Slow progress

A project log for Electronic nose to detect fruit ripening

Can we get fruit trees to report to us when their fruit is ripe?

craigCraig 03/10/2017 at 22:560 Comments

Following up from our pear experiment

Well unfortunately I was not able to get much of a signal out of measuring a pear. That's a shame because it's one of the fruits we try to harvest in large amounts.

Once I had the chamber somewhat better sealed, this is the best data I was able to get... about 5 days worth. Unfortunately, there's not much of a clear signal here. Stuff is increasing, but it's also got a lot of wander to it and would be hard to determine a GO/NO-GO threshold from this.

There were still sealing issues: a lot of those large spikes appeared when I sat down at my computer next to the sample chamber and this was super frustrating cause I thought I sealed it really damn well.

Two holes, both with o-rings. All the existing holes were covered with the nice aluminum-foil sealing tape that conforms really well. I don't know what else I have to do here... I can sit down and watch the signals slowly start to climb. Very frustrating.

Of the data I got, if we take our strongest signal (A1 -- MQ3 alcohol sensor) and plot it in relation to temperature, we can see a pretty strong relationship:

You can see that there are several periods where the data decrease in a linear fashion and then increase in an almost identical fashion. It's sort of like someone is writing the letter 'm' over and over.

Furthermore, these linear relationships all have about the same slope, and I'm saying that's our temperature compensation coefficient:

These lines all have a slope between 0.125-0.154. The value I ended up using was 0.1313, but it probably doesn't matter that much.

I'm really trying not to imagine things in the data here. I'm restricting myself to the areas where the sensors decrease and increase along the same linear path because those don't make physical sense with sensing a gas emitted by a fruit but they do make physical sense when considering an oscillating temperature relationship.

Taking our 0.131-ish slope and compensating, we get:

This graph has the original data (blue), the measured temperature (green, and multiplied by 5 to increase its contrast on the graph scale), and the corrected data (orange). Overall it did a decent job of taking a wobbly signal and making it pretty straight. We do have a signal hidden in there, but it's just not very strong.

One other thing to note: when I ended this experiment, I took the pear out and tried eating it. It was TOTALLY GROSS. It had absorbed whatever rubber chemicals had volatilized from my big 10-conductor cable and just tasted like sweet weird rubber. It was super disgusting and I couldn't take more than 2 bites and I regret swallowing them. So there's something to be said for a new setup entirely that doesn't use that cable.

Next steps

A bit dejected after this one honestly. My thoughts at this point are to get as much wireless as I can so I can completely self-contain the electronics. Benefits of this: