Computers, network devices, peripherals, electronics, all of them need power supply to work. You’ll have to ensure that every device is properly powered, which may be not trivial.

Some devices provide their own means of power supply. They typically provide a power cable or an external power supply you can plug in a power socket. That’s the case of computers, speakers, monitors, etc. But some other devices expect you to provide a determined voltage of DC current by your own. Arduino boards, electronic boards, frameless screens, are some examples.

The thing is even harder if you consider more complicated things as the lighting of your cockpit. Any realistic cockpit have backlighted panels, which are limited by a rotary in some control panel as the real aircraft does. That’s another dimmed power circuit you’ll have to isolate from the rest.

Power supplying is not brain surgery. But there are some guidelines that may be useful.

Power Supply Units

An ATX PSU
An ATX PSU

As mentioned above, there are some cockpit elements that are trivially powered thanks to its own internal or external power supply. Just connect them to a power strip which supports enough electric power for the devices you want to connect. It is highly recommended to choose one with circuit breaker to avoid current overload, and a on-off switch that let’s you disconnect it when the cockpit is not used.

For anything else, like Arduino boards, panel boards, panel backlighting, auxiliary lights, etc, the most simple and affordable solution is to use ATX PSUs.

Any modern desktop personal computer integrates a standardized power supply unit, or PSU. The PSU converts the AC input of your home to DC outputs of different voltages into multiple standard connectors designed for the motherboard and peripherals of the PC. From them, the most interesting for us are the IDE (Molex) or SATA power connectors. They are comprised by four lines: 1 of 12v, 1 of 5v and 2 ground lines. They are perfect for the inputs we require in our cockpit:

A Molex connector with 12v, 5v and GND lines.
A Molex connector with 12, 5 and GND lines.
  • 12v to power the backlighting circuit.
  • 12v to power small monitors for the glass cockpit
  • 5v to power the electronic devices as Arduino boards and some integrated circuits.

The PSU can source these voltages without requiring the rest of connectors to be connected to any PC. You only have to take one thing into account: modern PSUs have no power up button. They are designed to be powered up by request of the motherboard through the ATX power connector. More precisely, the pin 16 is pulled-up to 5v by the PSU. The motherboard have to drive it down to GND to indicate the PSU it must be powered up. Thus, if you want to power up your PSU, you only have to put a cable from pin 16 to any other pin providing GND (e.g., 15 or 17). Check this Wikipedia article for more details.

Perhaps you are wondering how many PSUs you need. A precise and optimum number could be really hard to calculate. Because of backlighting, the power consumption is not minor. Each PSU supports a maximum power connected to each of its circuits. And it is vendor-dependent. In this case, it is better off to have enough PSUs to be really close from that maximum power. With three PSUs (one for pedestal, one for glareshield and one for overhead) you will have enough power for all the circuits.

Backlight circuit and dimmers

A 12v dimmer for backlighting
A 12v dimmer for backlighting

As mentioned above, the backlight circuit is passed through a dimmer controlled by a rotary control somewhere in the cockpit. In A320, there are separated circuits for pedestal, glareshield and overhead. Each one have its own rotary control so their luminosity can be set separately.

There are many dimmers available in the market that may be used in your cockpit. The cheapest and simplest option is to acquire one of them from any electronics retailer. The dimmer circuit, with its rotary potentiometer, is typically included into a case so you only have to connect the wires using screw connectors (see attached figure). But obviously you don’t want such cases in your cockpit. You’ll have to disassemble the case and extract the dimmer board and its potentiometer. Then, you can place the rotary in the corresponding cockpit panel and leave the board behind it.

Dimmer electronic boards connected to pedestal lighting panel
Dimmer electronic boards connected to pedestal lighting panel

One important thing about the dimmers is that they dim the light by reducing the voltage between its two terminals. It has two input lines and two output lines. The inputs are 12v and GND, and the output lines are undetermined. You can count that voltage difference between two outputs is 12v when dimmer is at minimum, 0v when it is at maximum, and some intermediate value in the middle. But none of its outputs are warrantied to be 0v respect GND. This have a very important consequence: you cannot mix the GND lines with the negative line of your dimmer output. Do not thing on such negative output as GND but as DGND (dimmed GND), or the positive output as 12v but as D12V (dimmed 12V).

Power Distribution Board

OAC Power Distribution Board
OAC Power Distribution Board

Connecting the PSU outputs directly to the elements could be complicated and messy. A single PSU provides about 4 or 5 IDE or SATA power connectors. That’s indeed not enough to power all the devices you want to connect. So you need a way to distribute the power across devices.

Open Airbus Cockpit uses a electronic board known as Power Distribution Board. This board is designed to connect a pair of IDE connectors as input, and as many needed devices as outputs. It is also designed to connect the 12V power line to the corresponding dimmer and obtain the dimmed power line as input, so devices can consume the dimmed power line for backlighting.

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