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Detecting onion rotting/decay
Moderators: adafruit_support_bill, adafruit

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Detecting onion rotting/decay

by Nsukami on Tue Jul 30, 2019 8:29 am

Hello people, really hope you're doing fine. Really hope everything is okay on your side. I'd like to have some informations please.

I'm actually trying to build a module (Arduino + sensors) that will be able to detect onion decay/rotting. For that, I've first listed the gas that need to be detected:
- Carbonic acid
- Hydrogen sulfide
- Hydrogen selenite
- Hydrogène proto-carboné ou formène <-- I'm not sure about correct name in english
- Methane (maybe) <-- Not sure if this gas is actually emitted during the onion rotting process
- Amonia <-- detecting amonia means that the onion is completely lost/rotten and no more edible

And now, I'd like to know please, do you think you can find sensors for each of those gas? If yes, can you tell me the prices?
If you have any other advices on how to procede, please, let me know. Maybe you have a better way to detect onions rotting/decay.

Thanks a lot for your help and advices.

Nsukami
 
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Re: Detecting onion rotting/decay

by adafruit_support_mike on Tue Jul 30, 2019 2:24 pm

You can try using a Volatile Organic Compound sensor:

https://www.adafruit.com/category/897

Those don’t detect specific compounds, they just measure the way the air behaves when it’s heated.

Sensors for specific compounds are usually expensive.

adafruit_support_mike
 
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Re: Detecting onion rotting/decay

by adafruit_support_bill on Tue Jul 30, 2019 2:53 pm

This company has a selection of sensor modules for specific gasses. I don't have any first-hand experience with them, but their pricing is much lower than typical industrial-grade gas sensors: https://www.spec-sensors.com/product-ca ... nsors-iot/

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Re: Detecting onion rotting/decay

by Nsukami on Tue Jul 30, 2019 3:13 pm

adafruit_support_bill wrote:This company has a selection of sensor modules for specific gasses. I don't have any first-hand experience with them, but their pricing is much lower than typical industrial-grade gas sensors: https://www.spec-sensors.com/product-ca ... nsors-iot/

Already been there. The only specific sensor they propose and that is interesting for me, is the H2S sensor. They do not have specific sensor for the list I've sent earlier. But thanks a lot for your reply.

Nsukami
 
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Re: Detecting onion rotting/decay

by Nsukami on Tue Jul 30, 2019 3:16 pm

adafruit_support_mike wrote:You can try using a Volatile Organic Compound sensor:

https://www.adafruit.com/category/897

Those don’t detect specific compounds, they just measure the way the air behaves when it’s heated.

Sensors for specific compounds are usually expensive.

May I ask please, did you try it? For what project? Thanks a lot for the advice, I'll have a look.

Nsukami
 
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Joined: Tue Jul 30, 2019 8:24 am

Re: Detecting onion rotting/decay

by Nsukami on Tue Jul 30, 2019 3:20 pm

adafruit_support_mike wrote:You can try using a Volatile Organic Compound sensor:

https://www.adafruit.com/category/897

Those don’t detect specific compounds, they just measure the way the air behaves when it’s heated.

Sensors for specific compounds are usually expensive.

May I ask please. For the Adafruit BME680 - Temperature, Humidity, Pressure and Gas Sensor for example, is it said that
- "it will give you one resistance value, with overall VOC content, but it cannot differentiate gasses or alcohols."
- "you will want to calibrate it against known sources"

May I ask what is the meaning of this sentence:
- "We recommend that you run this sensor for 48 hours when you first receive it to "burn it in", and then 30 minutes in the desired mode "


If I correctly understand, I'll needto :
- use the sensor in a perfectly clean area, get the resistance value A
- use the sensor again in an area full of rotten onion, get the resistance value B

And in the future, everytime I'll get value B, I'll know I'm in the presence of rotten onion. Correct?

Nsukami
 
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Joined: Tue Jul 30, 2019 8:24 am

Re: Detecting onion rotting/decay

by adafruit_support_mike on Wed Jul 31, 2019 12:04 pm

Nsukami wrote:May I ask what is the meaning of this sentence:
- "We recommend that you run this sensor for 48 hours when you first receive it to "burn it in", and then 30 minutes in the desired mode "

The BME680 uses a heater to burn organic compounds in the air, and detects the burning as a change in the resistance through the heater. It measures the heater’s resistance, and you can interpret changes in the measured resistance to mean some kind of VOC is in the air.

The heating element will develop a layer oxide and residue from compounds in the air over time, and those also change the measured resistance. A brand-new heating element doesn’t have that layer, so you’ll see the readings from a new sensor change, even in clean air. After about 48 hours of continuous use, the oxide/residue layer becomes uniform enough that it no longer has much effect on the readings.

The burn-in period gives the sensor time to become stable in the environment where you’re using it.

Nsukami wrote:If I correctly understand, I'll needto :
- use the sensor in a perfectly clean area, get the resistance value A
- use the sensor again in an area full of rotten onion, get the resistance value B

And in the future, everytime I'll get value B, I'll know I'm in the presence of rotten onion. Correct?

That’s close, but the results won’t be that simple.

Run the sensor for 48 hours to let it develop the oxide/residue layer, then run it in clean air to get value A.

From then on, readings near value A will mean the sensor smells clean air. Readings farther away from value A will mean the sensor smells some kind of VOC. The value depends on the mix of VOCs and the overall concentration of them in the air, just like the same smell gets weaker or stronger depending on how much there is.

You won’t get a single value that means ‘rotten onion’. You probably won’t get the same reading from two different onions, and the reading for the same onion will probably change over time as it rots further and emits more VOCs.

In practice, you’ll find a value B that means ‘probably detecting early signs of rot’.

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Re: Detecting onion rotting/decay

by Nsukami on Sun Aug 04, 2019 6:37 pm

adafruit_support_mike wrote:That’s close, but the results won’t be that simple.

Run the sensor for 48 hours to let it develop the oxide/residue layer, then run it in clean air to get value A.

From then on, readings near value A will mean the sensor smells clean air. Readings farther away from value A will mean the sensor smells some kind of VOC. The value depends on the mix of VOCs and the overall concentration of them in the air, just like the same smell gets weaker or stronger depending on how much there is.

You won’t get a single value that means ‘rotten onion’. You probably won’t get the same reading from two different onions, and the reading for the same onion will probably change over time as it rots further and emits more VOCs.

In practice, you’ll find a value B that means ‘probably detecting early signs of rot’.


Thanks Mike for all your explanations, it helps a lot.

It sounds like that way of doing will be less precise enough with time passing. But I keep it under the elbow. Thanks for the suggestions.... To conclude, I will have 2 options (correct me please if I'm wrong):

1 - Do, as described earlier by Mike
2 - Use the H2S sensor: https://www.spec-sensors.com/product/di ... ensor-h2s/ because Hydrogen Sulfide H2S is emitted during the rotting process. We can just detect this gas and we'll know the rotting process have begun.

Nsukami
 
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Re: Detecting onion rotting/decay

by adafruit_support_mike on Sun Aug 04, 2019 10:25 pm

The H2S sensor should be more selective, yes.

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Re: Detecting onion rotting/decay

by czuvich on Mon Aug 05, 2019 11:10 pm

If gas detection is not feasible, I bet you could use pictures. You would use a camera to upload a picture and analyze on the backend. It’s more work, but may be easier.

czuvich
 
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Re: Detecting onion rotting/decay

by Nsukami on Fri Aug 09, 2019 6:43 pm

czuvich wrote:If gas detection is not feasible, I bet you could use pictures. You would use a camera to upload a picture and analyze on the backend. It’s more work, but may be easier.

Good idea indeed, we thought about it, but No. There won't be one onion, there will be lots of them, and they will be packed like in this picture: https://images.app.goo.gl/bvB9ij8NJjeN1QGH6 Thanks for proposing.

Nsukami
 
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Please be positive and constructive with your questions and comments.