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Project Anemometer
Combining mechanics and electronics to study the wind.

There are different kinds of anemometers and different uses for them. Meteorology, Physics, Aviation, Engineering, Climatology are fileds of study that use anemometers to study the wind and apply the metrics for a specific purpose.

This tutorial outlines building a mechanical anemometer using 3D printed parts, a microcontroller, LED, and photoresistor.

Learn about:

  • Wind
  • Anemometers
  • Microcontrollers
  • Photoresistors
  • Circuits
  • Iterative Design

Let's learn! Let's build!

Anemometer System

Weather apps and meteorological reports generally indicate a wind speed for a widespread area. As an example, the weather report might estimate gusts within a city boundary or near a landmark such the ocean or river. An anemometer, on the other hand, estimates wind speed at the location that the anemometer is placed. Localized wind measurements can indicate wind speed in a backyard or an approved model rocket launch site.

Anemometers are a system of sub-systems. Each sub-system performs a specific function with the end result estimating wind speed.

The Computer Aided Design (CAD) render below illustrates the Anemometer as full system in the design and development stage. CAD guides an iterative build process by designing each sub-system and calculating the alignment of each sub-system before parts manufacturing and assembly. CAD also helps reduce material waste caused by a trial and error approach to design because the dimension of the parts is more accurate.

Here's a break down of the anemometer as a whole from top to bottom:

  Cups
Wind exerts force on the Cups which rotate the Light Chopper at the end of the Center Studding interrupting light between the Light Emitting Diode and Photoresistor. The Cups are hemispherical and hollow on one side. Studies have shown that anemometers with three cups generate consistent torque, respond to wind easily and spin when the wind blows in any direction.
  Bearings
The Bearings help reduce friction between the Center Studding and the material used to house the Center Studding (also called the Bearing Case in the design for this anemometer). This anemometer uses mechanical ball bearings, one at the top and bottom of the bearing case. Minimized friction from the bearing acts as a sub-system helping the Cups revolve around the Center Studding more easily.
  Cup Arms
The Cups are mounted to the Cup Arms. The Cup Arms are locked to the Center Studding and work together as a unit to turn the Center Studding and Light Chopper. Since a circle is 360 degrees and there are three Cup Arms, the Cups are at 360 / 3 = 120 degrees from one another. The even spacing allows the Cups to turn in any direction based on the direction of the wind.
  Photoresistor
The Photoresistor is one of the electrical components used as the "brain" of the anemometer. The resistance of the Photoresistor changes based on the amount of light exposed to it. Resistance decreases when the exposed light increases, and the resistance increases as the exposed light decreases. The change in resistance is detected by the microcontroller.
  Light Emitting Diode
A Light Emitting Diode is a semi-conducting device that emits light when current is past through it. This anemometer uses a red Light Emitting Diode aimed at the Photoresistor at a constant brightness. The Light Chopper placed between the Light Emitting Diode and Photoresistor interrupts the red light causing the resistance in the Photoresistor to change. This change in resistance correlates to wind speed.
  Light Chopper
The Light Chopper is a cylindrical shape that has blades spinning between the LED and Photoresistor. As a fin from the Light Chopper passes between the Photoresistor and Light Emitting Diode it interrupts the red light causing the resistance to fluctuate. The changing light condition causes an oscillating electrical signal which is calibrated at the Microcontroller to convert the oscillations to wind speed.
  Microcontroller
Microcontrollers are Integrated Circuits (mini computers) that are designed to perform a specific task. In the case of this mechanical anemometer, the Microcontroller reads the changing resistance from the Photoresistor then converts the analog/oscillating curve to a digital "on/off" type curve. The frequency of "on/off" changes correlate to the wind speed.
  Bolts, Nuts, Washers
The Bolts, Nuts, and Washers are hardware components used to hold all the other parts together. Specifically important are the jamming nuts that hold the Cup Arms and Light Chopper on the Center Studding. Torque acting on the Center Studding as it spins can cause the nuts to loosen unless they are jammed.
The above section introduces the Anemometer as a full system and loosely describes each sub-system. To fully understand the inner workings of the Anemometer let's take a look at the sub-systems in a little more detail. There are three main sub-systems:
 Structural
 Mechanical
 Electrical
Anemometer Cups

The Cups are an interesting part because they can be either structural or mechanical. Although the Cups are affixed to a structural part (Cup Arm) the Cup itself is experiencing acceleration from the wind force. Thus, for this design the Cups are a member of the mechanical sub-systems.

The animated CAD drawing shows the Cups attached to the Structural Cup Mount and Cup Arms but the entire part revolves due to the force on the cups making them a static machanical part.
Ball Bearings

Ball Bearings reduce rotational friction and radial load on the Center Studding as the wind forces the Anemometer Cups to turn.

Ball bearings consist of several components but the bearings in the anemometer have four to consider:
 Outer Race
The Outer Race is the outer ring of the bearing. Given the bearing is pressed into the bearing case the Outer Race will be stationary.
 Inner Race
The Inner Race is the inner ring of the bearing and rotates freely with the Center Studding.
 Ball Cage
The Ball Cage sits between the Outer Race and Inner Race and contains the bearing balls so that they are evenly spaced and handle the radial load effectively.
 Balls
The Balls revolve around the Inner Race which minimize friction as the Inner Race turns at the same rate as the Center Studding.
Light Chopper
The Light Chopper is fixed to the Center Studding and rotates at the same rate as the Anemometer Cups.
The Light Chopper itself is mechnical but it directly interfaces with the Light Emitting Diode (LED) and Photoresistor. The mechanical rotation of the blades interrupt the red light shining on the Photoresistor from the LED.
The radius of the Light Chopper is 20 mm which allows for 8 distinct blades positioned around the center of the cylinder that comprises the Light Chopper. Since there are 8 blades, the Photoresistor is blocked 8 times per 360 degrees revolution. These light interrupts translate to 8 digital pulses or 8 high/low states which are converted by the Microcontroller into wind speed after some calibration.
The animated CAD render of the Light Chopper illustrates how the revolution of the blades interrupts the light beam aimed at the Photoresistor.
Microcontroller
The Light Chopper is fixed to the Center Studding and rotates at the same rate as the Anemometer Cups.
The Light Chopper itself is mechnical but it directly interfaces with the Light Emitting Diode (LED) and Photoresistor. The mechanical rotation of the blades interrupt the red light shining on the Photoresistor from the LED.
The radius of the Light Chopper is 20 mm which allows for 8 distinct blades positioned around the center of the cylinder that comprises the Light Chopper. Since there are 8 blades, the Photoresistor is blocked 8 times per 360 degrees revolution. These light interrupts translate to 8 digital pulses or 8 high/low states which are converted by the Microcontroller into wind speed after some calibration.
The animated CAD render of the Light Chopper illustrates how the revolution of the blades interrupts the light beam aimed at the Photoresistor.
Red Light Emitting Diode (LED)
The Light Chopper is fixed to the Center Studding and rotates at the same rate as the Anemometer Cups.
The Light Chopper itself is mechnical but it directly interfaces with the Light Emitting Diode (LED) and Photoresistor. The mechanical rotation of the blades interrupt the red light shining on the Photoresistor from the LED.
The radius of the Light Chopper is 20 mm which allows for 8 distinct blades positioned around the center of the cylinder that comprises the Light Chopper. Since there are 8 blades, the Photoresistor is blocked 8 times per 360 degrees revolution. These light interrupts translate to 8 digital pulses or 8 high/low states which are converted by the Microcontroller into wind speed after some calibration.
The animated CAD render of the Light Chopper illustrates how the revolution of the blades interrupts the light beam aimed at the Photoresistor.
Photoresistor
The Light Chopper is fixed to the Center Studding and rotates at the same rate as the Anemometer Cups.
The Light Chopper itself is mechnical but it directly interfaces with the Light Emitting Diode (LED) and Photoresistor. The mechanical rotation of the blades interrupt the red light shining on the Photoresistor from the LED.
The radius of the Light Chopper is 20 mm which allows for 8 distinct blades positioned around the center of the cylinder that comprises the Light Chopper. Since there are 8 blades, the Photoresistor is blocked 8 times per 360 degrees revolution. These light interrupts translate to 8 digital pulses or 8 high/low states which are converted by the Microcontroller into wind speed after some calibration.
The animated CAD render of the Light Chopper illustrates how the revolution of the blades interrupts the light beam aimed at the Photoresistor.