Panel Backlighting: Option B

[erikscott128]

Summary:

The existing backlighting method utilizes a multi-layer method that can be accomplished entirely using a laser cutter (and a manufactured PCB). While it provides good results, there are several issues associated with this design. A method more in-line with what is done on actual panels provides several significant benefits at the expense of slightly more difficult fabrication.

Current Method ("Option A"):

Overview:

The current backlighting method divides the panel into 4 layers. The top-most layer, referred to as the "legend plate" is a laser-engravable material consisting of a thin black upper surface and translucent white body. Panel legends and insignia are laser-engraved on the upper surface such that the white material is revealed. The second layer, referred to as the "light plate", is a translucent white acrylic layer used to diffuse light within the panel. The third layer is an opaque black acrylic layer, referred to as the "backplate", to which most switches, buttons and other panel components mount. Below that is the backlighting PCB, which contains connectors and a capacitor on its lower side, and addressable RGB SMD LEDs (red-green-blue, surface-mounted light-emitting diodes) on its upper surface. The LEDs are recessed in cutouts within the backplate. They shine up into the translucent light plate and the light ultimately escapes through the engravings in the upper surface of the legend plate, or is absorbed within the light plate or legend plate. The LEDs are positioned directly below the engraved labels, and are packed densely to provide even light distribution and avoid so-called "hot-spots" (distinctly bright areas) of the appearance of the backlighting. The individually addressable LEDs provide the ability to dim or brighten specific LEDs to further reduce hot-spots. Because of the number of LEDs and the relative density of the engraved areas on the legend plate on most panels, the number and size of the recesses required on the backplate become fairly extensive, resulting in a "swiss-cheesed" look of the backplate, which reduces the strength of this layer. This issue is largely mitigated by the strength provided by the other layers. The backplate must also be thick enough to accommodate the LEDs, usually necessitating 1/8" or 3mm thick acrylic. This is in addition to the thickness of the backlighting PCB, which is at least 1mm for reasonably-priced custom boards. The entire stack-up is held together with No. 6-32 screws. The edges of the legend plate and light plate must be manually painted black to prevent light-leakage. The light and legend plates can be optionally fused together to make a single panel similar to the light plates found in actual aircraft (see the real-life implementation section for details).

Benefits:

This method was devised by @L-Walker and has several benefits. Chief among these is the relative ease of construction, provided the builder has the appropriate materials and access to a laser cutter/engraver. The PCBs can be manufactured relatively cheaply from PCB manufacturing houses like JLCPCB with SMDs and connectors already soldered to the board. With each layer fabricated, the builder need only mount the switched to the backplate and backlighting PCBs and assemble the rest of the sandwich using No. 6 screws after painting the edges of the light and legend plates.

The individually addressable LEDs provide the ability to tune the brightness of specific LEDs to help eliminate hot-spots. Additionally the ability to flash the legends associated with a specific switch can help utilize the sim-pit as a training device, or help identify a switch during the setup phase.

Disadvantages:

The necessity to use a 1/8" or 3mm backplate, plus the minimum 1mm backlighting PCB thickness results in a ~4mm thick panel for switches to mount to. The threaded bushing on many switches does not allow for this with sufficient thread engagement of the associated mounting nuts. Sometimes, even if sufficient thread does exist, the shafts of potentiometers, encoders, and rotary switches does not protrude high enough above the legend plate and into the associated knob to permit the set screws to grip the shaft. This limits the selection of switches available to use in the designs of panels and sometimes required the modification of knobs to re-position set-screws.

The requirement that the LEDs be recessed in the backplate requires that extensive amounts of the backplate be removed, resulting in the afore-mentioned "swiss cheesed look. This can potentially make the backplate relatively fragile and prone to breakage during assembly. Once assembled, however, this fragility is largely mitigated by the structure provided by the solid PCB from below and solid light and legend plates above.

The large amounts of space required by the LEDs, and the fact that the PCB is located below the light plate limits mounting options for switches, stand-offs, and more complex assemblies on the underside of the panel. Since screws cannot penetrate through areas located where LEDs are, and LEDs are located wherever legends are placed on the upper surface, mounting positions are very limited, especially on compact, non-standard panels such as the LDG GEAR panel.

Because the light-plate is translucent rather than transparent, light does not travel very far within the panel before being absorbed. This requires an extensive number of LEDs. This makes PCBs more expensive, presents potential power consumption issues, and exacerbates the issues presented above regarding backplate swiss-cheesing and mounting space.

Real-life implementation:

Overview:

The specs for real-world panels can be found in MS25212. In short, they consist of an upper plastic "light plate" which features the engraved legends, and a lower "mounting plate" to which all switches and other panel assemblies are mounted. The light plate is attached to the mount plate via No. 6-sized screws and nut-plates attached to the mounting plate. The finished light plate is to be 0.240±0.023 inch thick as per MIL-DTL-7788. The mounting plate is to be 0.064±0.003 inch thick as per MS25212.

Backlit panels within real-world aircraft in the US militaries come in several varieties as the years have gone on. Externally, all adhere to roughly the same physical specs, and internally, while the exact methods have ben changed refined over the years, all operate on the same working principle: Light is emitted within a transparent acrylic "light plate" which has been painted white and then black such that it has a white internal surface and black external surface. The light bounces and scatters off of the internal surface until it can escape through an engraving in the upper surface of the panel. The light plate connects electrically to the rest of the backlighting circuit via a plug connector on the bottom surface which seats in a receptacle mounted to the mount plate. The location of this connector is denoted on the top surface of the panel by an un-illuminated white cross or + symbol.

The lights contained within the light plate are generally placed away from engraved legends (ie, not directly below engraved areas). The quantity of embedded lamps is specified to be no more than 10, though it is evident that 12 were used for the ECS panel.

There are several types of backlit panels, the details of which are described in MIL-DTL-7788. Of note are Type IV, Type V, and Type VII panels.

Type IV - One piece integrally wired incandescent panels

These panels' light plates contain incandescent bulbs (MS90451 or MS90452) embedded within the panels. See the pictures section for an example of this type of light plate from a real F/A-18 ECS panel. The locations of the bulbs and the wire traces are depicted on the back in white paint. The backlighting circuit within the panel connects to a receptacle in the mounting plat via a MS90335-7 connector.

Type V - Printed circuit board panels

These panels have a recess in the rear surface of the panels for a removable circuit-board to which incandescent lamps (MS90451 or MR90452) are soldered. The circuit board is attached to the light plate via screws (No. 2 size) and the bottom surfaces of the plastic panel and circuit board should be flush. The electrical connection is made via an MS90335-8 connector.

Type VII - Light emitting diode (LED) panels

These panels are roughly the same as Type V panels, but the incandescent lamps are replaced with LEDs.

Proposed Alternative Backlighting Method ("Option B"):

The new backlighting method would utilize a construction similar to the real-life Type VII panel. The panel would consist of 3 layers: The light plate would be transparent acrylic which will have a recess milled out of its lower surface to accommodate the second layer, the backlighting PCB. Below this would be the mounting plate, analogous to the backplate from the existing backlighting option. The mounting plate could be any thickness from 1/16" (~1.6 mm) to 1/8" (~3 mm) and any material depending on the builder's preferences. 1/6" aluminum would the the most realistic option, while 3mm black acrylic would be a laser-cutter-friendly option.

Within the recess, pockets would need to be milled/routed to accept the LEDs. These pockets would need to remain unpainted to permit the light from the LEDs to enter the light plate. The rest of the panel would be first painted white to provide the inner white surface to reflect and scatter light throughout the panel, and then black. The appropriate legends would be engraved on the upper surface. Optionally, the engravings can be filled with translucent white epoxy paint (this is currently untested).

Fabricating a light plate would require three setups within a router and (optionally) laser cutter. The plate would be initially milled inverted such that the panel perimeter, recess, and any opaque pockets can be cut. The part can then be painted white and then black. The part would then be milled again in an inverted position to provide the un-painted pockets for the LEDs. Finally, the upper surface can be engraved, either in a laser engraver, or in the router with an engraving bit. The second and third setup will require proper indexing and positioning to the machine prior to the operation. Repeatability can be accomplished fairly easily in the router using re-usable 3d-printed jigs, and positioning within the laser cutter can be accomplished using the technique described by The Warthog Project in the Making Flight Sim Panels with my eBay Laser tutorial video.

Fabrication of the mounting plate would be accomplished either by CNC router or via laser cutter. Depending on the material chosen, this should present no additional challenges over those experienced with the existing option.

Electrical connection would be provided through the same connectors used in Option A, The connectors would protrude downward below the panel through holes in the mount plate.

Benefits:

This method adheres very similarly the how these panels are constructed in actual modern aircraft. The most notable exception to this is the fact that it appears un-necessary to directly attach the PCB to the light plate using small No 2 screws, and the fact that the electrical connection will be accomplished using Molex connectors rather than to a connector mounted to the mounting plate. This simplifies construction significantly, and also permits removal of the light plate and PCB without disassembly of the entire panel.

The mounting plate will now only require holes for mounted components (switches, buttons, standoffs, and panel sub-assemblies) and the PCB connector. Recesses for the LEDs will no longer be required within the mounting plate, increasing strength and rigidity. Mounting provisions for assemblies and standoffs can now be placed anywhere on the mounting plate without fear of interfering with the backlighting LEDs.

The number of LEDs required to illuminate the panel is also now substantially reduced. This reduces PCB cost and power requirements.

Disadvantages

The process required to fabricate an individual light plate is now substantially more complex, requiring several setups and increased time required for the manual painting step. The process also requires access to and working knowledge of a CNC router. Access to both a CNC router and laser engraver would be ideal.

Because the panel would be illuminated more broadly, there would no longer be the option to flash the backlight on individual legends on the panel. The option to flash an entire panel would remain through.

Alternative Fabrication options:

If routing a light-plate is not an option for the builder, and alternative construction method using 3 or 4 layers could be used to make an equivalent light plate using only through-cut operations. The viability of this method needs to be investigated.

Images and Video:

Real-life example

Below are images of a real light plate taken from the F/A-18's ECS panel.

CAD Images

Below are some CAD images that show the basic construction of the new panels.

Test ECS Light Plate

An attempt at a "replica" ECS light plate was made for testing and prototyping purposes using the method described. A positioning jig is shown being used to properly position the panel in the router for the second and third operations. The method is viable and shows good illumination characteristics when tested with a flashlight. The process does require refinement and optimization.

https://www.youtube.com/watch?v=OVwiUmxQqyk

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[L-Walker]

Very detailed breakdown. I'm a straight shooter and am just going to say, my boards are there, they are almost all done. The RWR and Defog lever are the only boards not yet with known working models. I've spent the cash getting them working.

If you do want to go the other route that is totally fine but either way I can no longer contribute in any way due to an increase in workload running my company.

Luke

On Mon, 15 Aug 2022 at 12:19, Erik Scott @.***> wrote:

Summary:

The existing backlighting method utilizes a multi-layer method that can be accomplished entirely using a laser cutter (and a manufactured PCB). While it provides good results, there are several issues associated with this design. A method more in-line with what is done on actual panels provides several significant benefits at the expense of slightly more difficult fabrication. Current Method ("Option A"): Overview:

The current backlighting method divides the panel into 4 layers. The top-most layer, referred to as the "legend plate" is a laser-engravable material consisting of a thin black upper surface and translucent white body. Panel legends and insignia are laser-engraved on the upper surface such that the white material is revealed. The second layer, referred to as the "light plate", is a translucent white acrylic layer used to diffuse light within the panel. The third layer is an opaque black acrylic layer, referred to as the "backplate", to which most switches, buttons and other panel components mount. Below that is the backlighting PCB, which contains connectors and a capacitor on its lower side, and addressable RGB SMD LEDs (red-green-blue, surface-mounted light-emitting diodes) on its upper surface. The LEDs are recessed in cutouts within the backplate. They shine up into the translucent light plate and the light ultimately escapes through the engravings in the upper surface of the legend plate, or is absorbed within the light plate or legend plate. The LEDs are positioned directly below the engraved labels, and are packed densely to provide even light distribution and avoid so-called "hot-spots" (distinctly bright areas) of the appearance of the backlighting. The individually addressable LEDs provide the ability to dim or brighten specific LEDs to further reduce hot-spots. Because of the number of LEDs and the relative density of the engraved areas on the legend plate on most panels, the number and size of the recesses required on the backplate become fairly extensive, resulting in a "swiss-cheesed" look of the backplate, which reduces the strength of this layer. This issue is largely mitigated by the strength provided by the other layers. The backplate must also be thick enough to accommodate the LEDs, usually necessitating 1/8" or 3mm thick acrylic. This is in addition to the thickness of the backlighting PCB, which is at least 1mm for reasonably-priced custom boards. The entire stack-up is held together with No. 6-32 screws. The edges of the legend plate and light plate must be manually painted black to prevent light-leakage. The light and legend plates can be optionally fused together to make a single panel similar to the light plates found in actual aircraft (see the real-life implementation section for details). Benefits:

This method was devised by @L-Walker https://github.com/L-Walker and has several benefits. Chief among these is the relative ease of construction, provided the builder has the appropriate materials and access to a laser cutter/engraver. The PCBs can be manufactured relatively cheaply from PCB manufacturing houses like JLCPCB with SMDs and connectors already soldered to the board. With each layer fabricated, the builder need only mount the switched to the backplate and backlighting PCBs and assemble the rest of the sandwich using No. 6 screws after painting the edges of the light and legend plates.

The individually addressable LEDs provide the ability to tune the brightness of specific LEDs to help eliminate hot-spots. Additionally the ability to flash the legends associated with a specific switch can help utilize the sim-pit as a training device, or help identify a switch during the setup phase. Disadvantages:

The necessity to use a 1/8" or 3mm backplate, plus the minimum 1mm backlighting PCB thickness results in a ~4mm thick panel for switches to mount to. The threaded bushing on many switches does not allow for this with sufficient thread engagement of the associated mounting nuts. Sometimes, even if sufficient thread does exist, the shafts of potentiometers, encoders, and rotary switches does not protrude high enough above the legend plate and into the associated knob to permit the set screws to grip the shaft. This limits the selection of switches available to use in the designs of panels and sometimes required the modification of knobs to re-position set-screws.

The requirement that the LEDs be recessed in the backplate requires that extensive amounts of the backplate be removed, resulting in the afore-mentioned "swiss cheesed look. This can potentially make the backplate relatively fragile and prone to breakage during assembly. Once assembled, however, this fragility is largely mitigated by the structure provided by the solid PCB from below and solid light and legend plates above.

The large amounts of space required by the LEDs, and the fact that the PCB is located below the light plate limits mounting options for switches, stand-offs, and more complex assemblies on the underside of the panel. Since screws cannot penetrate through areas located where LEDs are, and LEDs are located wherever legends are placed on the upper surface, mounting positions are very limited, especially on compact, non-standard panels such as the LDG GEAR panel.

Because the light-plate is translucent rather than transparent, light does not travel very far within the panel before being absorbed. This requires an extensive number of LEDs. This makes PCBs more expensive, presents potential power consumption issues, and exacerbates the issues presented above regarding backplate swiss-cheesing and mounting space. Real-life implementation: Overview:

The specs for real-world panels can be found in MS25212. In short, they consist of an upper plastic "light plate" which features the engraved legends, and a lower "mounting plate" to which all switches and other panel assemblies are mounted. The light plate is attached to the mount plate via No. 6-sized screws and nut-plates attached to the mounting plate. The finished light plate is to be 0.240±0.023 inch thick as per MIL-DTL-7788. The mounting plate is to be 0.064±0.003 inch thick as per MS25212.

Backlit panels within real-world aircraft in the US militaries come in several varieties as the years have gone on. Externally, all adhere to roughly the same physical specs, and internally, while the exact methods have ben changed refined over the years, all operate on the same working principle: Light is emitted within a transparent acrylic "light plate" which has been painted white and then black such that it has a white internal surface and black external surface. The light bounces and scatters off of the internal surface until it can escape through an engraving in the upper surface of the panel. The light plate connects electrically to the rest of the backlighting circuit via a plug connector on the bottom surface which seats in a receptacle mounted to the mount plate. The location of this connector is denoted on the top surface of the panel by an un-illuminated white cross or + symbol.

The lights contained within the light plate are generally placed away from engraved legends (ie, not directly below engraved areas). The quantity of embedded lamps is specified to be no more than 10, though it is evident that 12 were used for the ECS panel.

There are several types of backlit panels, the details of which are described in MIL-DTL-7788. Of note are Type IV, Type V, and Type VII panels. Type IV - One piece integrally wired incandescent panels

These panels' light plates contain incandescent bulbs (MS90451 or MS90452) embedded within the panels. See the pictures section for an example of this type of light plate from a real F/A-18 ECS panel. The locations of the bulbs and the wire traces are depicted on the back in white paint. The backlighting circuit within the panel connects to a receptacle in the mounting plat via a MS90335-7 connector. Type V - Printed circuit board panels

These panels have a recess in the rear surface of the panels for a removable circuit-board to which incandescent lamps (MS90451 or MR90452) are soldered. The circuit board is attached to the light plate via screws (No. 2 size) and the bottom surfaces of the plastic panel and circuit board should be flush. The electrical connection is made via an MS90335-8 connector. Type VII - Light emitting diode (LED) panels

These panels are roughly the same as Type V panels, but the incandescent lamps are replaced with LEDs. Proposed Alternative Backlighting Method ("Option B"):

The new backlighting method would utilize a construction similar to the real-life Type VII panel. The panel would consist of 3 layers: The light plate would be transparent acrylic which will have a recess milled out of its lower surface to accommodate the second layer, the backlighting PCB. Below this would be the mounting plate, analogous to the backplate from the existing backlighting option. The mounting plate could be any thickness from 1/16" (~1.6 mm) to 1/8" (~3 mm) and any material depending on the builder's preferences. 1/6" aluminum would the the most realistic option, while 3mm black acrylic would be a laser-cutter-friendly option.

Within the recess, pockets would need to be milled/routed to accept the LEDs. These pockets would need to remain unpainted to permit the light from the LEDs to enter the light plate. The rest of the panel would be first painted white to provide the inner white surface to reflect and scatter light throughout the panel, and then black. The appropriate legends would be engraved on the upper surface. Optionally, the engravings can be filled with translucent white epoxy paint (this is currently untested).

Fabricating a light plate would require three setups within a router and (optionally) laser cutter. The plate would be initially milled inverted such that the panel perimeter, recess, and any opaque pockets can be cut. The part can then be painted white and then black. The part would then be milled again in an inverted position to provide the un-painted pockets for the LEDs. Finally, the upper surface can be engraved, either in a laser engraver, or in the router with an engraving bit. The second and third setup will require proper indexing and positioning to the machine prior to the operation. Repeatability can be accomplished fairly easily in the router using re-usable 3d-printed jigs, and positioning within the laser cutter can be accomplished using the technique described by The Warthog Project in the Making Flight Sim Panels with my eBay Laser https://www.youtube.com/watch?v=GWwiDnhjQlo tutorial video.

Fabrication of the mounting plate would be accomplished either by CNC router or via laser cutter. Depending on the material chosen, this should present no additional challenges over those experienced with the existing option.

Electrical connection would be provided through the same connectors used in Option A, The connectors would protrude downward below the panel through holes in the mount plate. Benefits:

This method adheres very similarly the how these panels are constructed in actual modern aircraft. The most notable exception to this is the fact that it appears un-necessary to directly attach the PCB to the light plate using small No 2 screws, and the fact that the electrical connection will be accomplished using Molex connectors to a wire-lead rather than to a connector mounted to the mounting plate. This simplifies construction significantly, and also permits removal of the light plate and PCB without disassembly of the entire panel.

The mounting plate will now only require holes for mounted components (switches, buttons, standoffs, and panel sub-assemblies) and the PCB connector. Recesses for the LEDs will no longer be required within the mounting plate, increasing strength and rigidity. Mounting provisions for assemblies and standoffs can now be placed anywhere on the mounting plate without fear of interfering with the backlighting LEDs.

The number of LEDs required to illuminate the panel is also now substantially reduced. This reduces PCB cost and power requirements. Disadvantages

The process required to fabricate an individual light plate is now substantially more complex, requiring several setups and increased time required for the manual painting step. The process also requires access to and working knowledge of a CNC router. Access to both a CNC router and laser engraver would be ideal.

Because the panel would be illuminated more broadly, there would no longer be the option to flash the backlight on individual legends on the panel. The option to flash an entire panel would remain through. Alternative Fabrication options:

If routing a light-plate is not an option for the builder, and alternative construction method using 3 or 4 layers could be used to make an equivalent light plate using only through-cut operations. The viability of this method needs to be investigated. Images and Video: Real-life example

Below are images of a real light plate taken from the F/A-18's ECS panel. [image: PXL_20201201_023837196] https://user-images.githubusercontent.com/6752310/184566265-6773cc1d-92c2-475e-8f31-fca8caa26326.jpg [image: PXL_20201201_024136176] https://user-images.githubusercontent.com/6752310/184566263-81a51900-4fea-4337-889c-db8b09547ccc.jpg Test ECS Light Plate

An attempt at a "replica" ECS light plate was made for testing and prototyping purposes using the method described. A positioning jig is shown being used to properly position the panel in the router for the second and third operations. The method is viable and shows good illumination characteristics when tested with a flashlight. The process does require refinement and optimization. [image: PXL_20220702_230621116 MP] https://user-images.githubusercontent.com/6752310/184566540-e3cf6ecf-7a3d-4dea-93ba-ec932fe7aa0b.jpg [image: PXL_20220702_231411062] https://user-images.githubusercontent.com/6752310/184566549-c88a0551-afcd-48a3-a203-91813c305819.jpg [image: PXL_20220708_231247681] https://user-images.githubusercontent.com/6752310/184566558-dda0a36a-3b98-4338-8288-d8cb99eda910.jpg [image: PXL_20220716_220903951] https://user-images.githubusercontent.com/6752310/184566568-48999dc8-be36-4ca7-8138-3afaaa254ada.jpg [image: PXL_20220716_221204118] https://user-images.githubusercontent.com/6752310/184566577-e6cc0d4e-c9c0-4e29-b173-ef07bc0022d8.jpg [image: PXL_20220716_221843635] https://user-images.githubusercontent.com/6752310/184566584-010d1f2e-1853-492b-9949-f4b4791ec8c3.jpg

https://www.youtube.com/watch?v=OVwiUmxQqyk More Information

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[tekadept]

A short little pdf that describe a little on the process of real panels constructions I found in my travels https://www.primeproductsinc.com/wp-content/uploads/Illuminated_Components_Design_Guide-final.pdf