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simple and low cost sensors

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cd6

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homemade humidity sensor

hello ppol!
my thesis group is putting up a project, which is an automatically controlled environment replicating a fully-automated and isolated greenhouse. most of its environmental factors will be simulated. we would be using several sensors of which the most important are light, temperature, and humidity sensors. these sensors would trigger other hardware to adjust their output depending on the programmed specifications.

i was wondering if anyone has an idea of what light, temperature and humidity sensors are available.

would it also be possible to come up with our own/improvised sensors, without compromising its functionability? how? if so,which would turn out cheaper, buying these sensors or building them?

thnx!
 

BeeBop

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homemade moisture sensor

Hi,

Perhaps the easiest to use temperature/humidity sensor is the sht11, but it is also expensive. I haven't used these yet, but they seem like a nice easy way to measure humidity, and as a bonus, they do temperature.

I have used the Humirel HS1101, but these take a fair bit of work. You need to set it up as a capacitive load in an oscillator, which will output a frequency dependant on humidity. The output is non linear, so you will have to do some calculation. Additionally, these are cheaper than the SHT11, but not by very much.

I would not try implementing my own humidity sensor; seems like it would be quite difficult, and time consuming.

For the light sensor, I'm thinking a photo resistor in the feedback circuit of an op amp should do the trick nicely. I have this on my to do list, but haven't started working on it yet.

I like your project, as it seems along the lines of some of what I'm doing now.

Best of Luck,
Robert
 

zeeshanzia84

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homemade sensor

Well a wonderful temperature sensor is LM35. It gives 10 mV/C starting at 2C.

Thus you get 10 mV output at 3C
20 mV output at 4 degree centigrade
.
.
.
upto 150 degrees

...
simply has three pins..




one homemade sensor for humidity can be obtained if you scratch and remove the surface (covering) of a simple discrete resistor. The resistance will change whenever it absord more/less moisture, which can be measure using a wheatstone bridge or some current source/voltage measurement configuration.
 

BeeBop

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how to use humirel hs1101

Hi zeeshanzia84,

one homemade sensor for humidity can be obtained if you scratch and remove the surface (covering) of a simple discrete resistor. The resistance will change whenever it absord more/less moisture, which can be measure using a wheatstone bridge or some current source/voltage measurement configuration.
Hey, this sounds great, but is it reliable? Have you ever tried it? It would be a heck of a lot cheaper than any humidity sensor I've come across. I'm going to give it a try when I get some time, it would be really great if it works well!

I agree about the LM35.

Regards,
Robert
 

cd6

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hs1101 datasheet

robert,thnx! indeed the hs1101 sounds a bit complicated. so,are u like doing an automated/system project or mostly sensors?

zeeshanzia84
yep,we did come across the lm35. how accurate is its ouput?
 

BeeBop

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moisture sensor 555

Hi cd6,
The Humerel is easy, hardware wise, there is a circuit with a 555 in the data sheet which works. The crappy part is that the frequency it puts out is not linear, so to give a really accurate output, you would need to use a table look up, or similar. (at least with an 8 bit micro)

You didn't say what you are using for a processor. Are you logging the data as well?

What I'm doing is probably a bit similar to what you are doing; it all boils down to controlling the environment. Right now there is a resistor on my desk with part of the cover removed. ;) I haven't got futher than that just yet, though. I think zee's idea is worth a try, just to see how well it'll work.

The LM35s are pretty accurate. They'll give you an analog voltage, and they're pretty easy to use. There is also the ds18s20 which is the one wire interface. Very nice indeed.

Later,
Robert
 

pqtam

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humidity sensor thesis

Hi,
1. Light sensor: use transistor (2N2222 etc) with metal case, carefuly cut the top of the case, carefuly clean up the silicon grease (be careful, not to damage the wiring from the cristal to the output legs). The transistor can now work as phototransistor with enough sensitivity. Use a small lense to increase sensitivity if required, but I think you don't.
2. The above transistor can also be used as temperature sensor, using base-emitter junction, short-connecting collector to base.
3. Use 5W or 10W carbon resistor, move away the carbon film with abrasive paper, wind-up the base of the resistor with thin (.01mm) manganin resistance wire and solder the two ends of the winding to the legs of the resistor. This like a technology of making metal wire resistance. The resistance is nearly linear with humidity change, especialy above 60%.
They are quite cheap, I have used them long ago.
 

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