Hi @rmoscoloni, this is because our initial ESP8266 support guides you through adding the device as a 'Bring Your Own Thing'/MQTT device rather that the Arduino or Raspberry Pi options you might have used on Cayenne previously.
It's by design that that you can't add something like the DS18B20 because the process for adding sensors is different for MQTT devices. Rather than choosing a sensor like DS18B20 from Add New > Device/Widget > Sensors > etc, you publish the sensor data to Cayenne on a channel and we will automatically create the widget on your dashboard, which you can then manipulate as you please.
Here are some real examples from the ESP8266.ino sketch we provide when adding the device:
Cayenne.virtualWrite(3, 50, TYPE_PROXIMITY, UNIT_CENTIMETER);
Each of these when executed will publish data to Cayenne on the selected channel, and create a widget based on the data type. This is what it looks like with those 3 in place:
Those are passing the static values of 22.0, 700, 50, of course. For a real world sensor you would want that parameter to be a variable or call to a function that reads your actual sensor.
Please note that you can, however, add Custom Widgets to MQTT devices, you just have to point them to a channel, and then use statements like above to populate them with data.