Noisy input

A project log for Monitoring washing machines

One mans quest to spend less time in the basement

Lars KnudsenLars Knudsen 06/06/2016 at 16:321 Comment

For a while this project has been only frustrations figuring out how to get a script to run on boot, figuring out why the script stopped running at 6:24 in the morning two attempts in a row (and not stops at that time stamp anymore), some headaches implementing the microphone hardware and lack of resources and time. This post won't cover all the trivial challenges but instead focus on the results from switching the accelerometers out with microphones.

After deciding to try out microphones I quickly found out that I didn't have enough wire laying around to cover both accelerometers and microphones, so the accelerometers were removed for now - it was more important to explore if the microphone route was viable. Currently the microphones are mounted on the back of the machines with tape holding the surface of the electret microphone against the back of the machine. This seemed to work reasonably but I found if I could reduce the amount of ambient noise which would be detected by putting a piece of tape between the microphone and the machines. I believe there was a bit of electrical noise which this eradicated.

Running the machines show that this solution does not fix the cross talk I saw using the accelerometers. The orange line represent the washing machine and the green line the drying machine which is on top of the washing machine.

The wash took about an hour as expected, but all my test measurements so far show drying times below 1½ hours for the program which is estimated to last +3 hours. This project may just turn out to be very useful in getting a lot of laundry done over the weekend.

I was able to interpret the data myself and actually used it to check if my wash was done (had a party to attend so I was in a bit of a rush) so already the project has proven useful, but I was let down that it suffered from the same issue as the accelerometer approach. After staring at the data for a while, I noticed that even though there is cross talk, the seems to be a noticeable difference between the to measurements when either machine is running. I quickly produced the graph below which verified my hypothesis, eureka!

Difference between the two microphone readings

There is some filtering left to do, but it does look manageable. I'll probably try out a few different things along the way, I think a median filter before summing the values could make the readings less noisy and of course I can experiment with the sampling window.

I also have a bit of work making the script run stable, but I believe I am a cronjob with a nightly reboot away of being successful at that. I hope. At one point I considered logging ram usage to see if I had a memory leak, but then I realized that it would be a lot of extra work, logging and analyzing that to determine if there was a leak - and then I would also need to address it! Nightly reboot seems like the easy solution... [XKCD 1495]


PointyOintment wrote 03/29/2017 at 15:56 point

> I believe I am a cronjob

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