March 22

Droplet External Device Support – Serial/COM/LPT Ports (Part 1)

For some time, we have supported external devices, and this comes in a couple of flavors connected to a couple of different use cases. We support COM/Serial/LPT redirection, USB redirection, and PCI pass-through*.

Serial/COM/LPT Redirection

The most common use of our native COM/Serial/LPT port redirection seems to be in engineering environments connected with aviation, automotive, and process management. Frequently these dedicated systems need an engineer to run periodic diagnostic or maintenance tasks, where connectivity is provided by a COM/serial port or LPT port on the device itself. Of course, it’s been some years since many laptops even had COM ports, so in most cases, a USB to Serial dongle is needed to provide the physical connectivity. For lab environments using a fixed desktop or tower PCs, there is still the option to purchase PCI cards that fit to the riser and provide either single or dual-port serial interfaces. In some of our higher-end engineering customers, the device that needs to be tested or serviced has a dual serial/com ports. These COM/Serial to USB devices are largely manufactured in the far east and are inexpensive, however, for that reason, their quality varies significantly. We have had a very good experience with the StarTech range of devices, and their backup documentation is reassuring – as they appeared to be are aimed at the engineering sector.

The good news is Droplet 2.x natively supports these COM/Serial/LPT devices. The functionality is built-in and merely needs turning on from the settings.json file which can be found manufactured C:\Users\%username%\AppData\Roaming\Droplet in the per-user mode, and in C:\ProgramData\Droplet in the service mode. All you need to do is modify the settings.json in notepad, and then restart the application or service for it to take effect:

In terms of the Serial/COM/LPT port ID which is usually represented by a number (COM1, COM2, and so on) whatever that port number is in on the Windows PC it will be the same number in the container. Occasionally, this com port number on the Window PC will need to be adjusted if the application is hard to code to only utilize COM1 or COM2)

This can be tricky especially if the remnants of “phantom devices” are already occupying those slots. I’ve found showing “hidden device” in Device Manager is helpful when troubleshooting this.

When I demo this in my lab to customers, I use an old APAC PDU which has a serial port on the rear and PuTTy inside the container using its com port option to act as the terminal emulator:

Note: Just look at that 1997. God, how young were you in 1997? Where you even born? Shudder…

So, the moral of this story is – you don’t need the UBS edition of our software to connect a USB-to-Serial/COM/LPT dongle to the container – that’s is a built-in of Droplet. The only thing you might have to worry about is the driver install on the Windows 10 PC and messing with the device ID to work with your software.

In the next episode, I will look at our USB support and how that works…

* PCI pass-through is currently only supported with the Linux edition of our software and requires a modest amount of free support to get it set up and running


Copyright 2021. All rights reserved.

Posted March 22, 2021 by Michelle Laverick in category "Droplet Computing