Anemometer & Wind Direction circuit

A project log for Climate & Environment Monitoring Station

Create a monitoring station to measure weather, soil, seismic, solar, magnetic, and gravity conditions - focus best accuracy/dollar w/COTS.

sparks.ronsparks.ron 01/14/2019 at 21:100 Comments

It has been several decades since I did a complicated Karnaugh Map to lay out a digital circuit. Which means it took a lot of time and review to get the knowledge brought back to the front of my memory and skill stack.  Anyway, the concept for the circuit was deceptively simple.  The way the sensor works it it has two magnets and two reed switches. One sensor physically aligned with north for the wind speed rotor and one for the direction vane.  The number of counts per minute of the rotor vane is a representation of the wind speed.  The wind rotor also has a magnetic shield that extends up into the direction vane.  This means the direction switch will close once each revolution when the rotor aligns with the direction.  The time difference between the two closures is therefore the proportion of the circle between north and the direction vane. Clever and patented.

The beauty of this approach is the significant resolution improvement over more traditional multi-switch direction sensors or drag and friction in potentiometer sensors.  It allows the entire assembly to be completely sealed from the elements and corrosion.

The circuit to use the Peet style anemometer needs to respond quickly, since at high wind speeds and directions near to north, the time between pulses can be very short.  In order to get the resolution I wanted, it was too short for an Arduino. It would likely work on the faster MCUs like the ESP series.  However, that still would not resolve any variability in processing timing to count the time. So I decided on simple "jelly bean" digital logic as an inexpensive and reasonably stable timing platform.

I have attached my prototype circuit (done in Logisim-Evolution) and it will be the basis for the first breadboard circuit.  Once I have gone through the necessary datasheets and part selection I will include those parts in the list and do a Kicad schematic.