Arduino data logger (data acquisition system)
The data logger, or data acquisition system, was made to try to get more information about the performance of the wind turbines I
have been making. While the wind speed and output power could be read from meters it was nearly
impossible to store the constantly changing data.
The information I was hoping to collect would allow me to determine the efficiency of a wind turbine
and compare different designs. The turbines were being used to directly charge
a battery so the information I was interested in is:
- The output voltage. This would be approximately the voltage of the battery being charged.
- The charging current. This combined with the voltage gives the power output of the turbine
and generator combination. If the resistance of the generator coils and wiring is known it can
also be used to estimate the input power of the wind turbine.
- The wind speed. This gives the power available to a wind turbine if the swept area is known.
Combining this with the output and input power of the generator from the current and voltage measurements
the efficiency of the turbine, and overall efficiency can be found.
- The rotational speed of the turbine. This can be found from the frequency of the AC current from the generator
and then adjusted to take into account the number of magnets in the generator. From this the tip speed ratio of the
turbine can be calculated.
The diagram illustrates the measurement points.
This was my first attempt at designing electronic circuits and started with a lot of research on the web.
The Arduino open source processor board has
been used by people doing similar projects and with its multiple ADC and digital inputs and a USB connection
to a PC seemed a good starting point. A new Arduino Mega 2560 from ebay cost £25.00(UK) and
proved to be quite easy to programme with good documentation. The
Arduino board does not contain any permanent data storage, although it is possible to connect an
SD card with suitable adapters, so I intended to use the board connected to a laptop and stream the
data into a file on the laptop hard drive.
The Arduino's ADC and digital ports are based on a 0 to 5V input range. The next problem was to
take the measurement points in the diagram above and turn them into a signal suitable to be
read by the Arduino. I don't claim any great experience of electronics so there may be better ways of
doing this but the route taken seems to work.