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Forum Index : Microcontroller and PC projects : HUMID CSub...
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| Author | Message | ||||
Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Howdy.  Can someone help me understand the results for the humidity. The results I get back are always 100% when the sensor is dry, and the percentage gets less if I puff some steam into it. According to one person I was talking to, it should be 100% when really moist air, and getting closer to 0% as the air gets drier and drier. So, getting a reading of 100% for dry air is totally round the wrong way. Is that right, or is my chum putting me crook? ....now the seed of doubt has been planted.  That does sound kinda correct though. 100% Humidity suggests it is a really moist air, but now I might be totally misunderstanding the damn thing.... Smoke makes things work. When the smoke gets out, it stops! |
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| PeterB Guru  Joined: 05/02/2015 Location: AustraliaPosts: 655 |
G'Day Grogster. Are you talking about humidity or relative humidity? Things like the DHT22, HTU21D, BME280 etc measure relative humidity which is the amount of moisture in the air expressed as a percentage of the maximum (saturated) amount. That's probably not a good definition but if I try to improve it I will probably trip over and hurt myself. The more moisture in the air, the higher the percentage. Very high relative humanities often occur on a cold crisp morning which is not quite the typical hot humid tropical climate we all understand so RH is a bit more complicated than we think. However, I would have expected the opposite of what you are getting. Peter |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
The HUMID Csub works for me. Make sure you have the pin as an integer and the other two varaibles as floats. The sensor also send the previous reading each time you read so it needs two reads to get a current reading. Jim VK7JH MMedit |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Yeah, it works fine. That's not the problem. The problem is that I don't know if a result of 100 from the humidity float returned by the CSub, means 100% as in totally full of moisture(as my chum thinks it should be), or totally dry air(as the CSub suggests it is). Confused....  Smoke makes things work. When the smoke gets out, it stops! |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
100% is a steam bath. 20% is a very dry day. VK7JH MMedit |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
OK, that's a good starting point. So how come whenever I read the sensor, it reports 100% humidity when it is dry as an old stick, and a lesser value when I puff it with some steam? What you say tallies with what my chum was saying, but it is NOT what I am getting back from the CSub. It's always 100% when dry as a bone, and less then that when I puff steam into the sensor. Smoke makes things work. When the smoke gets out, it stops! |
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| Frank N. Furter Guru Joined: 28/05/2012 Location: GermanyPosts: 949 |
Hi Grog, when I worked as an optician in my former life, we adjusted the hygrometers as follows: Wrap the hygrometer in a wet cloth, wait 5 minutes and adjust to 98%... Something is wrong with your values... Frank |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Danke mein Freund. Ich lerne immer noch Deutsch, sorry, falls das falsch ist. [Quote=Translation] Thank you, buddy, I'm still learning German, so this might be wrong. [/Quote] I agree. Something wrong. I will sleep on it, and re-address it again tomorrow. Smoke makes things work. When the smoke gets out, it stops! |
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| Frank N. Furter Guru Joined: 28/05/2012 Location: GermanyPosts: 949 |
Hey, your German is perfect and much better than my English!!!  (What would I do without www.deepl.com...  )Frank |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
I think PALCAL had a problem with DHT22s. He chucked a lot away. Did you get yours from his bin? OR, do you have a dud chip? Saturated NaCl solution gives RH = 75% Peter |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Yes, I did read that thread by palcal, but I verified my ones as certainly giving the correct temperature reading. I think he was also having HUMIDITY issues though, so perhaps.... I am using the AM2302 device, but I think it is just a DHT22 with a different part number printed on it. I will have another read of his thread. Smoke makes things work. When the smoke gets out, it stops! |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
@ Grogster I had no trouble with temperature but the humidity was all over the place some did not work at all most were out by more that 10%. I must have ditched at least 6 , I have one left that is out about 3% out which is acceptable. I am using HTU21D's and they all work well. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Hey there. How did you find soldering that device? I see it is a DFN, and has no legs.... Smoke makes things work. When the smoke gets out, it stops! |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Using a MX170 with MMBaasic Ver5.04.01 CPU speed is 40 Code is running on my testserver. 16:43:40 T(BMP085): 23.2 P(sl): 1009.6,T(DHT22): 22.2 H: 53.4,T(DS18B20): 22.5 16:43:50 T(BMP085): 23.3 P(sl): 1009.9,T(DHT22): 22.2 H: 54.2,T(DS18B20): 22.5 16:44:00 T(BMP085): 23.3 P(sl): 1009.8,T(DHT22): 22.7 H: 99.9,T(DS18B20): 22.7 16:44:10 T(BMP085): 23.4 P(sl): 1009.8,T(DHT22): 24.6 H: 99.9,T(DS18B20): 22.7 16:44:20 T(BMP085): 23.5 P(sl): 1009.9,T(DHT22): 25.1 H: 99.9,T(DS18B20): 22.7 16:44:30 T(BMP085): 23.5 P(sl): 1009.8,T(DHT22): 24.3 H: 99.9,T(DS18B20): 22.7 Room humidity was 53% until I did some heavy breathing which sent it to 99.9% Humidity was back down to 60% after one minute. The AM2302 is the same beast as the DHT22. I have used modules branded as either without problems. They do suffer from over exposure to light or sustained high humidity. I expect them to last 3 years or so before replacing. Jim VK7JH MMedit |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
I have elected to go with the BME280 for TEMP & RH for a project to calculate delta T??. Is that a good choice? Peter |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
BME280 should be good. Jim VK7JH MMedit |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
I also like this device now, as it comes on a board of it's own. I will have to get some of these to play with. Smoke makes things work. When the smoke gets out, it stops! |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
Thanks Jim. I have ordered 2 @ $5 each but they are a couple of weeks away. This waiting kills me Peter |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
"The waiting is the hardest part." - Tom Petty Smoke makes things work. When the smoke gets out, it stops! |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 655 |
So now I know who Tom Petty is. Thanks. You keep throwing quotes from un-heard-of musos at me. Do you remember? Peter |
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