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Arduino Tutorials – Chapter 16 – Ethernet

Learn how to connect your Arduino to the outside world via Ethernet

This is chapter sixteen of our huge Arduino tutorial seriesUpdated 06/12/2013

In this chapter we will introduce and examine the use of Ethernet networking with Arduino over local networks and the greater Internet. It will be assumed that you have a basic understanding of computer networking, such as the knowledge of how to connect computers to a hub/router with RJ45 cables, what an IP and MAC address is, and so on. Furthermore, here is a good quick rundown about Ethernet.

Getting Started

You will need an Arduino Uno or compatible board with an Ethernet shield that uses the W5100 Ethernet controller IC (pretty much all of them):

Arduino Ethernet shield

…or consider using a Freetronics EtherTen – as it has everything all on the one board, plus some extras:

Freetronics EtherTen

Furthermore you will need to power the board via the external DC socket – the W5100 IC uses more current than the USB power can supply. A 9V 1A plug pack/wall wart will suffice. Finally it does get hot – so be careful not to touch the W5100 after extended use. In case you’re not sure – this is the W5100 IC:

Wiznet W5100

Once you have your Ethernet-enabled Arduino, and have the external power connected – it’s a good idea to check it all works. Open the Arduino IDE and selectFile > Examples > Ethernet > Webserver. This loads a simple sketch which will display data gathered from the analogue inputs on a web browser. However don’t upload it yet, it needs a slight modification.

You need to specify the IP address of the Ethernet shield – which is done inside the sketch. This is simple, go to the line:

And alter it to match your own setup. For example, in my home the router’s IP address is, the printer is and all PCs are below …50. So I will set my shield IP to by altering the line to:

You also have the opportunity to change your MAC address. Each piece of networking equipment has a unique serial number to identify itself over a network, and this is normall hard-programmed into the equipments’ firmware. However with Arduino we can define the MAC address ourselves.

If you are running more than one Ethernet shield on your network, ensure they have different MAC addresses by altering the hexadecimal values in the line:

However if you only have one shield just leave it be. There may be the very, very, statistically rare chance of having a MAC address the same as your existing hardware, so that would be another time to change it.

Once you have made your alterations, save and upload the sketch. Now open a web browser and navigate to the IP address you entered in the sketch, and you should be presented with something similar to the following:

 Arduino webserver example sketch

What’s happening? The Arduino has been programmed to offer a simple web page with the values measured by the analogue inputs. You can refresh the browser to get updated values.

At this point – please note that the Ethernet shields use digital pins 10~13, so you can’t use those for anything else. Some Arduino Ethernet shields may also have a microSD card socket, which also uses another digital pin – so check with the documentation to find out which one.

Nevertheless, now that we can see the Ethernet shield is working we can move on to something more useful. Let’s dissect the previous example in a simple way, and see how we can distribute and display more interesting data over the network. For reference, all of the Ethernet-related functions are handled by the Ethernet Arduino library. If you examine the previous sketch we just used, the section that will be of interest is:

Hopefully this section of the sketch should be familiar – remember how we have used serial.print(); in the past when sending data to the serial monitor box? Well now we can do the same thing, but sending data from our Ethernet shield back to a web browser – on other words, a very basic type of web page.

However there is something you may or may not want to  learn in order to format the output in a readable format – HTML code. I am not a website developer (!) so will not delve into HTML too much.

However if you wish to serve up nicely formatted web pages with your Arduino and so on, here would be a good start. In the interests of simplicity, the following two functions will be the most useful:

Client.print (); allows us to send text or data back to the web page. It works in the same way as serial.print(), so nothing new there. You can also specify the data type in the same way as with serial.print(). Naturally you can also use it to send data back as well. The other useful line is:

which sends the HTML code back to the web browser telling it to start a new line. The part that actually causes the carriage return/new line is the <br /> which is an HTML code (or “tag”) for a new line. So if you are creating more elaborate web page displays, you can just insert other HTML tags in the client.print(); statement. If you want to learn more about HTML commands, here’s a good tutorial site. Finally – note that the sketch will only send the data when it has been requested, that is when it has received a request from the web browser.

Accessing your Arduino over the Internet

So far – so good. But what if you want to access your Arduino from outside the local network?

You will need a static IP address – that is, the IP address your internet service provider assigns to your connection needs to stay the same. If you don’t have a static IP, as long as you leave your modem/router permanently swiched on your IP shouldn’t change. However that isn’t an optimal solution.

If your ISP cannot offer you a static IP at all, you can still move forward with the project by using an organisation that offers a Dynamic DNS. These organisations offer you your own static IP host name (e.g. mojo.monkeynuts.com) instead of a number, keep track of your changing IP address and linking it to the new host name. From what I can gather, your modem needs to support (have an in-built client for…) these DDNS services. As an example, two companies are No-IP andDynDNS.com. Please note that I haven’t used those two, they are just offered as examples.

Now, to find your IP address… usually this can be found by logging into your router’s administration page – it is usually but could be different. Check with your supplier or ISP if they supplied the hardware. For this example, if I enter in a web browser, and after entering my modem administration password, the following screen is presented:

WAN IP address router

What you are looking for is your WAN IP address, as you can see in the image above. To keep the pranksters away, I have blacked out some of my address.

The next thing to do is turn on port-forwarding. This tells the router where to redirect incoming requests from the outside world. When the modem receives such a request, we want to send that request to the port number of our Ethernet shield. Using the:

function in our sketch has set the port number to 125. Each modem’s configuration screen will look different, but as an example here is one:

Arduino router port forwarding

So you can see from the line number one in the image above, the inbound port numbers have been set to 125, and the IP address of the Ethernet shield has been set to – the same as in the sketch.

After saving the settings, we’re all set. The external address of my Ethernet shield will be the WAN:125, so to access the Arduino I will type my WAN address with :125 at the end into the browser of the remote web device, which will contact the lonely Ethernet hardware back home.

Furthermore, you may need to alter your modem’s firewall settings, to allow the port 125 to be “open” to incoming requests. Please check your modem documentation for more information on how to do this.

Now from basically any Internet connected device in the free world, I can enter my WAN and port number into the URL field and receive the results. For example, from a phone when it is connected to the Internet via LTE mobile data:

Arduino webserver example cellular

So at this stage you can now display data on a simple web page created by your Arduino and access it from anywhere with unrestricted Internet access. With your previous Arduino knowledge (well, this is chapter sixteen) you can now use data from sensors or other parts of a sketch and display it for retrieval.

Displaying sensor data on a web page

As an example of displaying sensor data on a web page, let’s use an inexpensive and popular temperature and humidity sensor – the DHT22. You will need to install the DHT22 Arduino library which can be found on this page. If this is your first time with the DHT22, experiment with the example sketch that’s included with the library so you understand how it works.

Connect the DHT22 with the data pin to Arduino D2, Vin to the 5V pin and GND to … GND:

arduino ethernet freetronics etherten dht22 humid

Now for our sketch – to display the temperature and humidity on a web page. If you’re not up on HTML you can use online services such as this to generate the code, which you can then modify to use in the sketch.

In the example below, the temperature and humidity data from the DHT22 is served in a simple web page:

It is a modification of the IDE’s webserver example sketch that we used previously – with a few modifications. First, the webpage will automatically refresh every 30 seconds – this parameter is set in the line:

… and the custom HTML for our web page starts below the line:

You can then simply insert the required HTML inside client.print() functions to create the layout you need.

Finally – here’s an example screen shot of the example sketch at work:

arduino ethernet freetronics etherten dht22 humid cellular

You now have the framework to create your own web pages that can display various data processed with your Arduino.

Remote control your Arduino from afar

We have a separate tutorial on this topic, that uses the teleduino system.


So there you have it, another useful way to have your Arduino interact with the outside world. Stay tuned for upcoming Arduino tutorials by subscribing to the blog, RSS feed (top-right), twitter or joining our Google Group. And if you enjoyed the tutorial, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop” from No Starch Press.


Posted in arduino, DEV-09026, DEV-11230, DHT22, ethernet, internet, iot, shield, tronixstuff, tutorialComments (12)

Visualise microcontroller data with Megunolink Pro


When the time comes to capture data from a microcontroller-based project, or control an embedded project via a PC – the thought of writing the appropriate PC software can give some people a headache. Or if you’re an Arduino or other development board user and are frustrated with the Serial Monitor box – where do you go? These problems and many more can be solved by using the Megunolink Pro software that’s the subject of this review.

From the Megunolink website,

MegunoLink Pro is a tool designed to aid embedded electronics designers. MegunoLink provides a set of tools to help visualize serial data, it is made up of a set of visualizers that each have a unique function and any number of them can be utilized at once. With these visualizers and our functional tabbed and docked interface you can create a full control center for your embedded project. Plot, log and monitor serial streams from both hardwired, bluetooth, and network based (UDP) devices.

The user interface allows for a completely customized layout with many different visualisers displaying information at once. Perfect for developing exciting new microcontroller based designs. Data streams go from hard to follow serial messages to easy to interpret tables and interactive plots. The interface panel allows you to set up custom GUI elements that let you take control of your device from the comfort of your PC screen.

Phil from Megunolink gives us a quick demonstration in the following video:


Getting Megunolink running takes around ten minutes. You’ll need a recent PC running Windows of some variety (XP/ 2003/Vista/Win7/8) and also .NET Framework v4.0. You can download a trial Pro version which operates for seven days – at which point you can use the “lite” version or purchase a Pro license. The Megunolink team have given our readers a discount on the personal version, use the coupon code “TROMLP” for 30% off.


Using Megunolink is quite simple, even though there’s a whole pile of functions. From the home page there’s a variety of documentation for all of the software features, so you can get started very quickly. You can simply capture all output from the serial line and have it saved to a text file (and with a time/date stamp, which removes the need for a RTC in the hardware) – something which seems quite simple but not done with the Arduino IDE:


Furthermore there is an “upload monitor” in Megunolink – which can automatically disconnect from the COM: port used by an Arduino when you need to upload a new sketch, then reconnect afterward. This saves a lot of to-and-fro between the two programs when adjusting code.

The key to analysing data from the microcontroller is to insert text notes in the serial output, which are then interpreted by Megunolink for display purposes. For example, if you have your MCU code send labels with the data, Megunolink can then sort these out into channels and graph the data, for example:


An example Arduino sketch is provided to demonstrate this, and it translates to other development platforms. Another great feature is the ability to create a graphical user interface for projects connected to the PCB. You design the GUI which can include buttons, sliders and numeric fields, for example:


… and each of which send values of your choice to the device via USB. Then it’s a simple matter of coding your device to respond to the serial commands.

Real-time mapping

As mentioned in the video above, there’s also mapping support – your hardware sends GPS coordinates and they’re displayed in a real-time window:


Arduino programming

There’s also an interface to allow programming of an Arduino with .hex files via Megunolink. Currently it can work with the ATmega328, -2560, and with an external programmer -328P and -644 microcontrollers.


Once again Megunolink has proven to be a useful piece of software. It gives you a friendly and powerful connection to all the data from your microcontroller, and also a simple GUI for control via serial. So test it for yourself, it won’t cost you anything for the trial version. And if you like it – don’t forget about the tronixstuff.com discount on the personal version – use the coupon code “TROMLP” for 30% off. Finally, if you have any questions please contact Megunolink. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.

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.

[Note – Megunolink Pro software license was a promotional consideration]


Posted in arduino, data, data analysis, graphing, mapping, megunolink, review, software, software review, tronixstuffComments (2)

Interact with Arduino over the Internet with Teleduino


[Updated 06/12/2013]

Recently a new method of interacting with an Ethernet-enabled Arduino board and the Internet was brought to my attention – a new system called Teleduino. In this article we test a few of the basic features and see what is possible. Please note that these are my own experiments and that Teleduino is a work in progress. So follow along and see for yourself.

Getting Started

  1. You will need an Arduino Uno (or compatible) board and Ethernet shield with the Wiznet chip – or a Freetronics EtherTen (a much neater solution). Teleduino now supports Arduino Mega and the awesome EtherMega.
  2. Download and install the Teleduino Arduino library. This is available from the resources section of the home page. You will also need to be running Arduino IDE v1.0 or greater.
  3. Request an API key. This identified your particular Arduino from the rest.
  4. Get together some basic electronics components for testing, such as some LEDs and 560R resistors; sources of analog input such as an LDR or TMP36 temperature sensor; and a solderless breadboard.
  5. Don’t forget the Ethernet cable from your Arduino stack to the router!
  6. Finally, some rudimentary knowledge about networking will be useful. (IP address, DHCP, etc.)
The Teleduino system uses pin D8 for a status LED, so you may find connecting one up now useful while experimenting. Connect as such:

Controlling digital outputs

In this example we control an LED, turning it on and off. For demonstration purposes, connect another LED with a resistor to D6 in the same method as shown above. Next, you need to upload a sketch to the Arduino. It is the

which is included with the library examples. Before uploading, you need to make some modifications. The first of these is to add your API key. Go back to the email you received from Teleduino, and click on the link provided. It will take you to a website that shows a byte array variable named byte key[]. You will copy this into the sketch, replacing the same array full of hexadecimal zeros in the sketch – as shown below – with your own:

Next, scroll down to

… and change one of the hexadecimal numbers to 0x00… just in case there is a clash with other addresses on your network. You never know. Finally – depending on your network router, you may need to manually allocate the IP address for your Ethernet shield and/or set the DNS server to use. To do this, scroll down to

where you can change the useDHCP and/or useDNS variables to false, and update those values below. However if you’re not sure, just leave them be unless you need to change them. Finally – upload the sketch to your Arduino, get the hardware together and plug it into the network.

Watch your status LED – it will blink a number of times, depending on the status of things. The blink levels are:

  • 1 blink – initialising
  • 2 blinks – starting network connection
  • 3 blinks – connecting to the Teleduino server
  • 4 blinks – authentication successful
  • 5 blinks – session already exists for supplied key (sometimes happens after a quick restart – will work on next auto-restart)
  • 6 blinks – Invalid or unauthorised key – check your API key is correctly entered in the sketch as described earlier
  • 10 blinks – connection dropped

If all is well, after a minute yours should be on blink level 4, then it will idle back to blink level 1. Now to test the connection with our first command.

You send commands to the Arduino using a set of URLs that will contain various parameters. You will need your API key again for these URLs which is then inserted into the URL. The first will report the version of software on the Arduino. Send

however replace 999999 with your API key (and in all examples shown here). If successful, you should see something similar to the following in the web browser:

However if something is wrong, or there are connection difficulties you will see something like:

Before using digital outputs, and after every reset of the Arduino) you need to set the pin mode for the digital output to control. In our example, we use:

Note that the pin number and mode are set with single digits, as you can see above this is for pin 6, and we use mode=1 for output. You should save this as a bookmark to make life easer later on. When the command has been successfully sent, a message will be shown in the webpage, for example:

Moving forward – you turn the digital output on with the following:

and to turn it off, set the final part of the URL to

Easy. How did you go? It really is amazing to see it work. Now you can control your Arduino from almost anywhere in the world. Again, saving these as bookmarks to make things easier, or a URL shortening service.

At this point you should now have the gist of the Teleduino service and how it is operated.

There is so much more you can do, and currently the list includes (From the author):

  • Reset, ping, get version, get uptime, get free memory.
  • Define pin modes, set digital outputs, set analog outputs, read digital inputs, read analog inputs, or read all inputs with a single API call.
  • Define up to 2 ‘banks’ of shift registers. Each ‘bank’ can contain up to 32 cascaded shift registers, giving a total of 512 digital outputs.
  • Shift register outputs can be set, or merged, and expire times can be set on merges (you could set an output(s) high for X number of milliseconds).
  • Define, and read and write from serial port.
  • Read and write from EEPROM.
  • Define and position up to 6 servos.
  • Set preset values for the above functions, which get set during boot. Preset values are stored in the first 160ish bytes of the EEPROM.

[22/09/2012] New! You can also control the I2C bus – check out this tutorial for more information. For more information check the Teleduino web site, and further tutorials can be found here. Here is a simple example of Teleduino at work – controlling a light switch:


At this moment Teleduino is simple, works and makes a lot of ideas possible. We look forward to making more use of it in future projects, and hope you can as well. Kudos to Nathan Kennedy, and we look forward to seeing Teleduino advance and develop over the future. If all this Arduino is new to you, check out the tutorials.  Thanks to Freetronics for the use of their Ethernet-enabled hardware.

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, ethernet, internet, lesson, remote, teleduino, tutorialComments (10)

Tutorial: Maximising your Arduino’s I/O ports with MCP23017

This is chapter forty-one of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – a series of articles on the Arduino universe. The first chapter is here, the complete series is detailed here.

[Updated 04/12/2014]

In this article we discuss how to use the Microchip MCP23017 16-bit serial expander with I2C serial interface. This 28-pin IC offers sixteen inputs or outputs – and up to eight of the ICs can be used on one I2C bus… offering a maximum of 128 extra I/O ports. A few people may be thinking “Why not just get an Arduino Mega2560?” – a good question. However you may have a distance between the Arduino and the end-point of the I/O pins – so with these ICs you can run just four wires instead of a lot more; save board space with custom designs, and preserve precious digital I/O pins for other uses. Plus I think the I2C bus is underappreciated! So let’s get started…

Here is our subject of the article in DIP form:

At this point you should also download yourself a copy of data sheet – it will be referred to several times, and very useful for reference and further reading. Furthermore if you are not familiar with Arduino and the I2C bus, please familiarise yourself with the I2C tutorials parts one and two. The MCP23017 can be quite simple or complex to understand, so the goal of this article is to try and make it as simple as possible. After reading this you should have the knowledge and confidence to move forward with using a MCP23017.

First, let’s look at the hardware basics of this IC. Consider the pinouts:

The sixteen I/O ports are separated into two ‘ports’ – A (on the right) and B (on the left. Pin 9 connects to 5V, 10 to GND, 11 isn’t used, 12 is the I2C bus clock line (Arduino Uno/Duemilanove analogue pin 5, Mega pin  21), and 13 is the I2C bus data line (Arduino Uno/Duemailnove analogue pin 4, Mega pin 20). External pull-up resistors should be used on the I2C bus – in our examples we use 4.7k ohm values. Pin 14 is unused, and we won’t be looking at interrupts, so ignore pins 19 and 20. Pin 18 is the reset pin, which is normally high – therefore you ground it to reset the IC. So connect it to 5V!

Finally we have the three hardware address pins 15~17. These are used to determine the I2C bus address for the chip. If you connect them all to GND, the address is 0x20. If you have other devices with that address or need to use multiple MCP23017s, see figure 1-2 on page eight of the data sheet. You can alter the address by connecting a combination of pins 15~17 to 5V (1) or GND (0). For example, if you connect 15~17 all to 5V, the control byte becomes 0100111 in binary, or 0x27 in hexadecimal.

Next, here is a basic schematic illustrating how to connect an MCP23017 to a typical Arduino board. It contains the minimum to use the IC, without any sensors or components on the I/O pins:

Now to examine how to use the IC in our sketches.

As you should know by now most I2C devices have several registers that can be addressed. Each address holds one byte of data that determines various options. So before using we need to set whether each port is an input or an output. First, we’ll examine setting them as outputs. So to set port A to outputs, we use:

Then to set port B to outputs, we use:

So now we are in void loop()  or a function of your own creation and want to control some output pins. To control port A, we use:

To control port B, we use:

… replacing ?? with the binary or equivalent hexadecimal or decimal value to send to the register.

To calculate the required number, consider each I/O pin from 7 to 0 matches one bit of a binary number – 1 for on, 0 for off. So you can insert a binary number representing the status of each output pin. Or if binary does your head in, convert it to hexadecimal. Or a decimal number. So for example, you want pins 7 and 1 on. In binary that would be 10000010, in hexadecimal that is 0x82, or 130 decimal. (Using decimals is convenient if you want to display values from an incrementing value or function result).

If you had some LEDs via resistors connected to the outputs, you would have this as a result of sending 0x82:

For example, we want port A to be 11001100 and port B to be 10001000 – so we send the following (note we converted the binary values to decimal):

… with the results as such (port B on the left, port A on the right):

Now let’s put all of this output knowledge into a more detailed example. From a hardware perspective we are using a circuit as described above, with the addition of a 560 ohm resistor followed by an LED thence to ground from on each of the sixteen outputs. Here is the sketch:

And here is the example blinking away:

Although that may have seemed like a simple demonstration, it was created show how the outputs can be used. So now you know how to control the I/O pins set as outputs. Note that you can’t source more than 25 mA of current from each pin, so if switching higher current loads use a transistor and an external power supply and so on.

Now let’s turn the tables and work on using the I/O pins as digital inputs. The MCP23017 I/O pins default to input mode, so we just need to initiate the I2C bus. Then in the void loop() or other function all we do is set the address of the register to read and receive one byte of data.

For our next example, we have our basic sketch as described at the start of this article using four normally-open buttons (once again using the ‘button board‘) which are connected to port B inputs 0~3. Consider the first five lines of void loop() in the following example:

In this example void loop() sends the GPIOB address (0x13) to the IC. Then using Wire.requestFrom() it asks for one byte of data from the IC – the contents of the register at 0x13. This byte is stored in the variable inputs. Finally if inputs is greater than zero (i.e. a button has been pressed) the result is sent to the serial monitor window and displayed in binary. We display it in binary as this represents the state of the inputs 0~7. Here is an example of pressing the buttons 1, 2, 3 then 4 – three times:

And as we are reading eight inputs at once – you can detect multiple keypresses. The following is an example of doing just that:

As you can see pressing all four buttons returned 1111, or the first and third returned 101. Each combination of highs and lows on the inputs is a unique 8-bit number that can also be interpreted in decimal or hexadecimal. And if you wanted to read all sixteen inputs at once, just request and store two bytes of data instead of one.

For our last example – a demonstration of using port A as outputs and port B as inputs. Four LEDs with matching resistors are connected to port A outputs 0~3, with the buttons connected as per example 41.2. Here is the sketch:

By now there shouldn’t be any surprises in the last example – it receives a byte that represents port B, and sends that byte out to port A to turn on the matching outputs and LEDs. For the curious, here it is in action:

So there you have it… another way to massively increase the quantity of digital I/O pins on any Arduino system by using the I2C bus. You can get the MCP23017 from Tronixlabs.

visit tronixlabs.com

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 forum – dedicated to the projects and related items on this website.

Posted in arduino, education, I2C, lesson, MCP23017, microcontrollers, tutorial

Tutorial: Gravitech Arduino Nano MP3 Player

Hello readers

[Update: 21/05/2013. Tutorial now out of date, and I don’t have a Nano to test it with the new code. Try this instead. If you have hardware questions or enquiries relating to the Arduino Nano or MP3 board, please direct them to Gravitech via their contact page.

Posted in arduino, gravitech, learning electronics, lesson, microcontrollers, mp3, tutorial

Kit Review – Snootlab Rotoshield

Hello Readers

[Update: 11/12/11 – Added example code and video]

In this article we will examine yet another product from a bundle sent for review by Snootlab, a Toulouse, France-based company that in their own words:

… designs and develops electronic products with an Open Hardware and Open Source approach. We are particularly specialized in the design of new shields for Arduino. The products we create are licensed under CC BY-SA v3.0 (as shown in documents associated with each of our creations). In accordance with the principles of the definition of Open Source Hardware (OSHW), we have signed it the 10th February 2011. We wish to contribute to the development of the ecosystem of “do it yourself” through original designs of products, uses and events.

Furthermore, all of their products are RoHS compliant and as part of the Open Hardware commitment, all the design files are available from the Snootlab website.

The subject of the review is the Snootlab Rotoshield – a motor-driver shield for our Arduino systems. Using a pair of L293 half-bridge motor driver ICs, you can control four DC motors with 256 levels of speed, or two stepper motors. However this is more than just a simple motor-driver shield… The PCB has four bi-colour LEDs, used to indicate the direction of each DC motor; there is a MAX7313 IC which offers another eight PWM output lines; and the board can accept external power up to 18V, or (like other Snootlab shields) draw power from a PC ATX power supply line.

However as this is a kit, let’s follow construction, then explore how the Rotoshield could possibly be used. [You can also purchase the shield fully assembled – but what fun would that be?] Assembly was relatively easy, and you can download instructions and the schematic files in English. As always, the kit arrives in a reusable ESD bag:

There are some SMD components, and thankfully they are pre-soldered to the board. These include the SMD LEDs, some random passives and the MAX7313:

Thankfully the silk-screen is well noted with component numbers and so on:

All the required parts are included, including stackable headers and IC sockets:

It is nice to not see any of the old-style ceramic capacitors. The people at Snootlab share my enthusiasm for quality components. The assembly process is pretty simple, just start with the smaller parts such as capacitors:

… then work outwards with the sockets and terminals:

… then continue on with the larger, bulkier components. My favourite flexible hand was used to hold the electrolytics in place:

… followed with the rest, leaving us with one Rotoshield:

If you want to use the 12V power line from the ATX socket, don’t forget to bridge the PCB pads between R7 and the AREF pin. The next thing to do is download and install the snooter library to allow control of the Rotoshield in your sketches. There are many examples included with the library that you can examine, just select File > Examples > snootor in the Arduino IDE to select an example. Function definitions are available in the readme.txt file included in the library download.


After acquiring a tank chassis with two DC motors, it was time to fire up the Rotoshield and get it to work. From a hardware perspective is was quite simple – the two motors were connected to the M1 and M2 terminal blocks, and a 6V battery pack to the external power terminal block on the shield. The Arduino underneath is powered by a separate PP3 9V battery.

In the following sketch I have created four functions – goForward(), goBackward(), rotateLeft() and rotateRight(). The parameter is the amount of time in milliseconds to operate for. The speed of the motore is set using the Mx.setSpeed() function in void Setup(). Although the speed range is from zero to 255, this is PWM so the motors don’t respond that well until around 128. So have just set them to full speed. Here is the demonstration sketch:

… and the resulting video:

For support, visit the Snootlab website and customer forum in French (use Google Translate). However as noted previously the team at Snootlab converse in excellent English and have been easy to contact via email if you have any questions. Snootlab products including the Snootlab Rotoshield are available directly from their website. High-resolution images available on flickr.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, follow on twitterfacebook, or join our Google Group.

[Disclaimer – the products reviewed in this article are promotional considerations made available by Snootlab]

Posted in arduino, I2C, kit review, L293, MAX7313, microcontrollers, motor shield, product review, rotoshield, snootlabComments (5)

Tutorial: Control AC outlets via SMS

Learn how to control AC outlets via SMS text message. This is chapter thirty-three of a series originally titled “Getting Started/Moving Forward 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

Assumed understanding for this article is found in part one. If you have not already done so, please read and understand it.

In this chapter we will continue with the use of the SM5100 cellular shield to turn digital outputs on and off via SMS. However please read chapters twenty-six and twenty-seven first if you are unfamiliar with using the GSM shield with Arduino. As an extension of chapter twenty-seven, we will use our Arduino to turn on or off AC outlets via a common remote-control AC outlet pack. Please note this is more of a commentary of my own experience, and not an exact tutorial. In other words, by reading this I hope you will gain some ideas into doing the necessary modifications yourself and in your own way.

Firstly, we need some remote-control AC outlets. Most electrical stores or giant retail warehouses may have something like this:


Nothing too original, just a wireless remote control that can switch on or off receiver outlets on a choice of four radio frequencies. Before moving forward I would like to acknowledge that this article was inspired by the wonderful book Practical Arduino – Cool Projects for Open Source Hardware by Jon Oxer and Hugh Blemings. In chapter two an appliance remote-control system is devised using a similar system.

At first glance the theory behind this project is quite simple – using the hardware in example 27.2, instead of controlling LEDs, activate the buttons on the wireless remote control for the AC outlets – leaving us with AC outlets controlled via SMS. However there are a few things to keep in mind and as discovered during the process, various pitfalls as well.

Before voiding the warranty on your remote control, it would be wise to test the range of the remote control to ensure it will actually work in your situation. I found this was made a lot easier by connecting a radio to the remote outlet – then you can hear when the outlet is on or off. If this is successful, make a note of the amount of time required to press the on and off buttons – as we need to control the delay in our Arduino sketch.

The next step is to crack open the remote control:


… and see what we have to work with:


Straight away there are two very annoying things – the first being the required power supply – 12 volts; and the second being the type of button contacts on the PCB. As you can see above we only have some minute PCB tracks to solder our wires to. It would be infinitely preferable to have a remote control that uses actual buttons soldered into a PCB, as you can easily desolder and replace them with wires to our Arduino system. However unless you can casually tear open the remote control packaging in the store before purchase, it can be difficult to determine the type of buttons in the remote.

As you can see in the photo above, there is an off and on pad/button each for four channels of receiver. In my example we will only use two of them to save time and space. The next question to solve is how to interface the Arduino digital outputs with the remote control. In Practical Arduino, the authors have used relays, but I don’t have any of those in stock. However I do have a quantity of common 4N25 optocouplers, so will use those instead. An optocoupler can be thought of as an electronic switch that is isolated from what is it controlling – see my article on optocouplers for more information.

Four optocouplers will be required, two for each radio channel. To mount them and the associated circuitry, we will use a blank protoshield and build the Arduino-remote control interface onto the shield. The circuitry for the optocoupler for each switch is very simple, we just need four of the following:

As the LED inside the optocoupler has a forward voltage of 1.2 volts at 10mA, the 390 ohm resistor is required as our Arduino digital out is 5 volts. Dout is connected to the particular digital out pin from the Arduino board. Pins 4 and 5 on the optocoupler are connected to each side of the button contact on our remote control.

The next consideration is the power supply. The remote control theoretically needs 12 volts, however the included battery only measured just over nine. However for the optimum range, the full 12 should be supplied. To save worrying about the battery, our example will provide 12V to the remote control. Furthermore, we also need to supply 5 volts at a higher current rating that can be supplied by our Arduino. In the previous GSM chapters, I have emphasised that the GSM shield can possibly draw up to two amps in current. So once again, please ensure your power supply can deliver the required amount of current. From experience in my location, I know that the GSM shield draws around 400~600 milliamps of current – which makes things smaller and less complex.

The project will be supplied 12 volts via a small TO-92 style 78L12 regulator, and 5 volts via a standard TO-220 style 7805 regulator. You could always use a 7812, the 78L12 was used as the current demand is lower and the casing is smaller. The power for the whole project will come from a 15V DC 1.5A power supply. So our project’s power supply schematic will be as follows:

Now to mount the optocouplers and the power circuitry on the blank protoshield. Like most things in life it helps to make a plan before moving forward. I like to use graph paper, each square representing a hole on the protoshield, to plan the component layout. For example:

It isn’t much, but it can really help. Don’t use mine – create your own, doing so is good practice. After checking the plan over, it is a simple task to get the shield together. Here is my prototype example:


It isn’t neat, but it works. The header pins are used to make connecting the wires a little easier, and the pins on the right hand side are used to import the 15V and export 12V for the remote. While the soldering iron is hot, the wires need to be soldered to the remote control. Due to the unfortunate size of the PCB tracks, there wasn’t much space to work with:


But with time and patience, the wiring was attached:


Again, as this is a prototype the aesthetics of the modification are not that relevant. Be careful when handling the remote, as any force on the wiring can force the soldered wire up and break the PCB track. After soldering each pair of wires to the button pads, use the continuity function of a multimeter to check for shorts and adjust your work if necessary.

At this stage the AC remote control shield prototype is complete. It can be tested with a simple sketch to turn on and off the related digital outputs. For example, the following sketch will turn on and off each outlet in sequence:

Now to get connected with our GSM shield. It is a simple task to insert the remote shield over the GSM shield combination, and to connect the appropriate power supply and (for example) GSM aerial. The control sketch is a slight modification of example 27.2, and is shown below

The variable pressdelay stores the amount of time in milliseconds to ‘press’ a remote control button. To control our outlets, we send a text message using the following syntax:

Where a/b are remote channels one and two, and x is replaced with 0 for off and 1 for on.

So there you have it – controlling almost any AC powered device via text message from a cellular phone. Imagine trying to do that ten, or even five years ago. As always, now it is up to you and your imagination to find something to control or get up to other shenanigans.


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 AC power, arduino, CEL-00675, CEL-09607, cellphone hacking, cellular, GSM, hardware hacking, lesson, SM5100, SMS, tutorial

Tutorial: Arduino and Infra-red control

Learn how to use Arduino and infra-red remote controls in chapter thirty-two of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Updated 10/07/2013

In this article we will look at something different to the usual, and hopefully very interesting and useful – interfacing our Arduino systems with infra-red receivers. Why would we want to do this? To have another method to control our Ardiuno-based systems, using simple infra-red remote controls.

A goal of this article is to make things as easy as possible, so we will not look into the base detail of how things work – instead we will examine how to get things done. If you would like a full explanation of infra-red, perhaps see the page on Wikipedia. The remote controls you use for televisions and so on transmit infra-red beam which is turned on and off at a very high speed – usually 38 kHz, to create bits of serial data which are then interpreted by the receiving unit. As the wavelength of infra-red light is too high for human eyes, we cannot see it. However using a digital camera – we can. Here is a demonstration video of IR codes being sent via a particularly fun kit – the adafruit TV-B-Gone:

Now to get started. You will need a remote control, and a matching IR receiver device. The hardware and library used in this tutorial only  supports NEC, Sony SIRC, Philips RC5, Philips RC6, and raw IR protocols. Or you can purchase a matching set for a good price, such as this example:


Or you may already have a spare remote laying around somewhere. I kept this example from my old Sony Trinitron CRT TV after it passed away:


It will more than suffice for a test remote. Now for a receiver – if you have purchased the remote/receiver set, you have a nice unit that is ready to be wired into your Arduino, and also a great remote that is compact and easy to carry about. To connect your receiver module – as per the PCB labels, connect Vcc to Arduino 5V, GND to Arduino GND, and D (the data line) to Arduino digital pin 11.

Our examples use pin 11, however you can alter that later on. If you are using your own remote control, you will just need a receiver module. These are very cheap, and an ideal unit is the Vishay TSOP4138 (data sheet .pdf). These are available from element-14 and the other usual retail suspects. They are also dead-simple to use. Looking at the following example:

From left to right the pins are data, GND and Vcc (to Arduino +5V). So it can be easily wired into a small breadboard for testing purposes. Once you have your remote and receiver module connected, you need to take care of the software side of things. There is a new library to download and install, download it from here. Please note that library doesn’t work for Arduino Leonardo, Freetronics Leostick, etc with ATmega32U4. Instead, use this library (and skip the modification steps below). Extract the IRremote folder and place into the ..\arduinoxxx\libraries folder. Then restart your Arduino IDE if it was already open.

Using Arduino IDE v1.0 or greater? Open the file “IRRemoteInt.h” in the library folder, and change the line

Then save and close the file, restart the Arduino IDE and you’re set.

With our first example, we will receive the commands from our remote control and display them on the serial monitor:

Open the serial monitor box, point your remote control to the receiver and start pressing away. You should see something like this:

What have we here? Lots of hexadecimal numbers. Did you notice that each button on your remote control resulted in an individual hexadecimal number? I hope so. The number FFFFFFFF means that the button was held down. The remote used was from a yum-cha discount TV. Now I will try again with the Sony remote:

This time, each button press resulted in the same code three times. This is peculiar to Sony IR systems. However nothing to worry about. Looking back at the sketch for example 32.1, the

section is critical – if a code has been received, the code within the if statement is executed. The hexadecimal code is stored in the variable

with which we can treat as any normal hexadecimal number. At this point, press a few buttons on your remote control, and take a note of the matching hexadecimal codes that relate to each button. We will need these codes for the next example…

Now we know how to convert the infra-red magic into numbers, we can create sketches to have our Arduino act on particular commands. As the IR library returns hexadecimal numbers, we can use simple decision functions to take action. In the following example, we use switch…case to examine each inbound code, then execute a function. In this case we have an LCD module connected via I2C, and the sketch is programmed to understand fifteen Sony IR codes. If you don’t have an LCD you could always send the output to the serial monitor. If you are using the DFRobot I2C LCD display, you need to use Arduino v23.

Furthermore you can substitute your own values if not using Sony remote controls. Finally, this sketch has a short loop after the translateIR(); function call which ignores the following two codes – we do this as Sony remotes send the same code three times. Again. you can remove this if necessary. Note that when using hexadecimal numbers in our sketch we preced them with 0x:

And here it is in action:

You might be thinking “why would I want to make things appear on the LCD like that?”. The purpose of the example is to show how to react to various IR commands. You can replace the LCD display functions with other functions of your choosing.

At the start working with infra-red may have seemed to be complex, but with the previous two examples it should be quite simple by now. So there you have it, another useful way to control our Arduino systems. Hopefully you have some ideas on how to make use of this technology. In future articles we will examine creating and sending IR codes from our Arduino. Furthermore, a big thanks to Ken Shirriff for his Arduino library.


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, control, DFR0107, dfrobot, education, infrared, IR, learning electronics, lesson, microcontrollers, remote, tronixstuff, tutorialComments (17)

Tutorial: Arduino and GSM Cellular – Part Two

Continue to learn about connecting your Arduino to the cellular network with the SM5100 GSM module shield. This is chapter twenty-seven of a series originally titled “Getting Started/Moving Forward 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

Assumed understanding for this article is found in part one. If you have not already done so, please read and understand it. In this instalment we continue with bare projects which you can use as a framework for your own creations.

Reach out and control something

First we will discuss how to make something happen by a simple telephone call. And the best thing is that we don’t need the the GSM module to answer the telephone call (thereby saving money) – just let the module ring a few times. How is this possible? Very easily. Recall example 26.1 – we monitored the activity of the GSM module by using our terminal software. In this case what we need to do is have our Arduino examine the text coming in from the serial output of the GSM module, and look for a particular string of characters.

When we telephone the GSM module from another number, the module returns the text as shown in the image below:


We want to look for the text “RING”, as (obviously) this means that the GSM shield has recognised the ring signal from the exchange. Therefore need our Arduino to count the number of rings for the particular telephone call being made to the module. (Memories – Many years ago we would use public telephones to send messages to each other. For example, after arriving at a foreign destination we would call home and let the phone ring five times then hang up – which meant we had arrived safely). Finally, once the GSM shield has received a set number of rings, we want the Arduino to do something.

From a software perspective, we need to examine each character as it is returned from the GSM shield. Once an “R” is received, we examine the next character. If it is an “I”, we examine the next character. If it is an “N”, we examine the next character. If it is a “G”, we know an inbound call is being attempted, and one ring has occurred. We can set the number of rings to wait until out desired function is called. In the following example, when the shield is called, it will call the function doSomething() after three rings.

The function doSomething() controls two LEDs, one red, one green. Every time the GSM module is called for 3 rings, the Arduino alternately turns on or off the LEDs. Using this sketch as an example, you now have the ability to turn basically anything on or off, or call your own particular function. Another example would be to return some type of data, for example you could dial in and have the Arduino send you a text message containing temperature data.

And now for a quick video demonstration. The first call is made, and the LEDs go from red (off) to green (on). A second call is made, and the LEDs go from green (on) to red (off). Although this may seem like an over-simplified example, with your existing Ardiuno knowledge you now have the ability to run any function by calling your GSM shield.

Control Digital I/O via SMS

Now although turning one thing on or off is convenient, how can we send more control information to our GSM module? For example, control four or more digital outputs at once? These sorts of commands can be achieved by the reception and analysis of text messages.

Doing so is similar to the method we used in example 27.1. Once again, we will analyse the characters being sent from the GSM module via its serial out. However, there are two AT commands we need to send to the GSM module before we can receive SMSs, and one afterwards. The first one you already know:

Which sets the SMS mode to text. The second command is:

This command tells the GSM module to immediately send any new SMS data to the serial out. An example of this is shown in the terminal capture below:


Two text messages have been received since the module was turned on. You can see how the data is laid out. The blacked out number is the sender of the SMS. The number +61418706700 is the number for my carrier’s SMSC (short message service centre). Then we have the date and time. The next line is the contents of the text message – what we need to examine in our sketch.

The second text message in the example above is how we will structure our control SMS. Our sketch will wait for a # to come from the serial line, then consider the values after a, b, c and d – 0 for off, 1 for on. Finally, we need to send one more command to the GSM module after we have interpreted our SMS:

This deletes all the text messages from the SIM card. As there is a finite amount of storage space on the SIM, it is prudent to delete the incoming message after we have followed the instructions within. But now for our example. We will control four digital outputs, D9~12. For the sake of the exercise we are controlling an LED on each digital output, however you could do anything you like. Although the sketch may seem long and complex, it is not – just follow it through and you will see what is happening:

And now for a video demonstration:

So there you have it – controlling your Arduino digital outputs via a normal telephone or SMS. Now it is up to you and your imagination to find something to control, sensor data to return, or get up to other shenanigans.

If you enjoyed this article, you may find this of interest – controlling AC power outlets via SMS.


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, CEL-00675, CEL-09607, cellphone hacking, cellular, GSM, hardware hacking, lesson, microcontrollers, SM5100, SMS, tutorial

Tutorial – Arduino Uno and SM5100B GSM Cellular

Shield is now obsolete. Contact your hardware supplier for support.

Posted in arduino, CEL-00675, CEL-09607, cellphone hacking, cellular, GSM, lesson, SMS, tronixstuff, tutorial

Kit Review – adafruit industries TV-B-Gone

[Updated 17/01/2013]

In this review we examine an easy to build kit from adafruit industries that offers literally hours and hours of fun, if you like to get up to some mischief – the TV-B-Gone. This fascinating little device is basically an infra-red remote control for televisions and some monitors. It has a microcontroller programmed with the “off” code for a wide range of display brands, and four very strong infra-red transmitting LEDs, two with a wide beam, and two with a narrow but longer beam.

Here is the little culprit in standard assembled form:


It is a very easy kit to assemble, once again the team at adafruit have published an extensive amount of information, from assembly tutorials to how it works, and even the design itself as the kit is open-source hardware. So in this article you can follow the assembly, and use of this bag of fun.

As usual, this kit arrives in a resealable, anti-static bag. After ensuring I had the correct parts, from the documentation on the adafruit website, it was time to follow the simple instructions and start getting it together. Now this will be the second time I have built a TV-B-Gone… the first one is in the photo above, and had me removed from a department store (thanks Myer…) – so this time I am rebuilding it to fit inside a typical baseball cap.

Soldering it was quite simple, the PCB is solder-masked and has a very well detailed silk-screen:


Just following the instructions, and being careful not to rush is the key. Another feature of adafruit kits is that the are designed very well with regards to troubleshooting. For example, you have the opportunity to test it before finishing. So at this stage you can fit the AA cells and power it up, if the LED blinks you’re all good:


And we’re done… almost.


For installation into the hat, the button and the LEDs will need to be a distance away from the PCB. At this stage I was not sure where to put the button, so for now it can stay on the side of the cap:


Naturally you can use any momentary push button, however I will use the included example (above) with a length of wire. With this style of hat, especially a black one, slight bulges underneath the surface do not seem that apparent, however it is wiser to spread out the entire unit:


Although thinner AAA cells could be used for the power supply, for a good day’s action you will want the extra capacity of AA cells, so we’ll stick with them for now. The next step was to wire up the LEDs. They were connected individually to the PCB with lengths of wire, and heatshrink was used to insulate and darken the legs:





And finally the finished product, ready for insertion into a piece of clothing, or in our case – a cap:


At this point it was time to take it for a test toast. The quickest way to test an infra-red transmitter is to look at the LEDs through a digital camera – it can display the infra-red wavelengths whereas the human eye cannot see them. For example:

Those LEDs can get very bright (in infra-red terms), and is also how night-illumination for digital security cameras work. If you had a lot of those LEDs pointing at a security camera at night, you could blind it. That gives me an idea…


Assembling the kit in this format gives you lots of options for hiding it. For example, you could:

  • put the PCB and power in a jacket’s inside pocket, and have the LEDs poke out the neck;
  • place them in a cap as we are;
  • use a large ladies’ handbag, with the LEDs out the top, and the button underneath a handle;
  • sew the LEDs into the head-cover of a hooded jacket (with some longer leads) and have the PCB, power and button in the pockets

So here are the LEDs mounted under the brim of the cap:


If you are going to staple them in, be careful not to puncture the wires. The ends of the staple should come through to the top of the brim – in this case I covered them with black ink from a felt pen so they would blend in. The button lead’s position is down to personal preference, in my case the button is just poking out next to the strap on the back of the cap. So all I need to do is appear to scratch the back of my head to activate the TV-B-Gone.

And here is the finished product, with an unfinished author:

Well by now you want to see it working. So here you are… I went on a field trip wandering about the central business district of Brisbane, Australia:

My apologies for the shaky footage, doing this isn’t something you can really capture with a camera and a tripod. 🙂 The problem was getting close enough, or most places had either covered their IR receiver, had a brand of TV not recognised by the TV-B-Gone, or used a large monitor instead of a television. But it was fun nevertheless.

In conclusion, this is an easy to assemble kit which is fun and certainly will get you into harmless trouble. Again, this is the type of kit that would be good for those who are being introduced to the fascinating world of electronics (etc) as it is quick to build, and does something with the “real world”  that young people love so much. Or anyone else for that matter.

As much fun as it is to switch off televisions and advertising monitors, I would hope that end users will still be responsible with their TV-B-Gone use. Please head into a department store, your favourite eatery, coffee shop or mall and switch off the TVs.  However, please do not turn off displays in railway stations, airports or other places where the authorities will take offence. You will get in real trouble. Or if you’re feeling suicidal, go switch off the TVs at the OTB.

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.
[Note – this kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Posted in adafruit, kit review, learning electronics, tv-b-goneComments (13)

Getting Started with Arduino – Chapter Thirteen

This is part of a series 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.

Welcome back fellow arduidans!

This chapter we will examine piezo buzzers, continue with our alarm clock, and then spend more time with the wireless radio modules by creating some remote control systems and sending various data over the airwaves. So let’s go!

Sometimes you would like to make some noise. For warnings, fun, or to annoy people. A very simple and inexpensive way to do this is with a piezoelectric buzzer. In simple terms, it contains a disc of metal that can deform when a current is applied to it. If you apply an alternating current at a high enough frequency, the disc will move fast enough to create a sound wave, something we can hear.

This is an example of a small piezo buzzer:


This example was very cheap, less than $2.  Here is the data sheet: PS1240.pdf. It can run from between 3 and 30 volts AC – which thankfully the output from our Arduino falls between. But how do you output AC from an Arduino? There are several ways, however the easiest is using pulse-width modulation (PWM). If you look at your Arduino’s digital output sockets, some are labelled PWM. Using the function analogWrite(); you can send a PWM signal to the buzzer. For example:

The sketch above will beep the piezo on and off, and be somewhat annoying. Perfect. However with the analogWrite(); function it is impossible to use the full frequency range of the piezo buzzer. With a value of 254 for the duty cycle, the frequency generated is around 1500 Hz:


Later on we will explore ways to create a better range of sounds. But now to use that buzzer in our alarm clock to help wake people up.

Continuing on from exercise 12.1, this chapter we will add some more features to the clock. First of all is the piezo buzzer. As we just discussed above, using it is quite simple. On the hardware side of things, we can replace the resistor and LED connected between digital pin 6 and ground with our piezo buzzer. On the software side of things, instead of digitalWrite(6, HIGH); we use analogWrite(6,128);. Very easy. And here is a short video – with sound!

Moving on, it’s time to clean up the alarm function in general. Most alarm clocks have a snooze function, so let’s add one as well. When the alarm sounds, the user presses button four to turn off the buzzer, and is then asked if they want to snooze. Button one is yes and four is no. If yes, add ten minutes to the alarm time and carry on as normal. When adding the ten minutes be sure to check for increasing the hour as well, and also take into account the jump from 2359h to 0000h (or 2400h). If the user presses no, the alarm is switched off and the user warned with the flashing “OFF”.

Example 13.1Here is a demonstration of what I came up with:

The hardware is the same as exercise 12.1, except the LED and resistor from digital pin 6 to GND has been replaced by the piezo buzzer as described earlier. You will find the snooze function is controlled in the checkalarm(); function in the sketch.


In chapter eleven we started to examine the inexpensive serial data transmitter/receiver pairs. In this chapter we will continue working with them, to create the backbone of various remote control and data transmission ideas for you to use. For our next example, consider a simple remote control with four channels. That is, it has four buttons, and the transmitter will send out the state of the four buttons, high or low.

This would be useful for a remote control toy or a perhaps robot. The sketches are quite simple. The transmitter reads the buttons with digitalRead(); then transmits a single letter a~h – which is code for a button and its state. For example, a means button 1 is low, h means button 4 is high. The receiver just decodes that a~h code and sends the result to the serial monitor window. Here is the sketch for the transmitter and receiver.

To save time I will use the button board created in example 12.3. Here are the schematics for the transmitter and receiver sections:


And set up:


And finally a video of the serial monitor showing the button states:

Now that we have the data being sent across, let’s get some switching happening. Using the same transmitter system as example 13.2, we will turn on or off four LEDs at the receiving end. Of course you could use relays, transistors, 74HC4066s, etc instead. Our sketch decodes the transmitted data once more, but sets the digital pins high or low depending on the received code. Here is the schematic for the new receiver:


… and the board laid out:


And again a quick demonstration video:

Now that you can turn the LEDs on or off with a push of a button, there are a few other ways of controlling those digital outputs with the remote control rig without altering the hardware.

For out next example, we will control two digital outputs with the four buttons, as each output will have an on and off button. Consider this sketch; and the following demonstration video:

So there you have various ways to control digital outputs and send basic data across a wireless radio serial data link.


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Posted in 315 MHz, 433 MHz, arduino, education, learning electronics, lesson, microcontrollers, piezo, tutorial, wirelessComments (12)

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