USB Dew Point driver is included with libindi >= 1.5.0. Under Ubuntu, you can install the driver via:
sudo add-apt-repository ppa:mutlaqja/ppa
sudo apt-get update
sudo apt-get install libindi1
USB_Dewpoint calculates in real time the Dewpoint, thanks to ambiant humidity probe close to your instrument. It also connects to 2 external temperature probes (attached to tube or mirrors) and compares these temperatures to the Dewpoint. If temperatures too close to dewpoint it heats in a smooth or aggressive maner. We can also call it a heating regulator.
Second, if no heat required, USB_Dewpoint only uses 0.05W to run. It connects to computer USB (or HUB 2.0 / 1.1) to operate remotely and can be operated manually or in autonomy.
Main controls show information about current device state and allow for manual control of the power to the three output channels (0-100%). In automatic operating mode the values are essentially read-only as the device controls them itself based on temperature readings. Temperatures and humidity are read from the device every 10 seconds.
Values shown here are the device defaults which are restored if "Reset" button is pressed. All settings are automatically written to the device EEPROM so they are retained even if the device is used completely autonomously without computer.
Individual options do:
In automatic mode the device tries to keep channel temperature above dew point plus threshold like shown in this picture from the Windows driver manual (I think the equations are wrong way around, they should be Temp1-Dewpoint, but the idea is clear):
Before connection, you need to select the port. Usually, the port is like /dev/ttyACM0. USB_Dewpoint communicates via serial port at 9600 bauds, nothing special there. you can use udev-rule to create a pemement symlink:
$ sudoedit /etc/udev/rules.d/99-usbfocus.rules
Then write the following inside the file:
SUBSYSTEM=="tty", ATTRS{product}=="USB_Dewpoint"
Similar rule for USB_Focus would be:
SUBSYSTEM=="tty", ATTRS{product}=="USB_Focus", SYMLINK+="focuser", ENV{ID_MM_DEVICE_IGNORE}="1"
Then save the file, and restart your RPI3 or Computer and you should have symbolic links to your devices. For if USB_Dewpoint device is attached via USB, then you can use /dev/usb_dewpoint in your INDI driver.
There are no known bugs for this driver. If you found a bug, please report it at INDI's bug tracking system at Github.