For almost everything that can happen to the different systems of a commercial plane, there is an annunciator light. They tell the pilot if a valve is open, closed or in transition. They inform him about important conditions like low pressure in the fuel system. They draw his attention to and help him locate possible problems. They are indispensable for the management of the plan. And there are many of them…
I tried to build annunciators that are similar to those found in the cockpit of the B-737. As a light source I selected Spider LEDs because of their brightness and wide viewing angle of 90 degrees.
A Coel Draw design of the annunciator. Again, the main material is acrylic glass. All parts are joined with Super Glue.
Black = black acrylic
Green = transparent acrylic
Orange = PCB for mounting the LED
Production has started!
Gluing the five layers together with Super Glue is a rather messy process, but I could not figgure out any better way. Since the walls of the annunciators are just 1mm thick, they sometimes bend during laser cutting. For multiple annunciator housings it might be necesary to add thin, black carboard on the inside to avoid the spilling of light from one compartent to the next (i.e. a second annunciators being partially lit by it’s neighbour).
This picture shows parts for the annunciators in the Warning Panel. They are different from the others, both in size and because they are part of push buttons with reset (or recall) functions.
The transparent acrylic plates are inserted into the black frames and glued in with Super Glue. Once the glue bonds completely, the side that will face upwards is sanded to achieve a completely flush surface.
The sanding changes the surface of the acrylic glass from glossy to matt and ranslucent. This is desired, because it helps to distribute the light from the LED more evenly.
Corel design for a two state annunciator. In the B737 cockpit, all annunciators that show the state of valves have two states (valve closed = Off, valve in transition = bright, valve open = dimm).
I could not fit two spider LEDs inside the annunciator case, so I used two superbright 3mm LEDs. They have a relatively small opening angle. But when tilted correctly, they light the annunciator surface quite evenly.
Installation of the LEDs on the PCB. They are glued into the annunciator cased with two drops of Super Glue. This fixes them well enough and allows for easy removal if one of the LEDs needs to be changed.
Plenty of annunciators in this panel!
The lables that are printed on the translucent foil have low contrast when the LEDs are off. This is intentional to help improve the readability of the panel.
The guide for the lever, made from several layers of transparent, 3mm acrylic glass. Note the irregular indents on the lower side. Here is where the ball bearing of the plunger rolls along. Since the plunger is spring loaded, there is clear tactile feedbeck when the top of the ball bearing sinks into any of the indents.
The two claw-shaped spaces will later hold microswitches that sense when the lever has reached its max. or min. position.
Three Spider LEDs are already glued into the openings in the upper part of the guide.