Temperature display
This recipe implements a device with a locally attached LCD display to show time temperature and humidity from a BME680 sensor.
System Configuration
There is a configuration for the LCD display required. Here a HD44780 standard LCD display on the I2C bus is used.
- In the Device Element configuration the i2c pins must be specified. Here only these 2 properties are shown.
- The DisplayLCD Element is defined with the i2c address and LCD size.
- The NTPTime Element is used to retrieve the actual time from the default ntp server.
{
"device": {
"0": {
"i2c-scl": "D1",
"i2c-sda": "D2"
}
},
"displaylcd": {
"0": {
"description": "HD44780 LCD Display",
"address": "0x27",
"lines" : 2,
"columns" : 16
}
},
"ntptime": {
"0": {
"zone": "1",
"readtime": "04:00:00"
}
}
}This is specified typically in the env.json file that holds all the configurations for the board and the directly connected actors, sensors and displays. Samples for this configuration can be found in the description of the display elements and some board descriptions.
See also displays for a list of the supported displays.
Having done this configuration the display will also be used on system startup showing the device-name and the assigned ip-address.
Display elements
The configuration used 3 display elements for text to define the position and size of the information that will be shown:
Time events
Based on the time given from the NTPTime Element the Time Element creates an action every second to update the time displayed on the LCD.
BME680 sensor
The BME680 sensor measures the temperature and humidity every 10 seconds and sends actions whenever the values have changed. These are used to update the displaytext elements.
{
"displaytext": {
"time": {
"x": "0",
"y": "0"
},
"temp": {
"x": "0",
"y": "1",
"value": "--.--",
"postfix": "\u00dfC"
},
"hum": {
"x": "8",
"y": "1",
"value": "--.--",
"postfix": "%"
}
},
"time": {
"t": {
"description": "send actual time to displaytext",
"ontime": "displaytext/time?value=$v"
}
},
"bme680": {
"bd": {
"address": "0x77",
"readtime": "10s",
"ontemperature": "displaytext/temp?value=$v",
"onhumidity": "displaytext/hum?value=$v"
}
},
}