Franklin Dattein

Summary
This project consists of the construction of an anemometer able to transmit the wind speed and direction over a GPRS network. The objective is to plug the cheapest cellphone and anemometer sensor into an Arduino.

Motivation
I have an on-line store to sell kitesurfing equipment and the most attractive page is the one that shows the wind speed for the main kitesurfing spots.
In addition, I have been playing with Arduino and remote device monitoring in the past few months just for fun and learning, so this project is pure fun and profit.

The problem
Weather monitoring is not an innovation. It is possible to buy a LaCrosse Weather Station for U$110,00 on Ebay. These stations are wireless and can be connected to a PC, which can easily transmit the wind speed through the web.
So, why do you want to build a new one from scratch?

For several reasons:

• Portability: A PC is too big to move and place on the top of a lamppost.
• Costs: A PC raises considerably (5+ times) the cost of the station.
• Connectivity: A regular internet connection is expensive and often unavailable in the most remote locations like lakes, rivers and beaches.

Alternative solutions

I have been studying some of the available alternatives, before starting to spend money on parts for this project. They can be divided three areas: the wind sensor, the cellphone interfacing and the Arduino interfacing.

The wind sensor

• I have spent a long time looking for an Anemometer Housing on the internet, without success. There are some cheap alternatives, but due to that size the shipping cost to Brazil is too expensive.
• Another thought was about buying a LaCrosse station and intercepting its RF signal with an Arduino RF receptor. Two disadvantages made me to put this idea on hold: 1. There is no documentation about the RF signal transmitted by the LaCrosse stations, so it would require reverse engineering, which is very complicated; 2. LaCrosse stations send their signals every 5 minutes, which is too slow for a $100 bucks sensor.
• There is a pretty good Anemometer sensor at Sparkfun web-site for U$69.95. It has an easy Arduino interfacing and a good coding library.  It’s Almost perfect for my purpose. Unfortunately, the shipping price is around U$40,00,  making a total of U$109,95, which can double if customs catch it.
• Do it yourself (DIY). It is possible to build one with around U$10,00 and some used parts. It is the cheapest option, but the disadvantage is obvious:  More labor.

By now I will focus on the last option.

Interfacing with the anemometer sensor
This problem might be easy or difficult to solve, depending on the sensor adopted.
The SparkFun and the DIY options can be easily interfaced with Arduino and a cable. The LaCrosse station would require a Arduino RF receptor and a lot of time reverse engineering its protocol.

Interfacing with the cellphone

That is the biggest problem, so far. There are too many variables involved like, usage of SMS or GPRS, the cheapest cellphone model, how connect arduino to the cellhpone pins and others.

SMS vs. GPRS: The data transmission over GPRS can be expensive, particularly in a country like Brazil where data plans are not so popular.
Sending data over SMS requires a complex SMS central receiver, built with another cellphone, integrated with a PC and internet. The data trasmission cost is cheaper compared to GPRS, but the required infrastructure is much more complex and expensive. It may be worth it, if there are several SMS clients communicating with the central receiver, but that is not my case.

At this moment I will try with the GPRS connection.

What is the best cellphone? The cheapest one!

A few years ago I took a look at my LowJack (GPS tracking system for Vehicles) and it had an old Motorola, which probably does not even support GPRS. After investigating a little more I found out that any cellphone with support for AT+ commands can be used for this.
After that I ended at sserial2mobile web page. It is an Arduino library to abstract the Motorola C168i At+ commands. This model can be found for around U$50,00 on Ebay, including the shipping to Brazil.

Alternatively, it would be very nice to have a GPRS shield easy to plug into Arduino. The cheapest one is not really cheap, it is again from SparkFun and its cost is around  U$100,00 plus shipping.

The solution
Currently the best solution seems to be the DIY anemometer sensor, an Arduino and a Motorola C168i.
I will be posting news about this project as soon as I have made some progress.