Interfacing korry switches has also been a sticky subject. The problem OEM builders face – be it if you are interfacing Boeing 747, 737, or Airbus panels – is the amount of voltage, and current required to drive the indicator lights of the flight deck.
Interface boards on the market today (Arduino, FDS TEKWorx, Skalarki) are not built to drive original incandescent bulbs. These bulbs usually run at 5 VDC and require 0.115 A per bulb. Current can exceed over 20 amps when all panels are wired up and a light test (annuncaitors turned on) is performed.
Cockpit Builders have been able to bypass these limitations by using transistors. Simon was one of the earlier pioneers using a ULN2003A to ‘boost’ or ‘amplify’ the current required by the bulbs. Frustrated by the offerings in the market I also developed a an Arduino amplifier for output annunciation.
Fortunately our friend Captain Larsen (and guru electrical engineer!) also recognized these limitations and developed Korry LED Boards. I have now received a sample of the Korry LED Board and can report they work exceptionally well. For installation they are simple plug and play into the korry chamber.
With the LED boards installed, current to drive each korry chamber is now extremely low and annunciators can be controlled with available I/O solutions in the market. At 5V and using an Arduino Mega 2560 R3 board the annunciator are bright and easily visible.
At this time the LED board are only compatible with the newer type Korry switches but Captain Larsen tells me he is planning to also develop a PCB for the old type Korry switch.
* Does this eliminate the use of a ULN2003A transistor or an amplifier board? Not entirely so.
Despite the decrease power usage with each korry switch most I/O boards on the market are still limited by the total shared current sinkage. An Arduino Mega 2560 R3 board for example has a maximum of 200 mA output.
The specifications of the LED boards (2 LEDs)
White or Blue 10 mA
Green 1.1 mA
Amber 24 mA
If you are planning to use over 50 outputs on an Arduino board you will reach the maximum rate output. You can however overcome this limitation by using a ULN2003A transistor or an amplifier board.
Alternatively you can also try and spread the current load across several interface boards. One Arduino board can theoretically support up to 181 green LEDs, 20 white/blue LEDs or 8 amber LEDs.