy a new MAF sensor for my Porsche 911 and it was a fake. I think they found a bin of manufacturing rejects and decided to sell them online. But other than those I've bought probably a hundred things, mostly electronics parts off of AliExpress and they've all been pretty good.
OH! No. Nevermind. I've probably bought 20-30 different types of antennas for an oceanographic project, and most of those were scams. They just grab a fistful of antennas from their big bucket full of antennas and tell you it's a <insert frequency you wanted to purchase here>. I tried to buy so many 915 MHz antennas, and maybe 25% of them were actually 915 MHz. Most people would never even notice because they have no way to verify it, but we were injecting signals on a VNA to get the actual frequency response. Mostly they were just buying tons of cheap mass produced 2.4GHz wifi antennas and selling them as any frequency. So I have a big pile of "915 MHz" antennas in my shop with sharpie pen marks of the actual frequency written on the side.
I saw one a couple of years ago that worked upside down. Put your parts in a container with fluid and float this thing on top. Video looked good but I have lost the link.
Thought it was a great idea.