June 19th, 2009

Measuring Wind Speed

Measuring Wind Speed

The are a few ways to measure wind speed, some involving ultrasound transducers, some based on cooling effect of air flow but most common technique uses  spinning cups and measures their rotation speed. There are also a few ways to measure this rotation, some using a dynamo, some using Hall sensors but most use a photo-interrupter in a way much like it’s found in a computer mouse for example.

This kind of anemometer is presented in this project. Four hemispherical cups are attached to a rotating axis. At the other end of the axis there is a disc with  4 slits. Holes can also be used if they’re close enough to the edge. This disc’s slits or holes go in the photo-interrupter gap. Now when wind blows in the cups and spins the axis, the photo-interrupter will output a series of pulses whose period depends on the speed of rotation. Now you can either measure frequency, number of pulses within a time unit or the mean voltage of these pulses.

Note that the greater number the whole or slits are done in the disc the greater the resolution will be. The diameter of the disc is also an important factor in resolution.

The rotation speed is measured in this project by a PIC16F873 microcontroller. The photo-transistor has its collector connected to Port A0 from the PIC. The developer of the project is planning to display the measurement result on a screen but he also made an USB interface to send the data to PC. USBN9604 IC is used for this task. The article recommends that you ground the parallel input pins if not used so that it won’t cause interference.

The project right now is a work in progress but the principles of its operation have been stated. Also a schematic is provided and the circuit explanation. I for one, am waiting for complete article to check out the measurement algorithm.

Measuring Wind Speed: [Link]

May 27th, 2009

Weather Indicator

Weather Indicator

Not all of us understand weather mechanisms, how storms develop or what a low pressure front means so having a weather station that measures these parameters and display them as numbers might not be that helpful. However a team from Cornell University designed and built a station that displays a graphic representation of the current weather condition. If its stormy outside you will see a cloud with some raindrops and a lightning, all this on a 88 RGB LED matrix.

There are two main modules making this station. The outdoor module who makes all the measurements and then sends the data wirelessly to the indoor module which will display the icon corresponding to the data received. The data transmission is done on  433Mhz  by two Linx Technologies modules models RXD-433-KH2 and TXD-433-KH2. These modules also take care of data encoding and decoding using an address code so that only your specified modules will receive the transmission.

The outside station has five sensors to measure weather parameters. A solar cell, which also provides power, measures the light intensity and so it can tell if it’s day or night, cloudy or sunny. A LM34 is used as the temperature sensor and outputs a 10mV with every degree F. Rain sensor is from a Hot Wheels Radar Gun, using a Doppler Radar operating at 10.525GHz is sensitive enough to measure velocity of rain drops. A Diy anemometer was the choice as wind speed measurement tool and a capacitor who changes capacitance based on humidity is used for the last measurement.

ATmega644 is the microcontroller gathering data from all the sensors. This is then transmitted as a 10 bits code, each sensor data having  2 bits in that message. Inside the indoor module we find another ATmega644 who controls the LED matrix. Using PWM to drive the LEDs a very high number of colors is achieved instead of the usual 8 colors.

This project offers a large amount of information and insight into weather monitoring systems. It will require some skills to built it, specially the anemometer, it not as easy as it looks but it’s worth it.

Weather Indicator: [Link][Via]

July 8th, 2008

Windmeter / Anemometer

Windmeter / Anemometer

The Windmeter is an anemometer designed to measure and record wind speed distribution from 0 to 17+ meters per second. It was designed for high reliability, ease of construction, and for a wide environmental range. Data is logged over a period of 30.46 days (1/12 of a year), and then saved for 11 months. The data can be retrieved with a laptop computer any time within the 12 months of logging. The Windmeter is self-powered by a solar pannel and battery. Calibration of the Windmeter can be done against a car’s speedometer or better yet a GPS receiver. The Windmeter should cost you under $300 Can. to make.

Windmeter / Anemometer: [Link]

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