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iot:labs:06 [2017/09/11 09:34]
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-====== Lab 6: Light Blink ======+====== Lab 6: Connect and use an LCD ======
 +In this project you are going to connect an LCD to your board and write a short message on it.
 ===== What you need ===== ===== What you need =====
-  ​* One Raspberry Pi connected to Wyliodrin STUDIO; + 
-  * One LED+  ​ One Raspberry Pi connected to Wyliodrin STUDIO; 
-  * One 220 Ohm resistor;+  *  One 16x2 LCD
 +  *  One breadboard;
   * Jumper wires;   * Jumper wires;
-  * Breadboard; 
- {{ :​iot2015:​labs:​leed.png?​80 |}} 
-{{ :​iot2015:​labs:​resist.png?​100 |}} 
 ===== The Setup ===== ===== The Setup =====
-Connect the LED to the Raspberry Pi following the schematics in the figure. +{{ :iot:labs:lcd-expander.jpg?500 |}} 
- +The LCD in the kit is connected to a port expander (MCP23008). This allows ​the LCD to be controlled via the I2C protocolthus reducing ​the number ​of pins you need to connect ​the LCD to. In this caseyou just need to connect the expander ​to GND5V, SCL and SDA pins, according ​to the indicators on the expanderYou can find the appropriate pins in the **Pin Layout** tab. You just need to connect ​the SDA port on the port expander with the SDA pin on the board and so on.
-First of all, you need to distinguish the anode from the cathode. The LED has two legs: one is longer, that one is usually the anode and the shorter one is the cathode. Another way of identifying them is by looking inside the LED. There are two metal parts in it. The smaller one is connected to the anode and the bigger one is connected to the cathode.  +
-{{ :iot:labs:led-blink-schematics.png?300 |}} +
-To understand ​the anode and the cathode of the LED, imagine these two following situations:  +
-  -  The cathode ​is connected ​,through the resistor of course, ​to the ground. This means that the anode will be wired to the GPIO pinwhich has to be //High// in order to make the LED light up. +
-  - The anode is connected to the VCC pin of the board. Which means that, should ​you want to light up the LED, the cathode has to be connected to the GPIO setted to //Low //Don't forget ​this kind of a circuit also requires a resistor.  +
- +
-To sum it upalthough the position of the resistor is not fixed, it can can either ​connect the ground ​to the cathode or the anode to the GPIO pinthe cathode should be connected ​to the ground to obtain ​the usually desired behaviourMeaning you want the LED to light when the GPIO is set to HIGH and not to light when the GPIO is set to LOW. If you put the legs the other way around, ​the effect will be the opposite +
 ===== The Code ===== ===== The Code =====
-Let's see the same application in three different programming languages.  +{{ :iot:labs:lcd-simple-example.png?600 |}} 
- +You go to the Wyliodrin Applications page and create ​a new applicationYou name it and select Streams as programming languageOnce createdyou click on the new application'​s name to open it.
-==== Visual Programming ==== +
-First, you can try it out in Visual Programming.  +
-Here's an example:  +
-{{ :iot2015:labs:blink-application.png?300 |}} +
-The first two blocks will simply print on the screen the messages written inside them.  +
-The // repeat while true// blocks will create ​an endless loopInside ​it, there will be the blocks that turn on and off the LED on the chosen pinThere is also a // delay// blockwhich will insert here a pause of 0.5 seconds between the // on //  state of the LED and the // off // one. +
- +
-==== Python ==== +
- +
-An important feature of Visual Programming in Wyliodrin is that you can easily get the Python code for your projects, just by clicking the // Show code// button. ​  +
-<code python>​ +
-from wyliodrin import * +
-from time import *+
-pinMode (01)+First of allyou need to initialise the LCD. For this, you drag the **run** node and select **Fire once at start** so you make sure that once you run the application a first message is sent. This is only required to trigger the **init LCD** node, so you can assure there is no other message being sent again. For this, drag the **trigger** node and double click on it.
-print('​Led on pin 0 should blink'​) +{{ :iot:​labs:​trigger-block.png?400 |}}
-print('​Press the Stop button to stop'​) +
-while True: +
-  digitalWrite (0, 1) +
-  sleep ((500)/​1000.0) +
-  digitalWrite (0, 0) +
-  sleep ((500)/1000.0) +
-First of all, you need to import ​the //​wyliodrin// ​and //time// modules that will allow you to use some simple functions.+You need to set this node to **wait until reset**. This will make the node to send the first message ​and then wait until it receives a message containing the property **reset**, which will never happen.  
 +Next, the **init LCD** node initializes the LCD.
-Firstly, you have to declare ​the pins you are going to use and their purposeIn this case, pin 0 is used as //OUTPUT//. This is what //​pinMode(0,​1)//​ does (1=OUTPUT, 0=INPUT)+First of all, you need to require ​the **wyliodrin** module, which exposes some simple functions in order to control the LCDOtherwise you would need to implement the protocol in order to control it
-Nextthere are the //print// functions that simply write the text in the shell.+Once you have the **wyliodrin** variablecall the **LiquidCrystal** constructor ​in order to obtain a **LiquidCrystal** object. The constructer receives 0 as parameter.
-Another useful function ​is //​digitalWrite//​. The function receives as parameter the pin and the valueAs you are doing a digital write, the value can be either ​or 1If the value is 0, the pin will have no current. If the value is 1, there is current.+Why is the value 0 the parameter ​of the contructor? This type of LCD communicates with the Raspberry Pi board via that I2C protocolTaking into account how the I2C protocol behavesyou would need to mention ​the bus specific to the LCD, that usually is 32. However, in order to be able to connect multiple LCDs at once, they have three jumpers which can be connected in order to represent values from to 7, thus being able to identify eight different LCDsThis is the value you need to pass to the constructor,​ in this case, no jumper is connected so we passed ​the value 0.
-The //sleep// function makes the program wait for the desired number of seconds.+{{ :​iot:​labs:​init-lcd.png?400 |}}
-All this code is enclosed within ​the //while True// loop that makes it to be run foreveruntil the application is stopped.+What is new at the code presented above is the **context.global.lcd** structure. You need to use this because you want the **lcd** variable ​to be available from other nodes also (Display on LCD node) and **context.global** is a variable accessible to all the nodesso you just set the lcd property and you will be able to use it from any other node.
-==== Useful Functions ==== +{{ :iot:​labs:​display-lcd-simple.png?400 |}}
-You can use the following functions both in Python and JavaScript: +
-  * **wyliodrin.pinMode (pin, mode)** ​configures the specified pin to behave either as an input or an output; +
-  * **wyliodrin.digitalWrite (pin, value)** - writes a HIGH or a LOW value to a digital pin; +
-  * **wyliodrin.delay()** ​pauses the program for the amount of time (in miliseconds) specified as parameter.+
-In order to use these function, import the **wyliodrin** module: +The **display LCD** node is another function node which first clears ​the LCD, then prints a string on itNotice ​that the global **lcd** variable ​is used.
-  * **Python:** from wyliodrin import wyliodrin +
-  * **JavaScript:​** var wyliodrin = require ('​wyliodrin'​);​ +
-===== Tips & Tricks ===== +
-Usually the longer leg is the anode and the shorted one is the cathodeHowever, this is not standard, to make sure which is which, you should know that the cathode leg is always connected to the bigger part inside the LED.+
 ===== Exercises===== ===== Exercises=====
-  - Use one LED to write SOS using the international morse code using Python or JavaScript.{{ :​iot2015:​labs:​international_morse_code.png?​300 |}} +  - Use a temperature sensor ​and display ​the temperature on the LCD.
-  - Create ​traffic lights system that has lights for cars and for pedestrians.  +
-  - Use [[http://​openweathermap.org/​api|Open Weather Map]] to get the temperature ​in Bucharest and light up one of the green, yellow or red LEDs depending ​on the temperature. **Note:​**Use the **requests** module.+
iot/labs/06.txt · Last modified: 2017/09/11 09:39 by alexandru.radovici
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