I am trying to build a device that detects a running battery powered saw and send a signal to enable my shop vac.
To accomplish that I tried using a sound sensor.
First I tried using a digital sound sensor but I couldn't dial in the sensitivity to only trigger on really loud sound, it either was on almost all the time or never.
To compensate for a possible faulty sound sensor I bought a MAX9814 based sensor.
I changed the gain to 40db, otherwise pretty much everything almost maxes out the sensors value.
When testing it the results were pretty weird.
Tapping with a hammer on another table reached analog values above 900.
But cutting a board with the saw only reached 700ish.
Is there a way to make sense of the readings or is a (cheap) sound sensor not capable of doing what I try?
I mean hammering are singular noises and a saw will output a continouus stream of sound, maybe check for 10 high readings in a defined timespan to activate it or something would work?
You are not the first to find this snag, many people trying this sort of thing are not successful at all.
It simply does not work. Yes your ear can pick up things but the actual noise energy in the sound is insufficient. The best bet would be to try some form of sound recognition system where you train it to recognise the sound you want to be the trigger.
These links might help you:-
sound recognition:- https://www.eetasia.com/news/article/Data-is-King-for-AI-Sound-Recognition
AI - Google’s flagship machine learning library: “TensorFlow“
Recognising different sounds using AI MagPi98 page 30 (free download of past issues just search for them)
What you need is a frequency selective system. Perhaps a high-pass filter will allow your sound level to only work on frequencies generated by the saw to trigger your project.
I suggest to use a CT (current transformer) to reliably detect current flow in one of the band saw motor power leads, and use that signal to turn on the fan.
CTs are noninvasive and electrically isolated from the line power, but usually require some amplification to switch a separate AC circuit. Example tutorial
Oops, just noticed "battery powered" -- CTs are for AC power only.
I have used a vacuum traducer with great success. I run a 1/4 tube from the vac to the sensor. When the vac starts the sensor trips and turns on the dust extractor.
That sounds like something you should try. A hammer strike only lasts for an instant. I would try to determine when the sound level is above a threshold for a few seconds.
Do you suppose the sensor is triggering on the sound of the vacuum when it is on?