rctime based weather station

Cogburn

I have a student that wants to build a weather station based on the BS2.· As I have 110 students to help along with projects, I don't have the time to be fancy with the programming or the money to buy hardware.· I was thinking about using rctime to gather wind direction, temp, rainfall, and windspeed data.· I need a cheap, quick and dirty way to gather barometric pressure and·humidity readings.· Any suggestions?

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Showing up to school doesn't·mean you are a student any more than crawling up in an oven means that·you are a biscuit.

John Kauffman

There are humidty detectors out there that output in BCD. Mine cost about $25 fifteen years ago.

Humidity:
hang a cluster of 5 to 20 hairs (human, horse) about 20-30 cm long
Hang a wieght of about 50-100 gm from the bottom.
Connect weight to a long lever attached to the axle of a variable resistor.
Measure change in resistance as hair loosens/tightens with change in humidity > drops/raises weight > rotates lever > changes resistance.

Humidity alternate:
I have heard that a packed column of table salt crystals changes conductivity slightly with humidity. Should be easy & cheap to build in a glass tube and check out. Might also work by drying very salty water on a length of filter paper, hook up leads at each end and see if resistance changes with humidity.

Barometric:
Cap a 2 liter or so glass bottle with a tight latex diaphram (use thickest latex possible, surgiccal gloves or 'helium grade" balloon)
Glue end of lever to balloon
Lever mounts on axle of pot, then as above.
Change in pressure in atmos causes diaphram to rise/sink > changes height of lever > changes resistance

Barometric alternate:
Use or make a classic barometer with large sealed volume of air and an exit tube of liquid that rises and falls.
Use an opaque liquid like ink water.
Create an array of LEDs & photoresisters that check through many points of exit tube for transmission blocked by ink liquid.
Use STAMP to determine highest measure point which is blocked by indicator fluid.

Tracy Allen

There is information on the use of RCtime in the "applied sensors" curriculum from Parallax, free for download. Your student might take a look at that for some ideas, including a nice solar radiation measurement.

I have other weather sensor ideas on my web site at
www.emesystems.com/BS2index.htm

also, Matt Parnell's site is still up:
www.parnelleng.com/support/weatherstamp/

and Peter Anderson's site has a number of things relating to weather monitoring.
www.phanderson.com/stamp/wx_index.html

Don't necessarily restrict it to RCtime. These days there are more ways to capture data than ever (and it behooves students to have lots of tools in their kit!)

Another way to measure humidity is the wet bulb thermometer--since you can already do temperature. It does take maintenance.

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Tracy Allen
www.emesystems.com