HarveyH42

Wondered if anybody has any cheap/simple solutions or links for some basic weather related sensors. Looking for barometric, temperature, and humidity. None have to be particularly accurate, but should be easy to read/interface with a microcontroller (AVR, of course).

From the web so far, Freescale makes an air pressure sensor, but its about $20. Little bit more then I was looking to spend on this whole project. I just need to know if the pressure is rising or falling in whatever range is normal around here. Will look into science fair type projects, remember there were several simple means as a child, perhaps something can be adapted. Accuracy is unimportant.

Remember several threads on humidity sensors here, so will do some searching.

Temperature is the simplest, several cheap choices, but would like to here some alternatives, as I don't need any accuracy for this project idea. Remember some semiconductors (transistors) can be used, but don't remember the specifics, or if it would have much ranges, or require amplification (digging back 30 years or more hurts my brain...).

Guess I should explain the idea (save on some of the questions later). I was thing of an RGB Moodlight type lamp, but each of three LED's brightness is related to the three sensors. Basically a clear sunny day would be of some color range, stormy weather another. Based on what sort of color the lamp is, I should be able to guess what kind of weather to expect. Figure it'll be about as accurate as the local tv news . This is why the sensors don't need to be accurate, as I'll just be translating the reading into a PWM brightness level.

I'm on vacation this week, and currently waiting for the ups guy (chick last time) to deliver a solar panel (need to sign), for a different project. Been thinking about this one for a while, just kind of stuck in my head since I woke up this morning. Damn dog gets me out of bed around 7 am every day I'm off work, by jumping on the bed, across my stomach. Least he hasn't nailed me below the belt yet, but still not a great way to start the day.

3v0

I do not know how to make an inexpensive dry bulb humidity sensor.

For an idea regarding a wet bulb humidity sensor check this page. Should work with most any temp sensor type but I like the 1 wire units.

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BeeBop

You need to take the hyphen out of the link; ie: wetbulb.shtml, rather than wet-bulb.shtml:
http://www.digitemp.com/wetbulb.shtml
But thanks for that!

HarveyH42

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Mon Feb 25 11:16:55 2008
Apache

I've been finding quite a few one wire sensors, still a little above the target. Futurlec had a couple that I'm thinking about, if I don't stumble across something better. Both the humidity and pressure sensor modules are I2C, and also read temperature. One was under $6 the other $10. The price is nice, but about 3 weeks for delivery (if I'm lucky).

Found out the is a barometric pressure sensor in cars, unfortunately I junk my three lawn ornaments last December...

Still waiting on UPS, should probably check the website and see if it's still on for today.

blueroomelectronics

Problem is the $20 budget won't go far.

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BeeBop

See the link I posted.

3v0

Sorry about that folks. Wetbulb became wet-bulb when I did the spell check and I failed to notice it was in the URL.
But Bill is right. That is a very small budget to do much more then meausre air temp. With the sort of gadget you want to build the web bulb would be a bad idea but it is the only one you can afford.

EDIT: I would LOVE to be wrong on this one.

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HarveyH42

It's not really a budget, more of a goal. I'll spend what I need to to get one running. Just don't want to get too crazy, just in case I end up making more. I get talked into production work with some of my little gadgets (family, friends, neighbors...), also might be a suitiable project for a 'final-year' student with only a week or two before graduation...


Got the wet-bulb link, don't think it's something I can use for this (have to occasionally add water...), also a lot of PVC, maybe $20 dollars worth of fittings. Really only need a very rough measurement,I can scale and adjust in software.

Kind of looks like Futurlec has the best price. Going to search and see if I can find something on the web, that uses the modules. Both do temperature, so with shipping, ought to be around $25.

kchriste

You can use a diode or transistor as a real cheap temperature sensor:
http://www.overclockers.com/tips12/
You don't have to use a bridge circuit as the author has done. You just need to bias the diode and an Op-Amp to scale the output into AVR territory.
Here is a windspeed indicator that uses no moving parts:
http://www.fonema.se/anemom/anemom.html

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Gayan Soyza

You told that accuracy is not an important so In your case I use LM series Temperature sensors 34 or 35.Works fine & also cheap.Its rated upto 100 - 150C but I have measured temperature more than that.

Forgot to tell you can measure the light in the atmosphere too.To determine whether is is night or day time or how dark it is.

Use LDR for that, measure the AD reading & apply to the output.Most sun trackers use LDR's as sensors to identify the suns direction.

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mrmonteith

Try this:
http://www.c-stamp.com/sensors.htm

Michael

HarveyH42

Thanks for the link. Its the same 'made in china' SHT11/15 that Futurlec has, just a little more expensive. Little cautious that they make no mention of the actual part number, just their house branding.
The good part, they give good info on reading from it. I don't do 'C', but should still be able to get some useful bits out of the documentation.

Futurlec only has the datasheets. I did find a couple of BASCOM routines for reading the sensors. Didn't see a routine for reading temperature in them, but was just a quick look.


Thanks for the other suggestions for windspeed and light sensors. Not really looking to build a weatherstation in the backyard sense, this is more a desktop or shelf.

While searching, I ended up at the Edmund Scientific website. Remembered they had really cool, but expensive stuff when I was a kid. Didn't find anything I could use, but found they have something similar to what I'm working on. Theirs is hooked up to the internet, and the lamp color is set by whatever it's set to monitor (doesn't have to be weather). Should have grabbed the link, but it really wasn't useful here. Mine will be stand alone, and take its own readings.

Will order from Futurlec when I get from walking the dog. Looks like the best deal, and simplest modules availiable. Kind of a cool bonus that I can take a temperature reading from either the humidity or pressure sensor. Saves me time, money, and I/O pins, likely some code as well. This is coming together quite well.

HarveyH42

Just got back from walking the dog, checked out the diode temperature sensor. Think I'm going to play with that some. I bought 1000 1n914s a couple years ago for $5, maybe used 30 of them... Will have to do some math, but looks like a single resistor, a capacitor, and the diode are all that's needed for an input to the AVR ADC. Don't need this for the weather project, since I should be able to read the temperature over I2C from either module.

Will have about a three week wait on the modules, so a good time to get on building a simple LCD serial display/terminal. I downloaded the project files a while ago, figured it be a good tool to have, just never got around to it.

HarveyH42

I placed my Futurlec order a couple of hours ago. Came to $105.05, with the 'Express Shipping' ($16). It says 3-6 days, where standard shipping was about $9 and 2-3 weeks. Figured I'd give it a shot, still expect about 2 weeks until delivery. I got two of each sensor, but mostly I stocked up on sockets, plugs, and connectors, crystals, and few other odds and ends that I always seem to forget.

Pommie

Harvey,

Are you aware that the SH15 is not an I²C device, although it appears to be very similar.

Mike.