My blog was down for a few days. The hosting svc had to consolidate its IP blocks and give some back to the RAR, so my rustybolt.info was pointing to the wrong IP.
I was looking out the patio door at the radiometer on the table outside, watching it spinning like crazy in the really bright sunlight we’ve had for a few days, and the thought occurred to me. Why not put a led pointed at the blades and count the pulse rate? The more light, the faster it spins. But at low light levels, sunset and sunrise, it doesn’t spin, so it can’t measure the light level.
The guys I correspond with homebrew their own thermometer and barometer with an Arduino. They add pressure and temperature sensors, a LCD, and the software, and they have a working thermometer and barometer. But a few years ago I bought several indoor/outdoor thermometers for a very low price from a surplus store, and they work OK as long as I put new button cells in them every year. And the barometric pressure isn’t that important. I’m really more interested in the wind speed and direction. And as I said, the insolation (solar radiation). The weather is pretty boring here, it hardly ever freezes, the temperature just gets down to 50 to 60 degrees at night and high 80s most of the year, except for a few weeks during the summer and winter, and it’s a desert, there has been so little rain. My gauge of how windy it is is to look out the window and see if the palm trees are bending. If it’s really gusty, I can see the water in the toilet bowl moving up and down as the gusts blow across the vent pipe on the roof.
I thought about the radiometer, and realized that all I really need is a solar cell and a small piece of glass that goes in a welding helmet, to cut the light down to let the cell operate in its linear range. Point them up to the sky and measure the cell resistance with the Arduino. Calibrate it with a light meter. The measurements can be spaced every few minutes, since the sunlight doesn’t change fast except during a storm.
Okay, now for the wind speed and direction. I looked at the anemometer wiki and I was overwhelmed by more than a dozen different ways to measure the wind speed. I’m guessing that eight directions of 45 degrees each would be good enough, or else 16 at 22.5 degrees each. The wind speed and direction change more rapidly, so they may have to be measured every few seconds or less.
So there are 5 things to measure. Pressure, temperature, radiation, wind speed, wind direction. A CMOS 4051 can multiplex analog signals onto a common input. Or does an Arduino already have enough inputs of the right kind to do the job.
Another consideration is adding a logging feature. Store the measurements and their date+time in a file, formatted for processing at a later time.
I looked at models sold commercially. They can be bought for $50.00 or less from Walmart and Fry’s. Some have a precipitation gauge, but like I said, it seldom rains here. Some cities or municipalities have most of the info on their website. About the only thing I can’t get online is insolation, and that’s easy to obtain with the photocell.
