February 10, 2017

Troubleshooting Power Management Settings and Solving USB Disconnects

February 10, 2017/ Flaps 2 Approach

High-speed 5 volt powered USB hub. This hub resides in the Throttle Interface Module (TIM ). Note ferrite choke

Remember when all that was required to run flight simulator was one display monitor, joystick and a keyboard – those days are long gone.

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);

(viii) For multi USB connections use a quality powered USB hub; and,

(ix) Try to maintain space between USB cables and power cables.

Noise Limiting Node (NLN)

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.

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.

Power Requirements

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.

USB Hubs

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.

Recommended USB Hubs:

The USB hubs I use are Belkin powered 5 and 7 port USB hubs (Belkin F5U237-C). The C refers to the connector on he USB cable.

Screen grab of Windows 7 PMS. Windows 10 is similar

Windows Power Management Settings (PMS)

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.

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 generate ‘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).

A potential problem can be located with the USB cable, cleanliness and tightness of USB connections (including any USB hub), and loose wiring (especially if connectors have been used to secure the wiring).

Clean the USB connections with a quality cleaner to ensure cleanliness and make sure the USB connectors are tight. If the connectors need tightening, this can easily be done by pushing the small tabs inward on the female USB connection.

Final Call

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.

July 18, 2014

OEM 737-800 Lights Test Toggle Switch - Wired and Installed to MIP

July 18, 2014/ Flaps 2 Approach

OEM Lights Test Switch (before cleaning...) One switch comprising several switches

The lights test is an often misunderstood but simple procedure. The light test is carried out by the crew before each flight to determine if all the annunciators are operating correctly (illuminating). The crew will toggle the switch upward to lights test followed by a routine scan of each annunciator on the overhead, center pedestal and instrument panel. An inoperative light may preclude take off.

The lights test switch is a three-way switch which can be placed (and locked) in one of three positions; it is not a momentary switch. Toggling the switch upwards (lights test) illuminates all annunciators located in the MIP, forward and aft overhead and fire suppression panel (wheel well annunciator may not illuminate), while the central position (BRT) provides the brightest illumination for the annunciators (normal operation). Toggling the switch downwards activates the DIM function dimming the brightness by roughly half that observed when the toggle is in BRT mode.

Depending upon which manufacturer’s Main Instrument Panel (MIP) you are using, the toggle switch may not function this way. For example, Flight Deck Solutions (FDS) provide a three-way momentary toggle which is not the correct style of switch. You should not have to hold the toggle to light test as you make your pre-flight scan. The real toggle switch in the Boeing 737 aircraft is not a momentary switch.

Anatomy of the Toggle Switch

The OEM Light Test switch may appear to be a ‘glorified’ toggle switch with an aviation-sized price tag; however, there is a difference and a reason for this high price tag.

The switch although relatively simple in output, encompasses 18 (6+6+6) high amperage individual switches assigned to three terminals located on the rear of the switch. Each terminal can be used to connect to a particular aircraft system, and then to each other. This allows the toggle switch to turn on or off multiple aircraft systems during the light test.

The purpose of these multi-terminals is to allow the toggle switch to cater towards the high amperage flow of several dozen annunciators being turned on at any one time during the lights test, in addition to generators and other aircraft systems that are not simulated in Flight Simulator. In this way, the switch can share the amperage load that the annunciators draw when activated during the light test.

The switch can control the annunciators (korrys) for the MIP, forward overhead, aft overhead, fire suppression panel and any number of modules located in the center pedestal.

OEM Lights Test switch. The appearance of the OEM switch is not dissimilar to a normal toggle switch; however, the functionality is different in that there are a number of terminals on the rear of the switch to allow multi-system connection

Terminals, Interfacing and Connection

To determine the correct terminals to be used for the light test is no different to a normal toggle-style switch.

First, ascertain which of the six terminals correlate to the switch movement (toggle up, center and down). The three unused terminals are used to connect with other systems in the real aircraft (not used in Flight Simulator).

To determine the correct terminals for wiring, a multimeter is set to conductivity (beep) mode. Place one of the two multimeter prongs on a terminal and then place the other prong on the earth (common) terminal. Gently move the toggle. If you have the correct terminal for the position of the toggle, the multimeter will beep indicating an open circuit. The toggle switch does not require a power source, but power is required to illuminate the annunciators during the lights test.

For an overview of how to use a multimeter see this post - Flight Deck Builders Toolbox - Multimeter.

Daisy Chaining and Systems

Any annunciator can be connected to the light test function, and considering the number of annunciators that the light test function interrogates, it is apparent that you will soon have several dozen wires that need to be accommodated.

Rather than think of individual annunciators, it is easier to relate a group of like-minded components as a system. As such, depending upon your simulator set-up, you may have the MIP annunciators as one system, the overhead annunciators as another and the fire suppression panel and modules mounted in the center pedestal as yet another. If these components are daisy chained together (1+1+11+1+1=connection), only one power wire will be required to be connected at the end of the array. This minimises the amount of wire required and makes connection easier with the toggle switch.

Two Methods to Connect to the Switch

There are two ways to wire the switch; either through the flight avionics software (software-based solution), or as a stand-alone mechanical system. There is no particular benefit to either system. The software solution triggers the Lights Test by opening the circuit on the I/O cards that are attached to the computer, while, the mechanical system replicates how it is done in the real Boring aircraft.

Switch in-line (software connection using ProSim737)

The on/off terminal of the toggle switch is connected to a Leo Bodnar card or other suitable card (I use a Flight Deck Solutions System card), and the card’s USB cable connected to the main computer. Once the card is connected, the avionics suite software (ProSim737) will automatically register the card with to allow configuration. Depending upon the type of card used, registration of the inputs and outputs for the card may first need to be registered in Windows (if using Windows 7 type into the search bar joystick and select calibration).

To configure the toggle switch in ProSim737, open the configuration/switches tab and scroll downward until you find the lights test function. Open the tab beside the name; select the appropriate interface card (Leo Bodnar card) from the drop down menu and save the configuration.

ProSim737 will automatically scan the interface cards that are installed, and if there is a card that has a power requirement, such as a Phidget 0/16/16 card (used to convert OEM annunciators, modules and panels), the software will make a connection enabling the lights test to function.

Considering the connection is accomplished within the ProSim737 software, it stands to reason the lights test will only operate when ProSim737 is open.

To illuminate the annunciators when the switch is thrown, a 28 volt power supply will need to be connected to the annunciators either separately or in a daisy chain array.

OEM aviation relay mounted in center pedestal

Stand-alone (mechanical connection)

The second method, which is the way it is done in the real aircraft, is to use an OEM 50 amp 6 pull/6 throw relay device.

Depending upon the type of relay device used (there are several types), it may be possible to connect up to three systems to the one relay.

Lights Test Busbar

Although the Lights Test switch has the capacity to connect several systems to the switch itself, it would be unmanageable to attempt to connect each panel to the lights test switch.

To solve this issue a centrally-placed aviation-grade relay has been used in association with a busbar.

A benefit of using an OEM relay and busbar is that the relay acts as a central point for all wires to attach. The wires from the various systems (panels, korrys, etc) attach to the busbar which in turn connects to the various posts on the relay.

The relay will then open or close the relay enabling power to reach the annunciators (via the busbar) when the switch is positioned to Lights Test.

The stand-alone system will enable the lights test to be carried out without ProSim737 being open.

Although the relay is not large (size of a small entree plate), it can be problematic finding a suitable area in which to mount the relay where it is out of the way. A good location is to mount the relay inside the pedestal bay either directly to the platform floor or to a wooden flat board that is screwed to the lower section of the center pedestal.

Using the DIM Functionality (toggle thrown downwards)

This post has only discussed the lights test. The DIM switch is used to dim the OEM annunciators (korrys) for night work.