Building Connected Things with an ESP8266 and Microsoft Azure

Hello, Lua IoT!

In this lab, you will create a simple 'Thing' using Lua on the ESP8266.

Table of Contents
Bill of Materials
Create the Lua Program in ESPlorer
Run the App on the Device
Wire the Huzzah Feather to the Power and Ground Rails
Add a Three Color LED from the kit
Modify the code
Run the Modified App on the Device
Conclusion & Next Steps

In this lab, you will create a simple Thing using a ESP8266 and the Lua programming language.

Bill of Materials

In this lab series you will need the following:

Microsoft Azure IoT Starter Kit w/ Adafruit Feather HUZZAH, including
- RGB LED
- 3 - 560 Ohm Resistors

If you haven’t already done so, follow the setup instructions at ‘Getting Started’.

The Huzzah Feather connects to the physical world through the a set of pins. These pins have various functions, but most are General Purpose Input/Output (GPIO) pins. Because there are so few connections to the Huzzah, some of the pins are used for more than one function and need to be configured before you can use them. In fact, GPIO pins can be used for both input and output and therefore need configuration to tell them how to operate. The inputs can be from switches, sensors or other devices. The outputs can be LEDs, servos, motors or countless other devices. Besides the GPIO Pins there are a set of other pins including:

#0, #2, #4, #5, #12, #13, #14, #15, #16 - GPIO

GND - this is the common ground for all power and logic

BAT - this is the positive voltage to/from the JST jack for the optional Lipoly battery

USB - this is the positive voltage to/from the micro USB jack if connected

EN - this is the 3.3V regulator’s enable pin. It’s pulled up, so connect to ground to disable the 3.3V regulator

3V - this is the output from the 3.3V regulator, it can supply 500mA peak (try to keep your current draw under 250mA so you have plenty for the ESP8266’s power)

RST - this is the reset pin for the ESP8266, pulled high by default. When pulled down to ground momentarily it will reset the ESP8266 system. This pin is 3.3V logic only

EN (CH_PD) - This is the enable pin for the ESP8266, pulled high by default. When pulled down to ground momentarily it will reset the ESP8266 system. This pin is 3.3V logic only

Huzzah Layout

I2C SDA = GPIO #4 (default)

I2C SCL = GPIO #5 (default)

SPI SCK = GPIO #14 (default)

SPI MOSI = GPIO #13 (default)

SPI MISO = GPIO #12 (default)

ADC - Analog to Digital Converter Pin, 1.0V max.

Serial Communication Occurs over TX/RX:

TX - output from the module and is 3.3V logic.

RX - input into the module and is 5V compliant (there is a level shifter on this pin)

Create the Lua Program in ESPlorer

The Lua programming language is a simple language designed to avoid the clutter of many languages. It’s powerful enough and simple enough to make it an effective language for working on devices. It’s also much more user friendly than other languages typically used in small devices, like forth, and more flexible than C.

To write your first lua program for the ESP8266 you’ll only have to write a few lines of code.

Launch ESPlorer.jar, select your serial port, and press the ‘Open’ button

Launch Esplorer, connect your device

Create a new script in Esplorer with these contents. Save it as Lab01.lua

--
-- LAB 01: Hello, Lua IoT!
--
-- This program blinks the on board LED, it is designed for the Huzzah Feather ESP8266 module.
--

-- Symbolic names for the pins
ONBOARD  = 3

-- Number of microseconds to leave the LED on
STAYLIT  = 250000 -- 1/4 second

-- Set the GPIO pin controlling the LED to output mode.
gpio.mode(ONBOARD, gpio.OUTPUT)

-- The flash_led function blinks the Green LED
function flash_led()
    -- LOW turns the LED on
    gpio.write(ONBOARD, gpio.LOW)
    -- We leave the LED on for 1/4 second
    tmr.delay(STAYLIT)       
    -- HIGH turns the LED off
    gpio.write(ONBOARD, gpio.HIGH)
end

-- Creates a timer 
--   Timer id = 1
--   Duration = 1000 microseconds (1 second)
--   Mode     = tmr.ALARM_AUTO (reregister to do it again forever)
--   Callback = flash_led
tmr.alarm(1, 1000, tmr.ALARM_AUTO, flash_led)

That’s all there is to it. Now you are ready to run the application.

Run the App on the Device

To run the application you will save it to the ESP8266, reset the device, then invoke the code.

Save the file, giving it a name: Lab01.lua
Press the button ‘Save to ESP’ on the lower left of the ESPlorer interface.
Push the reset button on the ES8266
When it’s done booting, click the ‘Reload’ button on the right side. You should see a list of files on the ESP8266
Double click the file on the right hand side that you saved. This should execute your code.

Wire the Huzzah Feather to the Power and Ground Rails

Connect the 3V pin to the Red column of holes marked with a ‘+’. Connect the GND pin to the Blue column of holes marked with a ‘-‘.

This image shows what it should look like:

Wire 3V and GND

Add a Three Color LED from the kit

Find the three color LED and the 560 Ohm resistors, then wire it up to pins 1, 2, 5 (aka 4, 5, 14 on the Huzzah) as the following images illustrate:

Connecting Resistors to LED

Then wire the LED to the power Rail, as shown here:

Connecting Power Rail to LED

Modify the code

Now that you have a three color LED wired to your ESP8266, you need to modify your Lua code to account for all of them. This code is modified to support the onboard LED and the new three colored LED you wired. Modify your code to match.

--
-- LAB 01: Hello, Lua IoT!
--
-- This program blinks an LED, it is designed for the Huzzah Feather
-- ESP8266 module.
--

-- Symbolic names for the pins
REDLED   = 1
GREENLED = 2
BLUELED  = 5
ONBOARD  = 3

-- Number of microseconds to leave the LED on
STAYLIT  = 250000 -- 1/4 second

-- Set the GPIO pins controlling the LED to output mode.
-- There are three pins, one each for: Red, Green, and Blue.
gpio.mode(REDLED,   gpio.OUTPUT)
gpio.mode(GREENLED, gpio.OUTPUT)
gpio.mode(BLUELED,  gpio.OUTPUT)
gpio.mode(ONBOARD,  gpio.OUTPUT)

-- The flash_led function blinks the Green LED
function flash_led()
    -- LOW turns the LED on
    gpio.write(REDLED, gpio.LOW)
    gpio.write(GREENLED, gpio.LOW)
    gpio.write(BLUELED, gpio.LOW)
    gpio.write(ONBOARD, gpio.LOW)
    -- We leave the LED on for 1/4 second
    tmr.delay(STAYLIT)       
    -- HIGH turns the LED off
    gpio.write(REDLED, gpio.HIGH)
    gpio.write(GREENLED, gpio.HIGH)
    gpio.write(BLUELED, gpio.HIGH)
    gpio.write(ONBOARD, gpio.HIGH)
end

-- Creates a timer 
--   Timer id = 1
--   Duration = 1000 microseconds (1 second)
--   Mode     = tmr.ALARM_AUTO (reregister to do it again forever)
--   Callback = flash_led
tmr.alarm(1, 1000, tmr.ALARM_AUTO, flash_led)

Run the Modified App on the Device

To run the application you will save it to the ESP8266, reset the device, then invoke the code.

Press the button ‘Save to ESP’ on the lower left of the ESPlorer interface.
Push the reset button on the ES8266
When it’s done booting, click the ‘Reload’ button on the right side. You should see a list of files on the ESP8266
Double click the file on the right hand side that you saved. This should execute your code.

Conclusion & Next Steps

Congratulations! You have built a Lua application that controlled a device connected to an ESP8266. The core concepts you’ve learned are:

Building a Lua application that can run on an ESP8266.

In the next lab, you will build a more complicated Thing that uses both input sensors and output devices.

Go to ‘Nightlight’ ›

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