Tag Archive | "arduino tutorials"

Moving Forward with Arduino – Chapter 14 – XBee introduction

Learn how to use XBee wireless data transceivers with Arduino. This is part of a series originally titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Updated 02/03/2013

We will examine the Series 1 XBee wireless data transceivers from Digi in the USA. Although in the past we have experimented with the inexpensive 315MHz transmit/receive pair modules (chapter 11), they have been somewhat low in range and slow with data transmission. The XBee system changes this for the better.

First of all, what is an Xbee module? It is a very small piece of hardware that can connect wirelessly with another using the Zigbee communication protocols. There are many different models, including aerial types and power outputs. In this tutorial we’re using Series One XBees.

From Wikipedia, Zigbee is:

ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on the IEEE 802.15.4-2003 standard for wireless home area networks (WHANs), such as wireless light switches with lamps, electrical meters with in-home-displays, consumer electronics equipment via short-range radio. The technology defined by the ZigBee specification is intended to be simpler and less expensive than other WPANs, such as Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low data rate, long battery life, and secure networking.

Phew. For this chapter I will try and keep things as simple as possible to start off with. Here is an image of a typical Xbee unit:

Note that the pin spacing is small than 2.54mm, so you cannot just drop these into a breadboard. However for the purposes of our experimenting more equipment is needed. Therefore I am making use of this retail package from Sparkfun:

xbeeretailpackopenedsmall

This bundle includes two Xbee modules, an Xbee shield to connect one of the modules to an Arduino Uno-style board. When it comes time to solder the sockets into your shield, the best way is to insert them into another shield that is upside down, then drop the new shield on top and solder. For example:

solder2s

Finally, the bundle also includes a USB Explorer board, which allows us to connect one Xbee to a personal computer. This allows us to display serial data received by the Xbee using terminal software on the PC. One can also adjust certain Xbee hardware parameters by using the explorer board such software.

Let’s do that now. You will need some terminal software loaded on your computer. For example, Hyperterminal or Realterm. Plug an Xbee into the explorer board, and that into your PC via a USB cable. Determine which port (for example COM2:) it is using with your operating system, then create a new terminal connection. Set he connection to 9600 speed, 8 bits, no parity, 1 stop bit and hardware flow control. For example, in Hyperterminal this would look like:

Once you have established the connection, press “+++” (that is, plus three times, don’t press enter) and wait. The terminal screen should display “OK”. This means you are in the XBee configuration mode, where we can check the settings and change some parameters of the module. Enter “ATID” and press enter. The terminal window should display a four-digit number, which is the network ID of the module. It should be set by default to 3332. Unless you plan on creating a huge mesh network anytime soon, leave it be. To be sure your modules will talk to each other, repeat this process with your other XBee and make sure it also returns 3332. However as this is the default value, they should be fine.

Now for our first example of data transmission, insert one Xbee into the explorer module, and the other into the Xbee shield. With regards to the Xbee shield – whenever it is connected to an Arduino board and you about to upload a sketch, look for a tiny switch and change it to DLINE from UART. Don’t forget to change it back after uploading the sketch. See:

shieldswitchss

We are going to use the two Xbee modules as a straight, one-way serial line. That is, send some data out of the TX pin on the transmit board, and receive it into the terminal on the PC. Now upload this sketch into your Arduino board. This is a simple sketch, it just sends numbers out via the serial output. Then set the switch on the shield back to UART, and reset the board. If you can, run this board on external power and put it away from the desk, to give you the feeling that this is working 🙂

Note: More often that not one can purchase AC plug packs that have USB sockets in them, for charging fruity music players, and so on.

acusbss

Or you might have received one as a mobile phone charger. These are great for powering Arduino boards without using a PC. Now ensure your explorer module is plugged in, and use the terminal software to connect to the port the explorer is plugged into. After connecting, you should be presented with a scrolling list of numbers from 0 to 99, as per example 14.1 sketch:

numbers

How did you go? Sometimes I used to get the COM: ports mixed up on the PC, so that is something to keep track of. If you are powering both Xbees from your PC using USB cables, double-check the terminal software is looking at the explorer board, as an Arduino transmitting serial data through an Xbee shield will still send the same data back to the PC via USB.

Now that we have sent data in one direction, we can start to harness the true power of Xbees – they are transceivers, i.e. send and receive data. Next, we’ll create an on-demand temperature and light-level sensor. Our arduino board will have a temperature sensor and a light-dependent resistor, and using the terminal on the computer, we can request a temperature or light-level reading from the remote board. More about temperature sensors in chapter two. First of all, the remote board hardware setup:

exam14p2boardss

… and the schematic:

exam14p2schemss

 

It never hurts to elevate your other Xbee:

xbeewallss

For the PC side of things, use the explorer board and USB cable. Here is the sketch. It is quite simple. The remote board ‘listens’ to its serial in line. If it receives a “1”, it reads the temperature, converts it to Celsius and Fahrenheit, and writes the result to its serial out line, which is sent over our Xbee data bridge and received by the host computer. A “2” will result in the analogue value of the photocell to be sent back as a “light level”. Once again we use the terminal software to control the system.  Here is a quick video of the terminal in action:

The speed is quite good, almost instantaneous. By now hopefully you can see how easy it is to end some data backwards and forwards over the ether. The range is only limited by the obstacles between the Xbee transceivers and the particular power output of each model. With example 14.2, there were two double-brick walls between them. Furthermore, we can build fully computer-independent systems that can talk to each other, such as more portable remote controls, or other data-gathering systems. In the next few chapters, sooner rather than later.

LEDborder

Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, learning electronics, lesson, microcontrollers, RTL-11445, tutorial, wireless, WRL-09819, WRL-11215, xbeeComments (9)

Blinky the one-eyed clock

In this tutorial you learn how to make a blinking clock with a difference!

Updated 18/03/2013

Followers of my website would realise that I tend to make too many clocks in those tutorials. Well, I like making clocks… so here is another one. However this time I have tried to make the most simple version possible. Usually projects will have many LEDs, or perhaps an LCD, buzzers, buttons, all sorts of things. Which looks great and will impress many. But the other day I thought to myself … “how few things do you need to show the time?”

So here is my answer to that question: Blinky the one-eyed clock …

workingsss

It reminds me of the giant killer orb from The Prisoner… Using a minimal Arduino bootloader system, a DS1307 real time clock IC and an RGB diffused LED … we can make a clock that blinks the time, using the colours of the LED to note different numerical values. For example, if the time is 12:45, the clock will blink red 12 times, then show blue for a second (think of this as the colon on a digital clock) then blink four times in green (for forty minutes), then blink three times in red for the individual minutes. If there is a zero, blink blue quickly. Then the clock will not display anything for around forty seconds, then repeat the process. Here he (she, it?) is blinking the time:

Setting the clock is simple. It is set to start at 12:00 upon power up. So for the first use you have to wait until about five seconds before midday or midnight, then power it up. To save cost it doesn’t use a backup lithium battery on the real-time clock IC, but you could if you really wanted to. If you would like to follow my design process narrative, please read on. If you only want the sketch and schematic, 🙁 head to the bottom of this article.

Design process narrative…

So let’s get started!

The first thing to do was test the RGB LED for brightness levels, so I just connected it to the digital output pins of my Eleven via suitable current-limiting resistors. Each LED is going to be different, so to ensure maximum brightness without causing any damage you need to calculate the appropriate resistor values. This is quite easy, the formula is: resistor (ohms) = voltage drop / LED current So if you have a 5 V supply, and LED that needs only 2 volts, and draws 20 milliamps (0.2 amps) , the calculation will be: resistor = (5-2)/0.02 = 150 ohms. To be safe I used a 180 ohm resistor. The LED was tested with this simple sketch:

It was interesting to alter the value of d, the delay variable, to get an idea for an appropriate blinking speed. Originally the plan was to have the LED in a photo frame, but it was decided to mount a ping-pong ball over the LED for a retro-style look.  Here is a short video of the result of the test:

If you are going to use a ping-pong ball, please be careful when cutting into it with a knife, initially it may require a lot of force, but once the knife cuts through it does so very quickly:

cuttingppballss

Now it was time to develop the sketch to convert time into blinks. The sketch itself is quite simple. Read the hours and minutes from the DS1307 timer IC; convert the hours to 12 hour time; then blink an LED for the number of hours, display another colour for the colon; divide the minutes by ten and blink that in another colour; then the modulus of minutes and ten to find the individual minutes, and blink those out. Here is the first sketch I came up with. Finally, the code was tested using the Eleven board and my DS1307 real time clock shield. It is best to use existing hardware while testing, before committing to purchasing new hardware and so on. So here it is on the breadboard:

workingprototype1ss

And telling the time! In this example, the time is 3:45…

But perhaps that was a little bland. By using analogWrite() we can control the brightness of the LED segments. So now there are two more functions, whiteGlow() and blueGlow(); whose purpose is to make the display “glow” by increasing then decreasing the brightness. And scale back the amount of blinking, to increase battery life and make blinky less obvious. So now the display will glow white to announce the forthcoming display of time, wait a second, blink the time (with a blue glowing colon) then stay dark for ten seconds before repeating the process. Here is a quick demonstration of this display style:

Here is the sketch for the above demonstration, and the final one I will use with the hardware prototype. Once happy with the sketch, I put a fresh ATmega328 with Arduino bootloader in the board and programmed it with the blinky sketch, to be used in the final product.

Next was to build my own hardware. My last hardware unknown is the amount of current the circuit draws. Once I know this the correct voltage regulator and power supply can be decided upon. I had a fair idea it would be less than 100 milliamps, so I put a 6V battery onto supply duty via a 78L05 5V regulator (data sheet), and recorded the result:

So it varies, between 20.5 and 46 mA. As it only reaches 46 mA for a short time, we could consider the constant draw to be averaged out at 30 mA. I really want this to be able to run from a battery, but without having an external lead-acid battery lurking around, it will need a plug-pack with an output voltage greater than 7V DC. Another alternative would be to run it from a USB socket, a nice source of 5V. If doing so, there wouldn’t be a need for the 78L05 regulator. Which brings us to the  circuit diagram, which includes the power regulator:

blinkyschematicss

 

It does not allow for programming in the circuit, so you will need to program the microcontroller on another Arduino or compatible board, then transfer it to the blinky circuit board as described above. At this stage I tested it again, but using a solderless breadboard. In doing so you can make final hardware checks, and  generally make sure everything works as it should. This is also a good stage to double-check you are happy with the display behaviour, default time and so on.

breadboardedss

Time to solder up the circuit on some stripboard. Blank stripboard varies, but luckily I found this and a nice box to hold it in:

boxandpcbss

Stripboard does vary between retailers and so on, so you will need to work out the layout with your own board. In doing so, please double-check your work – follow the layout against the schematic and so on. Have a break, then check it again. There is nothing worse than soldering away to realise you are one strip too far over or something. My hand-eye coordination is not the best, therefore my soldering isn’t pretty, but it works:

solderedfrontss

 

solderedrearss

One would say that there is a good argument for making your own PCBs… and I would start to agree with that. The LED is soldered to some short leads to give it a bit of play, and some heatshrink over the legs to keep them isolated:

heatshrinkledss

 

And finally, to add a DC socket to feed blinky some power…

finalbaress

 

The last thing was to check the soldering once more under natural light, to check for bridges or shorts, then have a cup of tea. Upon my return I drilled out a hole in the enclosure lid for the LED, and one one the side for the DC socket, and fitted the lot together… and success! It worked 🙂

So there you have it. The journey from a daydream to a finished product… well a prototype anyway. But it works, and that is the best feeling of all. You can download the schematic from here. And here is the Arduino sketch:

I hope you enjoyed reading this post and hopefully felt inspired enough to make your own.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, clocks, ds1307, microcontrollers, projects, RGB LED, tutorialComments (18)


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