LEFT: High-speed 5 volt powered USB hub. This hub resides in the Throttle Interface Module (TIM). Note ferrite choke. (click to enlarge).
Depending upon the level of system complexity, a flight simulator may require a dozen or more ports to connect peripheral items to a server or client computer (s). Historically, connection of peripherals has been via USB.
USB is an acronym for Universal Serial Bus and, generally speaking, if only a few peripherals are attached to a computer, there usually is not a problem with communication between the computer and the attached device. However, as interface cards and peripherals become more complicated and numerous, there is a propensity for disconnects to occur more frequently. A USB disconnect usually announces itself by the sound card playing the ‘ding-dong’ sound as the peripheral disconnects itself from the computer.
Guidelines (golden rules)
There are several ‘golden rules’ to remember when using USB.
(i) Try and keep all USB cables as short as possible;
(ii) Do not join USB cables together;
(iii) Always use quality USB cables with quality connectors;
(iv) Do not ‘kink’ the USB cable or wrap the cable so tightly that the wires are at a 90-degree angle;
(v) Do not lie USB cables beside one another so they are touching, but maintain some space between them;
(vi) Use a USB cable fitted with noise limiting nodes (NLN);
(vii) Use a USB cable/port that is rated at the highest output (USB 3 or above); and,
(viii) Where possible for multi USB connections use a quality powered USB hub.
A noise limiting node (NLN), also known as a 'ferrite choke' is a small cylindrical node that sits at each end of a USB cable. Briefly explained the nodes are made from a solid ball of ferrite which is magnetic and therefore quite heavy.
LEFT: Ferrite choke on USB cable.
The purpose of the NLN is to stop electromagnetic interference (EMI) transferring from the peripheral to the computer. EMI can be produced from any number of peripheral items and a USB cable running between the peripheral and the computer acts as an antenna, picking up and transmitting EMI current. The current can, but not necessarily always, cause havoc with either the operation of the peripheral or the computer itself.
Adding USB Ports
As the number of add-on peripherals increase, the number of available ports falls short and additional USB ports need to be added to the computer. Additional ports can easily be added to a computer via a PCE card which enables (on average) an additional 4 USB ports to be added to your computer. A PCI card is attached to your motherboard.
One of the main reasons that USB disconnects occur, relates to the power that is available to the computer’s USB port. Often the power requirements of the device will be greater than that provided to the USB port; this causes a disconnect. Additionally, depending upon your computer, it is not uncommon for power to fluctuate between USB ports as the computer’s motherboard directs power to various processes.
Depending upon how your system is set-up, when several devices 'come on line' a minor spike can be generated. Often, this spike can momentarily exceed the amperage rating of the USB port. This can cause a disconnect to occur.
It’s important to understand that not all USB ports are made identical. In general, the ports on the rear of the computer are part of the computer’s motherboard; these ports are rated as high power ports. However, USB ports that are not part of the motherboard, and usually located on the front of the computer may not receive the same power rating.
Often a supply company will provide a computer will a dozen or so USB ports, however, to save money will choose to use what is called a ‘front panel USB header’ which has a small piece of circuitry that acts as a hub. In this case, the power to the front panel USB is reduced. Furthermore, it is probable that these ports may not be USB 3 and if used for a high-demand peripheral will cause a disconnects to occur.
Another strong recommendation is to use a high quality powered USB hub rather than connecting several USB cables directly to a computer. A powered hub should be used rather than an unpowered hub as the former provides its own direct power source which is usually rated at a higher amperage than the computer’s USB port.
The interface modules that form the core of my simulation system have one or two powered hubs installed to the module. The interface cards are then connected by very short USB cables to the hub. A high quality USB cable (with a NLN) then connects the interface module directly to the computer.
Not all USB peripherals will be required at all times. Often a device will not need to communicate with the computer until something is required – such as a change to a radio frequency, an input from the control column or a key press to the MCP or CDU.
LEFT: Screen grab of Windows 7 PMS (click to enlarge).
Windows has a nasty habit of ‘putting to sleep’ a USB connection that is not being used. It does this to save power. It is very imperative that you ensure that all power saving modes are turned off with regard to USB.
To do this open your control panel and search for device manager. Scroll down until you find Universal Serial Bus. Under this tab you will find all the USB ports that you have attached to your computer. Open each in turn and check the power management settings and ensure they are turned off.
Troubleshooting USB Disconnects
It is paramount to try and discover which peripheral is causing the disconnect. The easiest way to troubleshoot a disconnect issue is to remove ALL the USB cables from the computer, and then one by one re-connect the cables to the allocated port and test. Make sure you switch your computer off and on as you add each of the cables in turn. Hopefully, you will eventually discover which cable/device is causing the issue. The problem device will ‘ding dong’ if a secure connection is not possible.
If USB disconnects continue, try swapping the cables between different USB ports on the computer. The disconnect issue maybe caused by the USB port/cable combination you are using. As mentioned, not all USB ports have the same amount of power/amps available to them.
Try to place peripherals that require minimal power, such as a mouse or keyboard, on lower-powered USB ports, and place more energy-requiring peripherals on powered hubs; perhaps only a few devices on the one hub. Doing this will ensure that the hub will always have enough power (amps) to power the devices attached (cancelling out possible spikes as discussed above).
Hopefully, if you apply the above-mentioned suggestions USB disconnects will cease. However, you will eventually reach the limit of USB capability, and at this point the use of Ethernet should be investigated to augment, or to replace the reliance on USB.
This article is but a primer. I am not an IT expert and welcome any comments.