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Keytronics Keyboard Hex Keypad Conversion

Strictly speaking, this isn't an Apple-1 article as much as it is an article about modifying a Keytronics keyboard. (It appears in this exhibit because the Apple-1 happens to be the only system in this collection that utilizes a Keytronics ASCII parallel keyboard.)

That said, unless you plan to use your Apple-1 as an adding machine, aren't the extra keys around the numeric keypad of a Keytronics keyboard kind of useless? Since the Apple-1 is designed to be programmed directly in hexadecimal anyway, wouldn't a nice hex keypad be handy as well as functional? Well, here's one way you can perform that conversion on your Keytronics keyboard, turning those wasted calculator keys into a useful hex keypad.

Of course you could always simply cut all traces to all 6 keys we want to turn into hex characters and splice them directly with 12 wires over to the appropriate letter key pads on the keyboard. Unfortunately cutting some of the traces will also have the effect of cutting other keys off from cross-board runs, so those cuts would have to be bypassed with additional wires - a process that gets ugly pretty fast. However, with a strategic selection of which letters we assign to which keys, and a little reuse of the existing traces, the same task can be accomplished by cutting fewer traces, and running considerably fewer (and shorter) wires.

To make soldering as easy as possible, rather than attempting to attach any wires directly to board traces using surface soldering, all wires are run instead from existing thru-holes on the board, and where it is necessary to solder to the keypad a small hole is drilled, and the wire brought up to the pad from the back of the board. To drill the actual holes I used a hand drill with a very small bit, as illustrated in the pictures and video in the gallery. Note that in a few cases the pad partially overlaps a trace running underneath on the other side of the board, so be sure to hold the board up to a light and make sure from both directions that your hole is located such that you are not going to accidentally drill through an underlying trace. Also note that drill bits of this size are very fragile and will break easily. (I broke mine about 4 holes into my second keyboard, as shown in the image gallery.)

The most effective approach I found for placing wires in the pre-existing thru holes was to strip about 1/4 inch of insulation, open the hole with the soldering iron and push the wire through just to where the insulation is flush with the board (be careful not to push too far and get the insulation into the solder), then remove heat, bend the wire 90 degrees, and tape the wire down. Then flip the board over, "clean up" the connection by properly heating the wire and board and applying a little fresh solder, then snip off the protruding wire.

Soldering to the keypads is similar, except no initial application of heat is required to put the wires through the holes (as they are freshly drilled.) Once the wire is through and taped, the board can be flipped, the wire bent over by pushing at the bottom with a small screwdriver, and it will stay secure long enough to solder it to the pad, being careful to keep the solder as far away from the center of the pad as possible, and the whole joint as flat as possible, to avoid the solder interfering with the proper operation of the key. (Use the minimum amount of solder necessary to get a good connection!) Note that it is also very important to clean up the solder connections with contact cleaner before reassembly, as the flux from the solder can act as both an insulator and as a glue to adhere to the silver pads on the keys. (The only key that gets drilled in this design besides the 6 keys that are being converted to hex keys is the number pad 8, so you are not compromising the functionality of any of the main keys, in any case.)

Once you have completed the wiring and reassembled the keyboard, you are ready to apply labels to the keys to indicate their new functions. Model railroaders wet transfer decals make a good choice for this, as long as you are very careful to insure that no drops of water remain on the label to run down the key and into the keyboard. The alternative, although not quite "period", is to use transparent laser printer labels.

The Library Documents section at the bottom of this article contains links to two PDF documents, one showing the actual cuts and jumpers that need to be installed, and the other illustrating schematically how the changes actually work based on the key matrix. There are photographs of the entire process from end to end, and even a couple (poorly filmed and completely unedited) videos to assist you should you attempt to undertake this project on your own Keytronics keyboard. Lastly is an actual action shot of the hex keypad in use, keying in the entire test program from the Apple-1 manual using the pad.

PLEASE NOTE: Like all DIY exhibits on this site, the information contained herein is strictly for educational/entertainment purposes, no warranty is offered nor is the information within guaranteed to be suitable for yours or any other use. (In other words folks, it worked for me, but do it yourself at your own risk, because I won't be able to help you if you break your keyboard. I actually have three, so that made me quite a bit braver than I might have been to do the first one if I only had one keyboard. They aren't easy to find these days.)

You will note in one of the pre-disassembly pictures an anti-static strap, and you will also note that I left the anti-static tape under the decoder at all times while I was working on the keyboard, to minimize the chance of taking out the delicate 20+ year old electronics with a stray static charge. Apparently it was enough, because I have converted two now without any problems.

Enjoy!

Image Gallery
NOTE: Images beginning with 100 and up are larger versions of the same numbered lower resolution images +100. Not all images appear in high resolution format.

000 Front View (jpg, 63 KB)	001 Keyboard Top View (jpg, 165 KB)	002 Bottom View (jpg, 181 KB)	003 Bottom View Static Protection Removed (jpg, 184 KB)	004 Bottom View Angle (jpg, 168 KB)
005 Disassambled View (jpg, 210 KB)	006 Top View Open (jpg, 111 KB)	007 Tools for the job (jpg, 166 KB)	008 VIDEO Cutting the traces (asf, 1.9 MB)	009 VIDEO Drilling the holes (asf, 3.9 MB)
010 First Hole Drilled (jpg, 147 KB)	011 All Holes Drilled (jpg, 152 KB)	012 Soldering tools (jpg, 185 KB)	013 VIDEO Soldering to the pads (asf, 4.1 MB)	014 First pad soldered (jpg, 187 KB)
015 All pads soldered (jpg, 237 KB)	016 Completed wiring top (jpg, 409 KB)	017 Completed wiring bottom (jpg, 174 KB)	018 Bottom View Angle (jpg, 161 KB)	019 Labels applied (jpg, 253 KB)
020 Installed View 1 (jpg, 212 KB)	021 Installed View 2 (jpg, 218 KB)	102 Bottom View LG (jpg, 2.1 MB)	103 Bottom View Static Protection Removed LG (jpg, 2.1 MB)	105 Disassambled View LG (jpg, 2.3 MB)
106 Top View Open LG (jpg, 1.2 MB)	110 First Hole Drilled LG (jpg, 315 KB)	111 All Holes Drilled LG (jpg, 424 KB)	117 Completed wiring bottom LG (jpg, 1.3 MB)	120 Installed View 1 LG (jpg, 2.3 MB)
121 Installed View 2 LG (jpg, 2.3 MB)	122 VIDEO using the keypad (asf, 13.4 MB)