ultrasound, micros, FFT, and... sprayguns - Page 1
Forum section: electronics / projects

author: bill_c
author_rank: Regular Contributor
timestamp: January 04, 2021, 01:06:27 am
content: TLDR: What microphone, (arduino-ish) micro, and code would I need to detect a change in sound in the 40kHz range? What traps do I need to avoid? Is analog microphone better for this than a Pulse Density Modulation microphone? Is it as simple as using the arduinofft library with a fast board? Would I need some sort of enclosure around the microphone to duct the sound in or is it better to have the port just out there?I am spraying an adhesive with a compressed air paint spray gun. The adhesive cogs the fluid passage sometimes, and builds up on the outside of the air cap of the gun all the time. I cannot use a different glue or apply using different method or use a flow meter. I have done as much as possible to reduce the frequency of the problems, but they cannot be eliminated. Even with all the background noise of production, I can clearly hear the difference when there is buildup on the outside of the air cap, and just barely hear the difference when the fluid passage is clogged. So...I want to automate the spraying operation and what I would like to make (or buy) is a device to sense when the spray gun gets clogged. I will know when the gun is off, just air, air and spraying, so I can reference the background noise.Some online research shows that 20kHz to about 40kHz (usually around 40) is used to detect air leaks, which the gun is kinda like an air leak so maybe this is the range I should be listening to?All advice is welcome.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: January 04, 2021, 01:31:20 am
content: It's unlikely any conventional mic will help. You can buy ultrasound mics, e.g.,https://www.dodotronic.com/product/momimic/?v=2a47ad90f2aehttps://www.dodotronic.com/product/ultramic-um192k/?v=2a47ad90f2aeI would capture the analog signal as I would an audible signal and then, via FFT, calculate spectral energy in different bands (octaves would probably suffice) and look for changes in the >20kHz bands. Alternatively, I would bandpass filter the signal and just determine the average intensity of the filtered signal. Since what you are after is, in effect, just an in-process control measurement, you don't have to quantitatively accurate.

author: CaptDon
author_rank: Super Contributor
timestamp: January 04, 2021, 08:13:07 pm
content: I found a good 'cheap' ultrasonic transducer is those piezo-electrictweeter horns originally made by motorola that are about 2" squareand about 2.5" deep. Used to buy them dirt cheap, maybe $5 at radioshack stores for building home hi-fi speaker cabinets. They have anatural resonance around 26khz where they will both 'transmit' and'receive' efficiently. I built a distance measuring device using a pairof them since I didn't want to duplex/diplex the transmit and receivesignal on a single transducer. I know they can receive the screechesfrom bats to be displayed on a waterfall chart. They do have an intentionallywide dispersion pattern although that was wonderful for making a gainantenna by using it like a feedhorn in satellite dish style using a child's'flying saucer' as the reflector. We took received signals from bats andcar keys and so forth and ran through a balanced mixer with a variablelocal oscillator frequency to move ultrasonic frequencies down to the audiblerange. Extremely interesting sounds!!!!