The Raspberry Pi is great at being anything Linux can be; The Arduino is not though- even though many people have tried.
Why am I using an Arduino then? Linux is not a real time operating system - It is event driven and processes
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The Arduino is very good at handling real time events like this. Thanks to that the wind speed will be precise- even at 100mph gusts. It can also handle analog signals that the Raspberry lacks. It is actually an Atmega168/328 that uses the Arduino boot loader- so i can use the Arudino IDE and all the libraries to help me handle these real time devices.It also has a full UART.
Time to choose
- What I have done is bought a Boarduino from ebay- ditched the voltage regulator and leach of the 3V3 from the Pi - The Atmega can run happily on that and best of all the UART will be at 3.3v - instead of the dreaded 5V that needs to be buffered. (In the breadboard i have a HCF4050 buffer - Because I thought I needed it, which I would have if it was powered at 5 Volts- So good riddance)
- I found the wyolum alamode and decided to buy that instead. It is designed to sit on top of the Raspberry Pi and has the same Arduino chip on it, with a buffer for protection and many pinouts. It is just easier to use. If you want, you can make your own for the fraction of the price using the boarduino approach.
I connected the Atmega UART to the Pi's GPIO UART and now I just need to do 4 things.
- Disable the ROOT Console that is redirected to that UART on the Pi
- Make a program/script in python(easiest i suppose??) that reads the UART
- Install basic php webserver that will read the python aka UART- make sense of the data. (possibly log to mysql) and output it as a JSON string. (later make it more complex)
- Connect the Pi to the Internet via WiFi (later even GPRS) - Insulate the Electronics somehow and put it outside in the harsh Brittish winds and rains. Leave it over winter- Lets see how long it lasts :)
am was will(arrgh) making my own breakout board for this that I will available for sale at a reasonable price. It will include the Atmega- loaded with the weather sketch, the RJ-11 connectors + extra - for Sparkfun's weather system. It will just plug on top of the Pi - It will not be programmable but using a Boarduino you can do what you want to it later...
To be continued ...