$105.05 is slightly more than $20

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Bill
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Yeah, went a little crazy shopping. Still on track for the $20 goal though.

HH10D Humidity Sensor $9.90
HP01D Barometer Pressure Sensor - HP01D $5.50
CRY32 32.768kHz Crystal $0.75

Should have everything else already. Most of this order was connectors (IDC, header sockets), and a few other odds and ends that are getting scarce around here. Futurlec has the best prices on these, and don't order often.

 

Sounds like you still need more parts, a microcontroller, PCB?

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Bill
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I bought the cheaper module, but they all say '2 wire SPI'. The sensor in the picture for the HH10D looks different. Should be okay though, the datasheet says there is a Frequency Out pin, and is in the range of 5kHz-10kHz. Need to do some more reading. Also have some BASCOM code for reading these modules, so should be good one way or another.

 

I've got a spare bedroom for a lab, and quite an accumulation of parts...

I make my own PCBs (toner transfer).
I have on hand;
ATtiny11, 13, and 85, but only 8 pin so not suitable
Attiny2313 and Attiny26, either should work for this, thinking 2313 have more
Atmega48, only have 4, and kind still working on that project...

Also have some PICs, no idea why I save them. Pulled them out of something I scrapped, cable box or something.

Hardware shouldn't be a problem, need to read up on SPI and I2C, the MCU datasheets, and get ready.

 

Sounds cool, keep us posted.

Always wanted one of these.
http://www.aagelectronica.com/

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Bill
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Found an interesting bit on Atmel's website. There was an appnote about thermally correcting the ADC. Seems some AVR chips have a built in temperature sensor (diode), which can be read, and used with the ADC. Didn't see a list of chips in the PDF, but will look for it when I looking through the data sheets.

We had some thunderstorms yesterday, was kind of thinking about a lightning strike indicator. Probably a little too much for this project, something to add on later after this is built.

Have had some thoughts on the temperature reading though. Measuring indoor temperature probably wouldn't be the most useful, since most people use heating/AC to maintain a certain range of comfort. Also will need some method of adjusting min/max range for each sensor, and set the scale according to what is most useful. Maybe I can make it self learning in software, just store the lowest/highest readings in EEPROM. Wonder if all this will fit in 2k, or if I'll need to move up to a bigger chip.

 

Lightning strike indicator is a good idea. I hadn't thought about that for mine. Should be very easy. A small antena from radio or even a piece of wire, feed that to a simple diode detector and maybe and op-amp. Should be able to pick those babies up easy enough.

Michael

 

How are you going to run the data from the sensors? I2C is not terribly fond of long cable lengths.

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Bill
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I wasn't going to run them any place, just stuff everything in a box under the lamp. Air pressure should be the same indoors or out. Humidity will be a little lower indoors, but not a big enough difference to have any effect here. The temperature part... will likely stick with the indoor temperature for this first one. I don't run the heat or AC unless dressing accordingly is of little help. It's really more about changing conditions, not measuring how much of a change.

The lamp should stay in the same basic color range for the various weather conditions. A radical color change, would indicate storms coming...

 

Sounds like you only really need to pay attention to the Barometer Pressure Sensor. Typically, impending storms or bad weather can be detected by the relatively fast drop in barometric pressure:
http://www.weatherhut.com/site/12989...metricPressure

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Harvey would not want to use this but others may find the hair hygrometer of interest.

Hair changes length depending on humidity. On more humid days, hair will lengthen.

The diagram below shows a simple hair hygrometer. It takes about a foot of hair to create a sensor but it could be wound around a pulley or two to decrease the length. The pointer could be used to block light between a LED and a photo transistor for sensing.

Image about.com.

EDIT: Horse hair can also be used and may be more durable.

Attached Images

hair_h.png (8.9 KB, 9 views)

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I have to disagree. Might want to actually do a test of that assumption. I have a guage set of meters for all the above. I can take it from the house to outside and the humidity can vary a LOT.

Think about it. Unless you're fanning doors or have windows open the inside is isolated from the outside. Plus if you're running either A/C or heat it's going to change even more depending on the type of heat.

It will try to even out but it usually takes quite a long time based on how much air flows in and out of the house. If you're dead set on it being inside you could set it on a window sill with a window cracked open to get as close as possible.

Michael

 

Yeah, I get what yo mean. This isn't going to be something I figure on moving around much or carrying in my pocket. The actually readings for indoor and outdoor humidity will be different, but there should be similar changes. Like right now, it's cold and dry air. Humidity might be a little higher indoors (shower, coffee maker, people/pets), but different than yesterday, which was warmer but wet.

The readings I take, will be crunched down to an 8 bit value, to set the pulse width for each color of an RGB Led. Hopefully, I'll notice which colors and intensities indicate what sort of weather to expect. Could turn out to be as useless as the local TV news, or might make for a pretty neat gadget. Wonder if some Chinese company will have something like this on the market, before I get my parts from Futurlec?

 

I saw something like that when I search for weather related science fair projects. Figured it wouldn't last more then a few days or weeks. My hair is llong enough, fairly strong. My thought was to hook the hair to a light spring, and use the spring for the coil in an oscillator. Stretching the coil should change the frequency. Figured It would be very subtle, an kind of involved getting into a microcontroller. Would be nice to find a cheaper humidity sensor for this project. The one I ordered is $9.90, about twice any other part in the project, so still keeping my eyes open for alternate sensors. Mostly, I want to get something thrown together, just to see if this idea was any good, then work on making it simpler and cheaper. I don't think I get away with just making one or two if it works out.