Korry annunciators on the Airbus flight deck operate on 5 volts – this voltage allows for bright illumination and good visibility of the korry switches during daytime operations. However, when operating the aircraft at night, the korrys at this intensity can be overwhelming and distracting. With continuous usage the incandescent bulbs can also dissipate a significant amount of heat making them hot to touch.
Airbus (and other aircraft manufacturers) understand the significant of having a dimming function in the cockpit. The dimming switch, accessible on the overhead lighting panel, is integrated into a 3 pole switch – TEST – BRT -DIM.
Switching to the dim position switches the korrys to a lower operating voltage.
There are several ways to implement a dimming function to the korry annunciators in a simulator – pulse width modulation (PWM) or using a hardware or software controlled relay.
Using PWM is an elegant solution but requires the outputs of the simulator to be connected to an interface board which supports this function. Alternatively the dimming of the korry outputs can be driven and switched by a hardware relay (explained extensively here at Flaps 2 Approach), or by a software controlled relay.
A software controlled relay approach was elected as this can allow for the dimming function to be implemented and executed at seperate nodes on the flight deck. Multiple relays can be installed to reduce a single point of failure, and also distribute current around the main instrument panel, pedestal and overhead.
Songle (SLA-05VDC-SL-C) 30A relays can be purchased on e-commerce platforms such as Aliexpress for a few dollars and meet the high current switching requirements. A Mean Well (LRS-350-3.3) 3.3V 60 amp power supply unit can be used to fulfil the dimmed power requirements for the korrys on the flight deck. A minimum of 3.3V is required for LED korry annunciation.
Simply assign the relay to the DIM switch in your avionics program. The Common (COM) contact outputs to the korrys in the simulator. The Normally Open (NO) terminal connects to 3.3 V PSU, and the Normally Connected (NC) terminal connects to 5 V.