I wired up the remaining annunciator lights (other than the “Canopy Unsafe” light). The final three were the landing and taxi lights as well as the fuel pump. Unfortunately, this unveiled a flaw in the annunciator control circuit I designed. Basically, for annunciator lights that are triggered high, I was assuming the transistor base voltage would be shed through the load when the load was turned off. The problem is that for certain types of loads (e.g. LED lights), the load resistance is pretty high at low voltages. This has the effect of causing the transistor base voltage to fall pretty slowly after the load is turned off, which causes the annunciator light to dim slowly. I really need to couple the base and emitter with a resistor to provide an alternate path for the base voltage to drain. I’ll have to redesign the circuit and have new PCBs made.
