Custom BMA EFIS Lite Keypad: Updated 1-22-2006

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pad4.jpg (88500 bytes)Would you like to know how to make your own remote keypad for your Blue Mountain Avionics EFIS Lite?  Or, maybe you just want to put switches somewhere convenient and the remote keypad or buttons and knobs on the face aren't appealing.

First read this quote from the BMA installation manual and pilots guide; "NOTE: Do not use the bezel controls while the Programming Keyboard is plugged in. It may cause the bezel and/or keyboard to operate erratically."  This item IS plugged into the "programming keyboard" connection.  Therefore it is unwise to use the "DSP", " AP", "CKL" and "SET" keys or knobs on the face of the Lite while this is plugged in.  One of my suggestions for people that choose to make their own custom buttons would be to remove the knobs and flush-mount the Lite in a way that hides the buttons.

If you're ok with all that, your in luck!  I've put two and two together and come up with the most universal way to accomplish this.  You can basically put any EFIS Lite switch you want, anywhere in your plane that works for you.

I know that this works with my BMA EFIS Lite running version 2.20 software.  It may work with your Lite, but I haven't tested for that.

With these instructions you can make your own custom EFIS Lite remote key pad, or have push buttons on your stick, panel, overhead console, forehead, etc…

DSC00004.JPG (93422 bytes)First you will need a standard PS2 keyboard to donate to the cause.  I chose the Belkin Classic Keyboard, model number N10117, due to it's availability at Office Depot and the $11 price tag.

If you get lucky enough to get the Belkin N10117, you can use the pin-out on the chart below and your 90 percent done with the project.

If you can't find this keyboard, but you find any other standard PS2 keyboard, it's still easy to do.

DSC00005.JPG (92676 bytes)Whichever keyboard you choose, the first step is to verify that it works.  Plug it into your home computer and test it out.  Type a letter to your aunt for example.  She's probably waiting to hear from you.  Most importantly there are nine keys that you must ensure work properly.  Keys 1, 2, 3, 4, Up Arrow, Left Arrow, Right Arrow, Down Arrow and Enter.  To make this simple, stick to the individual arrow keys, the numbers above the letter keys and the enter key at the right of the letters.  Ignore the 10-key portion of the keyboard, this only complicates things.

Now that you've found a keyboard that works, it's time for some fun.  Turn the keyboard upside down on a clean work surface.  Remove all of the screws that hold the back of the keyboard on.

Carefully, lift the back of the keyboard away from the keys.  You should have in your hand a thin, possibly transparent, three layer PCB and after flipping the board over to be right side up, a small PCB in the upper right corner with three LEDs.

This small PCB is your ticket to design freedom.  The only thing you have to figure out is which two wires are connected when each of the nine keys are pressed.  I used a simple, visual, mapping method.  You could also use a multi-meter.  Be sure to remove the controller from the board before using your meter.

My method went like this;  I labeled the upper and lower, transparent PCB at each of the nine key locations.  Then, I placed a piece of white paper between the layers to make the traces easier to follow.  Next, I labeled the pins on the controller 1-26 from left to right with the controller board situated so that I could read the printing on it.  Finally, I followed each of the traces on the transparent PCB to the controller connector and built the chart below with the pin numbers for each key.

Keyboard: EFIS Lite Keypad Button/knob:

Belkin #N10117 PS2 Controller Pin numbers:

1 DSP 26 1
2 AP 26 2
3 CKL 26 3
4 SET 26 4
Left Arrow Outer Knob Left 24 8
Right Arrow Outer Knob Right 24 10
Up Arrow Inner Knob Left 22 8
Down Arrow Inner Knob Right 24 11
Enter Inner Knob Push 23 13

pad2.jpg (93917 bytes)I came up with a total of 12 pins that will be used on the controller.  If you are reading this,  you have probably already decided where you want your switches to be mounted.  All that is left now is to wire the controller to the switches according to the mapping that you just discovered.  

Soldering 22 awg wire to the controller board is an easy way to accomplish this.  I drilled tiny holes into the control board to stick the wires through and then soldered them to the bare copper on the board.  Make sure you hot-glue or epoxy the wires to the controller board for strain relief. 

pad3.jpg (93724 bytes)For the 1-4 and Enter keys, I was going to use small, momentary push-button switches.  For the arrow keys, I was going to use two miniature DPDT (on)-off-(on) momentary toggle switches.  The least confusing way to do this would be to mount the toggles so one operates left-right and the other operates up-down.  From a human factors stand-point, it's hard to beat the knobs, but this comes close.

I decided to change the toggle switches and push buttons to a pair of 4-way hat switches with a momentary toggle between them for the "enter" button.  I placed the two hat switches vertical and the toggle is spring load when pushed to the right to activate.  The upper hat switch is up for the "CKL" command, right for the "DSP" command, left for the "SET" command and down for the "AP" command.  The lower hat switch replaces the knobs with up for the "up-arrow" command, right for the "rigth-arrow" command, left for the "left-arrow" command and down for the "down-arrow" command (see chart above for comparison to knobs).

Update 1-22-2006:

pad1.jpg (84303 bytes)The PS2 connector is already properly wired for your programming keyboard port on your EFIS Lite system.  To the left is a pin-out of the Mini Din keyboard connector.  I put the entire assembly inside of a small project box that will mount behind the instrument panel.  The toggle switch cover and the small screw below the lower hat switch will hold the assembly to the panel with the hat switches poking through .8" diameter holes.

After assembly I verified proper operation by connecting it to my laptop keyboard port.pad5.jpg (30128 bytes)HatSwitches.jpg (82674 bytes)

Finally a shot of the switch assembly mounted in the center panel.  With this design my hand rests on the throttle with my elbow on the center console. I can reach all critical switches without moving my hand more than an inch or so from this area. (note: you gotta love the temporary labels. :-)

As usual, feedback is welcome.

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