[{"data":1,"prerenderedAt":185},["ShallowReactive",2],{"project-14758344":3},{"id":4,"name":5,"line":6,"line_source":7,"title":8,"url":9,"domain":10,"maker":11,"posted_at":12,"year":13,"points":14,"comments":15,"rank_in_year":16,"shown_in_year":17,"top":18,"tier":19,"category":20,"subcategory":21,"format":20,"keywords":22,"reception":26,"sentiment":27,"stance_mix":28,"scored_comments":33,"aspects":34,"strip":38,"post_text":40,"what":41,"said":51,"maker_in_thread":102,"shape":111,"grid":116,"attempts":145,"same_week":146,"maker_shows":176,"maker_hidden":177,"reader_version":178,"card":179},"14758344","Bubbleometer","An attempt to measure fermentation activity from the sound of bubbles","title","Show HN: An attempt to measure fermentation activity from the sound of bubbles","https:\u002F\u002Fwww.anfractuosity.com\u002Fprojects\u002Fbubbleometer\u002F","anfractuosity.com","anfractuosity",1499913480,2017,27,13,1085,2242,49,"shown","hardware","fermentation monitoring",[21,23,24,25],"bubble detection","audio analysis","homebrew","curious",-0.119,{"positive":29,"neutral":30,"mixed":31,"critical":32},1,3,0,2,6,{"execution":35,"idea":36,"performance":37},{"positive":31,"critical":29},{"positive":31,"critical":29},{"positive":29,"critical":31},[30,31,29,31,30,29,31,39,31,30,31,31,31],5,null,{"problem":42,"audience":40,"pricing":40,"motivation":40,"time_to_build":40,"stack":48,"openness":49,"stage":50,"team_size":49},{"value":43,"source":44,"evidence":45},"Measuring fermentation activity from the sound of bubbles","maker",[46],{"id":47},"post",[],"unknown","prototype",{"praise":52,"objections":65,"requests":76,"questions":77,"alternatives":84},[53],{"value":54,"source":55,"evidence":56},"Commenters liked the approach and offered signal processing ideas","commenter",[57,61],{"id":58,"by":59,"text":60},"14760604","supernes","Sampling at 48kHz seems like overkill. If you record at a lower sample rate (e.g. 22k) you will still be able to detect the bubbles, but the files will be about 4 times smaller,…",{"id":62,"by":63,"text":64},"14769320","cocoablazing","Since bubbles popping are a random and impulsive source, the spectrum of the detected noise will be the resonance of the glass plus a white noise floor. 48khz is not overkill.…",[66,70],{"value":67,"source":55,"evidence":68},"48kHz sample rate may be more than needed",[69],{"id":58,"by":59,"text":60},{"value":71,"source":55,"evidence":72},"FFT smears the signal in time; squaring the signal may work better",[73],{"id":74,"by":63,"text":75},"14769351","You are better off squaring the signal. Applying an FFT to get the magnitude will smear your signal in time. I suggest you look into acoustic emission detection.",[],[78],{"value":79,"source":44,"evidence":80},"Which correlation function to use for spectral matching",[81],{"id":82,"by":11,"text":83},"14760929","Yeah I agree with respect to the sample rate. I wasn't really sure what sample rate would be best when I started recording the audio, so just picked the highest the soundcard…",[85,95],{"value":86,"source":55,"evidence":87},"CO2 gas sensor (MQ-135) near the airlock to detect bubbles",[88,92],{"id":89,"by":90,"text":91},"14764427","roevhat","Awesome! I attempted the same approach, but after discovering a cheap gas concentration sensor (MQ-135, tunable to CO2) I abandoned the audio approach for a minimum of data…",{"id":93,"by":90,"text":94},"14768176","I put it near the airlock and detect peaks. For now, the most valuable information I extract is when the fermentation starts and stops -- with notifications on my phone :-)",{"value":96,"source":55,"evidence":97},"Plaato fermentation monitor",[98],{"id":99,"by":100,"text":101},"14770878","devopsproject","https:\u002F\u002Fwww.plaato.io",{"comments":39,"answered":32,"key":103},[104,105,108],{"id":82,"text":83},{"id":106,"text":107},"14769361","Thanks! I'd not heard of acoustic emission detection, I'll look into that now. Do you think my sample rate is high enough for acoustic emission detection, as I notice in your…",{"id":109,"text":110},"14764470","Ooh that sounds very interesting, I'd be interested in how that works, do you put the co2 sensor near the airlock and notice 'peaks' of co2 from it, when bubbles come through. 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