This project includes Arduino code for the thermometer device, and AWS Lambda code for the Alexa Skill
You'll find directions on getting everything set up at Hackster.io
A temperature probe with a display can be controlled through Alexa:
- choose a food to cook and the high or low alarm temperatures are set automatically
- the probe displays the current step, the temperature and set point, and alerts the user when the heat should be adjusted or shut off
- Alexa can supply the current status at any time
The thermometer has one or more thermometer probes, for measuring liquid and food and oven temperatures. It also has an audio annunciator (buzzer) and a visual one (neopixel LED), and a button to shut off the alarms.
Most importantly, the microcontroller in the device can connect to WiFi, and has the key and secret for a very limited IoT user. This allows the device to connect to MQTT topics in the AWS cloud and report its state (temperature, set points, current step) and react to the Alexa skill's desired state (controlling the thermometer).
The Alexa skill is a custom skill that permits a user to request that a recipe be started, or to control the stage of the recipe The skill requires the user to link their account to be able to identify the devices the user owns. In this code, we've hardcoded some of those settings.
The skills' Lambda code can look up a user id in a DynamoDB table and obtain the user's Thing ID. It also can look up the user's state in another table, so that Alexa knows a recipe is in progresss when the user starts talking to Alexa after the recipe's been underway for a while.
The AWS Cloud has a shadow state for each device, showing what the current and desired states of the Thing (device, in our case the thermometer) are. The Alexa Lambda code can access this or change the desired device state in response to user interactions, depending on the User state. The MQTT topics allow the device to constantly be aware of changes without Alexa code needing to locate and communicate directly with the device.
A JSON file contains all the recipes the Alexa Skill can handle, with steps, and thermometer setpoints and dialog info for each step. A summary version of this is in a public S3 bucket and available to the device by requesting a URL. The device checks this URL and compares the ETAG with a copy of the file stored in the device's filesytem area of FLASH (called SPIFFS). It checks and updates the file if necessary only when the device powers on, but has access to the data when new desired state commands arrive from the MQTT topic.
The device regularly reads the probe temperature(s), looks for changes, and then updates its display and the Thing Shadow. It also monitors the shadow's Delta topic, reacting to new commands - start a recipe or go to the next recipe step. It uses the JSON data in the recipes file to know which temperature setpoints to set and what text to display.
The device is actually composed of two separately programmed microcontrollers:
- an Adafruit HUZZAH ESP8266 handles the WiFi, AWS connection, recipe logic, and the e-paper display
- an Arduino Uno (you can use a smaller device, this is what I had on hand) is an I2C slave controlled by the ESP8266, and handles thermometer readings, beeping, flashing, and such peripheral things.
Why two controllers? This is not an uncommon pattern for embedded design, but because we chose an ESP8266 to handle the WiFi, we wind up with few available ports for the thermometers. We'll need a couple of analog ports and few pins to handle the buzzer, buttons, and multiple thermometers.
The Arduino Uno supports Slave Mode on the I2C bus. I'd originally targeted the low power and powerful Arduino MKRZERO, but it turns out the I2C libraries for the SAMD processor haven't yet implemented I2C slave mode.
"Alexa, ask my thermometer to make Yogurt"
"Alexa, ask my thermometer for the status"
- an AWS account
- an Amazon Developer account
- ESP8266 device, such as Adafruit HUZZAH or Wemos D1 Mini
- Arduino Uno (or another Arduino that supports I2C slave mode)
- USB programming cable (usually, a micro-usb DATA cable)
- E-paper display, I am using a 1.54" red-black-white display, you can also use oLED, or omit the display
- DS18B20 thermometer probe (for immersion) and 4.7K ohm resistor
- thermocouple probe (for bbq & oven) (future, not implemented here) and resistors
- piezo buzzer (to alert someone) and 100 ohm resistor
- momentary (Normally Open) pushbutton (user can silence alarm) and 10k ohm resistor
- neopixel (status and to alert someone) (I used an 8-pixel ring)
- breadboard and wires
| Peripheral | PIN | ESP8266 Pin |
|---|---|---|
| Waveshare 1.54" e-paper | 3.3v | 3.3v |
| " | GND | GND |
| " | DIN | GPIO13 |
| " | CLK | GPIO14 |
| " | CS | GPIO15 |
| " | DC | GPIO0 |
| " | RST | GPIO2 |
| " | BUSY | GPIO12 |
| Uno I2C | SDA | SDA (GPIO4) |
| " | SCK | SCK (GPIO5) |
| " | GND | GND |
| Peripheral | PIN | Arduino Pin |
|---|---|---|
| NeoPixel Ring | VIN | VCC (+5V) |
| " | GND | GND |
| " | Data In | Digital pin 6 |
| Piezo Buzzer | + | Through 100 ohm resistor to digital pin 9 |
| " | GND | GND |
| Momentary Push Button | A | through 10k ohm resistor to GND |
| " | A | directly to digital pin 12 |
| " | B (the other leg) | VCC (+5V) |
| DS18B20 | black | GND |
| " | red | VCC (+5V) |
| " | yellow | directly to digital pin 10 |
| 4.7K resistor | needed for DS18B20 | between pin 10 and VCC |
- The Arduino IDE (latest version)
- Adafruit GFX
- Adafruit Sensors
- Dallas Temperature library
- GxEPD e-paper (if using a display)
- AWS Websocket MQTT Client (and the libraries it requires)
- ArduinoJSON
- ESP8266 hardware libraries
See Hackster.io for a build walkthrough