I have spent several nights already trying to get two Arduino boards, each equipped with an Xbee-shield, to communicate. I worked on the example provided on the Arduino site, but no luck It turned out that I obtained two shields with “Series 2″ radio’s, which meant the example code would not work right off the bat. But, a post on Didier Stevens’ website pointed me in the right direction and eventually I was able to get both boards running and communicating.

The two boards seem to be communicating as one is sending the signal to switch an LED on and off every second on the other board. I see the LED switching on and off, but the behaviour is quite erratic. So, more investigation to be done there…

To be continued…

If you want to follow the prototype on twitter, follow @ProjectG3H

There are some issues with the temperature readings as they spike to impossible levels every now and then. I will have to get into that later. But, for now the prototype is able to get environment data and connect to the internet to tell the world about them. And it was not a very hard thing to do. Very exciting!

I will do a thorough write-up later to share as much info as possible, but for now I am just so excited that this is actually sort of working, that I had to share!

Below is a little preview of the sensor data that is sent to pachube!

Temperature (in Celcius):

Light (value from the LDR):

Soil moisture level:

I also showed how to get a voltage reading instead of just a number. Today, I post a link to an article that accompanies Oomlout’s ARDX kit, about how to get an actual temperature from a temperature sensor.

Of course I could repeat all they say here and claim its my own, but as I learned it from using my ARDX kit, it is logical to point you to the source: http://www.oomlout.com/a/products/ardx/circ-10

Enjoy!

If you measure the voltage on the pin, you will find that it is anywhere between 0V and 5V, where 0V corresponds to the digital value 0 and 5V corresponds to 1024. This is not entirely true as the minimum voltage is 0.005V, or 5 millivolts.

That means that each step up, measured digitally (the range between 0 and 1024) corresponds to 5V/1024 steps = 0.0048828125V.

This can be easily put into a short function you can use for all sensors using a digital pin:

/*
* getVoltage() – return the voltage on the analoge input defined by pin
*
*/
float getVoltage(int pin) {
return (analogRead(pin) * .004882813);
// reading a digital pin returns a value between 0 and 1024, which corresponds to a voltage range
// between 0V and 5V.
// So, one digital step means 5V/1024 = ~0.005V, or about 5 millivolt
}

With this value it is a lot easier to translate the value read from the sensor to meaningful data. In a future post I will show you how to use a thermistor to measure temperature and use this information to translate the voltage on the digital pin to degrees centrigrade or fahrenheit.

To start the new year well in the tinkering department, I bought an Arduino! What’s that, you ask? Well, the Arduino website explains it thusly:

Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It’s intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.

Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on the board is programmed using the Arduino programming languageWiring) and the Arduino development environment (based on Processing). Arduino projects can be stand-alone or they can communicate with software on running on a computer (e.g. Flash, Processing, MaxMSP).

Arduino Duemilanove board

It has been around for a few years now, and I have always had an interest in programming microprocessors to allow devices, contraptions, etc to be functional independent of a PC. With Arduino, interfacing with the outside world is easier than ever which convinced me I should give it a try.

Since I live in the Netherlands, I looked for a resource in my country that provided Arduino’s. After looking through the list of suppliers in the Netherlands, I ended up buying from Floris.CC and ordere the “Arduino Experimentation Kit“, made by Oomlout and ordered from Floris.cc

Since receiving it, I played around with the thing a bit and what struck me most is the ease with which you can build contraptions that sense and act on their environment. In the next few weeks I will do a write up on the ARDX kit itself.

Playing (becaues that really is what it is!) with the Arduino is so much fun that it instantly sparks many creative ideas that this thing can help with. As those ideas are developed, I will do write-ups here to share the knowledge I gain.

If you want to know more about Arduino, get started with this PDFCast from Make Magazine, or watch these “Arduino 101″ video’s on YouTube.

Arduino Logo