Forget the seaweed and the proverbs, and let technology cater for your insatiable interest in the weather!

The EPE Met Office of December ’95 and January ’96 was the last Weather Centre to be published in these pages. A lot of water has passed under many bridges since then, in more ways one! One flood has been in the way that readers have taken to PIC microcontrollers during that period.

As long as three years ago we recognised that the time was ripe to publish another Weather Centre, this time using a PIC16F877 and its ready capability of monitoring many types of sensor simultaneously. It was also obvious that this device could easily be used in conjunction with serial memory chips, to perform long-term data recording for subsequent download to a PC-compatible computer for analysis.

The technique for such recording had already been proved in the author’s PIC 8-Channel Data Logger (Aug/Sep ’99). There was a problem, though. It lay not so much in the basic monitoring and logging, as with the author! He had rashly said that the next weather centre he did should be entirely solid state – no moving parts whatsoever.

As most of you will know, traditionally a weather centre has always had two moving parts, an anemometer for measuring wind speed, and a vane that indicates the direction from which it blows. For readers (and the author), for whom electronics is the chosen technological path to be passionate about, mechanics is the weakest link – goodbye to all that, seemed to be the prevailing thought.

So, the reasoning was that electronics by now should be capable of sensing wind speed and direction without resorting to rotational mechanics. There were many ideas of how it might be done, but no practical experiments had been performed in Tech Ed’s garden. But, after much shilly-shallying and putting off the hard work, he’s done it now. As to how .. well all will be revealed in the article. But for our purposes here, let's take a look at the specifications as exactly what this PIC Met Office can do overall!

The PIC Met Office monitors a range of sensors and processes data for the following conditions:

• Barometric pressure, in millibars
• Temperature, in °C and °F, including sub-zero
• Atmospheric relative humidity, as an RH percentage
• Soil moisture, bone-dry to saturated, as a percentage
• Light intensity, as a relative percentage, full sun to total darkness
• Rain fall, immediate (is it raining now?)
• Rain fall, cumulative (by how much has the water barrel filled and over what period?)
• Wind speed, in kph, mph and Beaufort, immediate and averaged
• Wind direction, immediate and averaged, 0° to 360°
• Wind chill factor
• Rainbow alert!
• Recording of all data to non-volatile serial memory (up to 256 kilobytes)
• Selectable data sampling rates, from 1 second to 1 hour intervals
• Serial output (9600 baud) of realtime and recorded data to PC-compatible computer, running under Windows 95/98/ME
• Bargraph and waveform displays on PC
• Data formatted by PC for reading as text file compatible with Excel spreadsheet/ graphing software and text editors
• Immediate display of monitored sensor values via alphanumeric liquid crystal display