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Control relays over the Internet with Arduino Turning items on and off remotely via the internet has generally been a complex and expensive task due to the hardware and knowledge required. Not any more. Here we show how easy and inexpensive it can be to control four or more relays over the Internet using open-source Arduino-based hardware. By JOHN BOXALL Fig.2: the Freetronics RELAY4 relay driver module. It interfaces directly to the EtherTen module & uses FETs to switch external relays. Fig.1 (left): the Freetronics EtherTen module is Arduino Uno-compatible and has an onboard Ethernet interface. I T’S NOT DIFFICULT to remotely control relays via the internet. In this article, we’ll first look at the hardware required, then explain the software and network requirements. After that, we’ll look at how commands are sent over the internet using a web browser to control the relays. If you are unfamiliar with the Arduino environment, please refer to the article by Jonathan Oxer titled “Arduino – What’s All The Fuss About?” in the January 2012 issue of SILICON CHIP or visit the homepage at http://www. arduino.cc Arduino board and uses FETs to switch the relay coils. It also includes reverse-connected power diodes to suppress back-EMF pulses when the relays are turned off. Connecting the relay module to the Arduino board is very simple: The hardware Note that when using an Ethernet-enabled Arduino board, digital pins 10-13 are used by the Ethernet interface and can’t be used for other purposes. And in the case of the EtherTen board, digital pin 4 is used for the microSD card. Note that, for this project, we don’t use digital pin 8 either and we’ll explain the reason for this shortly. The next consideration is the power supply for the relay coils. Although there is a 5V power supply available from the Arduino board, it’s unable to supply enough current to The heart of the system is an Arduino Uno-style board with an Ethernet shield. In this case, we have used the Freetronics EtherTen board which conveniently combines both into a single unit, thereby saving space and money – see Fig.1. The EtherTen board can control up to four relays via a Freetronics RELAY4 4-channel relay control module – see Fig.2. This module interfaces directly to the EtherTen 70  Silicon Chip • • • • • Input 1 to Arduino D2 Input 2 to Arduino D3 Input 3 to Arduino D5 Input 4 to Arduino D6 Logic GND to Arduino GND siliconchip.com.au drive most conventional relay coils. What’s more, it cannot be used to power relays with 12V (or higher) coils. In either case, you will have to connect an external DC power supply with the required ratings to the RELAY4 board’s power terminals (bottom-left of Fig.3). On the other hand, if you can keep the current draw under 150mA and are using solid-state 5V relays (such as Jaycar SY4092) with very low switching currents, the on-board Arduino 5V supply will be enough. With a 5V supply, the RELAY4 board itself draws around 13mA with all LEDs on. Add four relays drawing just 20mA each and you can comfortably power the lot from the Arduino. In that case, connect the positive pin from the RELAY4 power terminal to the Arduino +5V pin. Testing You can then test the connections to the RELAY4 board with a simple Arduino sketch (software program) that turns the outputs on and off – as indicated by the on-board RELAY4 LEDs. Once your hardware has been connected, enter and upload the following sketch using the Arduino IDE (Integrated Development Environment): void setup() { DDRD = B11111111; // set PORTD (digital 7~0) to outputs } void loop() { PORTD = B01101100; // set D2, D3, D5, D6 HIGH delay(250); PORTD = B00000000; // set D2, D3, D5, D6 LOW delay(250); } At this stage, all four LEDs should be blinking on and off at 2Hz. If not, check the wiring between the two boards, including the GND line. Software & network requirements To control our Arduino over the Internet, we use a free online service called “Teleduino”. It allows us to send commands to an Arduino board (via the Internet) using simple commands in the form of URLs similar to that used to refer to a web page. You can find out more at the Teleduino website at www. teleduino.org To identify an individual Arduino board to the Tele­ duino service, we use a unique key in the form of a long hexadecimal number. This key is issued by the Teleduino service and is inserted into the Arduino sketch and also into the commands issued to control the board. To generate a key, simply go to https://www.teleduino. org/tools/request-key and complete the required fields. A short time later, your key will arrive via email – remember to store this for later retrieval. It will be a long string of characters, eg, 18F5F4749B058F952ABCDEF8534B2BBF. The next step is to download and install the Teleduino Arduino library into the IDE. The latest library can be found at https://www.teleduino.org/downloads/ Extract the library folder and copy it to the arduino-1.0.1/libraries folder in your IDE installation. If your IDE is running, you will need to restart it in order to use the library. siliconchip.com.au Fig.3: here’s how to connect the external hardware & wire the power supply to the relay driver module. You now have to prepare the Teleduino sketch for the Arduino board. This sketch connects the Arduino to the Teleduino server and also executes received commands via the service. The sketch is included with the library, so in the IDE select File –> Examples –> Teleduino328 –> TeleduinoEthernetClientProxy. Before uploading the sketch, the unique Teleduino key needs to be inserted so the Arduino can identify itself to the service. To do this, go to https://www.teleduino.org/ tools/arduino-sketch-key, enter your Teleduino key into the field and click “Generate Code”. This will appear as an array in Arduino format as shown, for example, in Fig.4. That done, scan through the Arduino sketch currently loaded in the IDE, locate the same byte variable (it should start on line 36) and replace the array full of zeros with your Teleduino key array – see Fig.5 (for example). Once you have modified the sketch as above, upload it to your Arduino as normal. You should also save the sketch so you don’t need to repeat the key-insertion process in the future. Note that if you are going to control multiple Arduino boards, you will need multiple Teleduino keys. Just remember to keep track of the key uploaded to each board. The next step is to test that the Arduino is connecting to the Teleduino service by monitoring the connection status. This can be done using a LED indicator connected via a 560Ω resistor between the Arduino’s D8 pin and GND, as shown in Fig.6. Once the indicator LED is in place, connect the Arduino to your router via a network cable, apply power and watch the LED. After a few moments, the LED will start blinking to indicate the status of the connection to the Teleduino service. Fig.4: a Teleduino key array in Arduino sketch format. Fig.5: the Teleduino key array after insertion into the Arduino sketch. March 2013  71 (3.3V) (5V) POWER Fig.6: the status LED is connected between D8 and GND of the Arduino module as shown here. (Vin) SCK (RST) (AREF) MISO MOSI SS (D9) (A1) (A2) (A3) (A4) ANALOG INPUTS (A0) (A5) (D8) (D7) DIGITAL INPUTS/OUTPUTS ARDUINO ETHERNET SHIELD PWM (D6) PWM (D5) PWM R1 560 SS (D3) PWM A  LED1 (D2) (D1) Tx (D0) Rx K (GND) At the time of writing, the following blink parameters are used: • • • • • • • 1 blink: 2 blinks: 3 blinks: 4 blinks: 5 blinks: 6 blinks: 10 blinks: initialising starting network connection connecting to the Teleduino server authentication successful session already exists for supplied key invalid or unauthorised key connection dropped It is normal for the LED to work its way up from one to four blinks. After the connection and authentication is successful, the LED will then blink very briefly every 10 seconds or so. This signifies that all is well. If your LED shows five blinks, just reset the Arduino board. If your LED shows six blinks, check your Teleduino key in the control sketch and re-upload it to the Arduino. And finally, if it blinks 10 times, the Internet connection has dropped out. Although the above procedure may seem somewhat tedious, it is necessary to establish that everything is working correctly. Once you’ve done that, the status LED can be removed if desired but we suggest keeping it to aid troubleshooting if you strike problems in the future. Default relay settings The final step in setting up the Teleduino service is to decide what the default settings will be for each of the relays. These are the settings that the relays revert to when the Arduino board is turned on or reset, loses the Internet connection or the network cable is removed. You can set the defaults after your Arduino has connected to Teleduino by browsing to https://www.teleduino. org/tools/manage-presets After entering your Teleduino key, a large selection of options will be displayed. Scroll down to the “Pins” section (see Fig.7) and change the 72  Silicon Chip Fig.7: this section of the Teleduino presets page allows you to set the defaults for the Arduino’s digital I/O pins. mode of the Arduino pins you’re using to OUTPUT. Then, depending on your needs, you can set the default relay status with the value parameter. Controlling the RELAY4 module To control the RELAY4 module, first launch your web browser (on a computer, smartphone or tablet). You can then control the Arduino’s digital pins and thus the relays by going to http://us01.proxy.teleduino.org/api/1.0/328.php ?k=999999&r=setDigitalOutput&pin=X&output=Y There are three parameters you need to enter into this page. The first is your Teleduino key – simply replace 999999 with your key. The next is the Arduino digital pin to control – replace “X” with the pin number. And finally, to turn the pin on or off, replace Y with a “0” for off or a “1” for on. For example, to turn on relay 1, you would use http://us01. proxy.teleduino.org/api/1.0/328.php?k=999999&r=set DigitalOutput&pin=2&output=1 To turn it off again, simply change the final “1” to “0”. You may find it convenient to bookmark the various URLs to make sending commands much easier. Furthermore, the use of URL-shortening services such as http:// bit.ly can reduce their length to more manageable sizes. By checking the status LEDs on the RELAY4 board, you can test the pin control without needing to wire up your entire project at the start. Also, when you send a command, the Teleduino server will return a message if the action has been successful or not. If the command worked, an output similar to the following will appear in the web page: {"status":200,"message":"OK","response":{"result":1,"time": 0.2338559627533,"values":[]}} Conversely, if it was not successful, you will see: {"status":403,"message":"Key is offline or invalid.","response":[]} This tells you that the Arduino has lost connection to the Teleduino servers. Conclusion Once you have run through the set-up procedure, controlling the relays remotely is quite simple. If you need to control more relays, either add another RELAY4 board or check out the Freetronics RELAY8 board. Finally, the Teleduino service allows web-based control of much more than your Arduino’s digital outputs – refer SC to http://www.teleduino.org for more information. siliconchip.com.au