Disclaimer: the experiences described here are my personal opinion. I bought the product privately directly from the manufacturer and paid for it myself.
In the meantime, I often have the situation of having to switch between different computers, e.g. laptop and PC or PC and Raspberry Pi. Monitors usually offer several inputs, so switching here is usually not a problem. However, there is still the problem of having to move the keyboard and mouse around as well, which can be very cumbersome in the case of stationary PCs under the desk.
The solution: a KVM switch. KVM stands for “Keyboard Video Mouse”. Such a switch is connected to a monitor, keyboard and mouse and forwards the connection to one of several connected computers. I chose a model from TESmart, which allows it to be mounted on a wall or under the desk. Furthermore, it also offers practical functions such as “USB passthrough”, which are often missing in simpler models. There are also models that are intended as a desktop device, but otherwise work in the same way.
Scope of delivery
In addition to a plug-in power supply (5V, 2A), a complete cable set with four HDMI and USB connections to the individual computers is included in the scope of delivery. There is also an infrared remote control, but you still have to buy batteries (2× AAA) for this, as these are not included in order to make shipping easier.
There is one HDMI and one USB 2 upstream port for connecting the computers. For the monitor and input devices, there is one HDMI and two USB 2 ports for the keyboard and mouse, which are also specially designed for this. For example, keyboard shortcuts for operating the KVM switch itself are only recognized via these connections. In addition, there is another USB port that can be used for another device, such as a webcam, which works for me with a Logitech C920 without any problems. USB 3 is not supported, but this is not necessary for the intended area of application.
Keyboard and mouse emulation
Simpler KVM switches emulate a standard PC keyboard and mouse and only interpret the input from the connected input devices. However, this means that additional keys such as multimedia controls on the keyboard or additional keys on the mouse are often unusable. Sometimes wireless connections with special USB adapters are not supported. For example, Delock writes about its KVM switch at https://www.delock.de/produkt/11483/Features.html?setLanguage=en, quote:
KVMs emulate a standard wired 104 key keyboard and wired generic 2 or 3 button scroll wheel mouse on their respective console ports. Whether or not a wireless or gaming mouse and keyboard work with KVM switches depends on several factors; in general, most wireless mice and keyboards do not support working with KVM switches. We recommend to use a standard wired mouse and keyboard with our KVM switches.
Fortunately, this is not the case with TESmart’s KVM switches such as the HKS0401B2U-EUBK. They offer a “USB passthrough” mode that allows unrestricted use of both wireless devices and additional functions.
Passing on the EDID data
EDID stands for “Extended Display Identification Data”. This allows monitors to provide the computer with data about the resolution and frame rate. This data is used to adapt the maximum resolution of the graphics card to the capabilities of the monitor.
The TESmart model forwards data from the connected monitor to all computers, regardless of whether they are selected as the active device or not. As a result, the set screen resolution in particular remains unchanged and windows on the desktop are not moved or changed in size unintentionally.
The device has an infrared remote control, which I personally don’t need after installing the device under the desk.
The HKS0401B2U-EUBK is designed to be mounted on the wall or under the desk. It is therefore not always easy to operate the device itself. But the solution for this is convincing: you can also switch directly via the keyboard using keyboard shortcuts. With TESmart, you press the “Scroll Lock” twice and then either the number of the desired input (with a 4-way switch then 1 to 4) or “Page Up” or “Page Down” to change the input. This option also applies to most other TESmart models.
If desired, you can also activate an acoustic feedback.
Switching with the mouse
I personally don’t use this option, but for the sake of completeness it should be mentioned: you can also change the monitor by “tapping” twice on the edge of the monitor with the mouse pointer. The KVM switch recognizes the movement of the mouse pointer briefly moving back and forth horizontally and then changes depending on whether you “knock” to the left or right. By default, however, this function is switched off so that you don’t accidentally switch monitors. If the mouse movement is not reliably detected, you can also increase the sensitivity with a button on the device.
Based on my personal experience with it, I can recommend the TESmart KVM switch. Switching between the computers is smooth and fast (about 2 seconds switching time with keyboard shortcuts) and the webcam (Logitech C920) can also be used without restriction on all connected computers. The specified maximum resolution of 3840×2160 at 60 Hz also works as advertised.
By mounting the switch under the desk, no additional space is required on the table and the necessary cabling can be done inconspicuously. If needed, the laptop is connected with a HDMI/USB cable and power supply. A USB-C dock with connections for HDMI/USB would also be possible, which would make everyday use even easier. A Raspberry Pi can also be used without any problems, although you may have to use your own cables or an adapter, as newer models use a micro-HDMI connection and USB-C.