That's an interesting thought, and would allow the whole thing to act like a USB keyboard as well.
That could also mean changing the layout on the fly, without having to re-wire the whole thing.

The hard part would be using the arduino to act like a keypad, such that the calculator thinks it is hooked up to physical switches when it is really only hooked up to an arduino.
There are some really good programmers on this site, so it may be possible. Probably using interrupts.
But that would mean needing 7 or 8 interrupt pins on the mcu... could be possible...

A bit of a bump, I have been working on some things.

I ordered a 39-pin 0.3mm pitch FFC extension cable, direct from China, so it will be delivered at the end of the month or even January.

The design for the case and PCB are coming along well, but I still need to so a bit more research and testing. Here are some preliminary renders:





I still need to purchase a new CE to take measurements of the calculator PCB and screen, and design parts to hold them in place.

The PCB has hole, pads, and wiring to support single-color LED's on each of they keys, along with the SMD resistors to match. I have not designed a keyboard PCB before, but have designed PCB's for other projects, so it wasn't too bad. I used Eagle and its auto-router, and set very generous DRC guidelines, so it should be pretty easy for any PCB fab-house to make.

Having LED's on would definitely drain the the calculator's battery pretty quick, so I am thinking of putting a separate battery for those? or a compartment for AAA's? Or just a larger battery to run the whole thing? Let me know what you think about the LED power consumption and battery.

The top plate I will most likely have laser-cut from clear acrylic, as that is what my university's makerspace has for 1/16" or 1.5mm stock. The bottom case will most likely be 3D-printed in 2 halves, which is what will fit on my printer.
(I am looking for a justified reason to buy a bigger/better printer, and this may be it!)

This project is coming along pretty well, and I am ordering more parts, particularly the PCB, as soon as I can get a CE to check my designs and spacings.



To order PCB's, plates, keycaps, and other parts, bulk orders are cheaper than one-offs. To make this project affordable, it would be great if there were more than just one made.
Would any of you be interested in purchasing one of these? It would have to be a kit, as I can't supply the calculators or the key switches. And a rough guess for price would be about $150 $80 plus shipping, but I would have to tally that up a bit more accurately when I have the designs finished.
Anyone interested?

I think I would definitely want to purchase a kit like this. $80 seems like a reasonable price. Plus, those renders look awesome!
I think with the battery, both a separate lipo and a bigger batter (with the same voltage output) would work, so long as they can both be charged via one usb port. Speaking of usb port, where are you thinking of putting it? I think that near the top left/right, like a keyboard, would work well.
(FYI, I have a lulzbot taz 6 and could print prototypes for ya. Let me know if I could be of assistance.)

Keep up the amazing work!
-Knights

I know I've said it in IRC, but I'm definitely interested, possibly in two sets.

In terms of battery, one option is to just tap into the CE's normal battery. LEDs would definitely reduce battery life, but possibly not by that much. It's a desk calculator, so could presumably stand to stay on USB power almost all the time.

For longer runtime, it should be possible to connect a standard cell like a 16550 in place of the CE's normal battery and use the CE's normal charge circuit. (ofc make sure the battery is the same chemistry, and have fuses, etc.)

Why not laser-cut the whole case (in several layers)? If you make it out of relatively thick material, it should be possible to drill holes so screw or bolt heads are recessed (or other options, like using rubber feet to cover heads). Depending on how easy printing is, though (I've had bad luck with large flat things lift off the bed) printing could be easier.

What are you thinking in terms of keycaps? I've seen keyboards that have laser-engraved legends on light-colored plastics. You could engrave many at once (eg a full set) with an appropriate jig for alignment. Make sure the plastic is compatible with laser engravers - I know some plastics produce toxic/corrosive fumes when cut.

You bring up some really good points.

Tapping into the CE's battery is probably the way to go, or getting a larger flat lithium polymer cell in it's place. It is a desk calculator, so being plugged in probably won't be an issue, and the stock battery will handle just fine, as there is no added load when the LEDs are off.

The move towards a printed case and only lazer cutting the top plate is a financial one. To cut that many prices of acrylic, or any material, on a laser that I do not own, is expensive. The price for laser cutting is a combination of number of sheets used, and the time it takes to cut it. So less pieces would be a lot more affordable.
I have access to a 3d printer that would be much cheaper than using the laser, and require less finagling to assemble as a kit. Large flat prints turn out alright when using a flexible base on the printer.

For the keycaps, I am thinking of doing some diy dye sublimation on blank PBT keycaps. It would take some time, but would be a fun task to do while watching a movie or something. Doing it myself would be the most cost effective way, want to keep this as cheap for myself (and for you all) as possible. If I am going to make more than 5 of these, then I would contact a company like Signature Plastics or GMK for a production run, probably laser etched ABS. I don't have access to a laser engraver (my University only allows the laser to be used for cutting), so diy dye sublimation is the best bet so far. I can order printed dye-sub transfer paper sheets on Etsy for like $4 per board.

I'll keep this thread updated, and post an interest poll to see what kind of price point people are willing to buy a kit.

Progress Update here:

I have purchased a rev. N calculator, with the help of jacobly and others on SAX/IRC/Discord to ensure I was getting at least a rev. M. I was extremely lucky to buy the rev. N that ran OS version 5.4.0, and while not a great as 5.3.0, at least still supports ASM without needing arTIfiCE, so YAY!

Here are some pictures of the packaging:




I took it home and disassembled it, ripped out the PCB and screen to do some reverse-engineering and getting measurements for CAD and case design.
I photocopied both sides of the PCB to take notes as I go around with a multimeter:




Tracing all of the buttons and test pads, I have come up with this layout, which pretty closely matches the register data table used when reading keypresses on with assembly.
The ON button is the only exception, where there are 3 contacts instead of 2, 1 of which is ground. shorting ON1 and ON2 presses the on button, and so does shorting ON1 and ground, but I am thinking shorting ON1 and ON2 would be the best bet.
Here is this layout:



I have modeled the PCB and screen, and am currently working on the bezel and case design that fits tightly, but with enough room for wiring.
I am also debating 3d printing the whole thing. May be a bit cheaper feeling, but iterating the design would be much more affordable. Having the PCB in place would keep it relatively stiff.
I may also have the opportunity to have the plate laser-cut out of stainless steel.
If any of you have access to a laser cutter, or know of some in the south-east US, let me know.

As per the poll, it is apparent that keeping the total cost under $40 would result in the most interest.
There is not much cost to cut on the PCB and keycaps, so the Case is where the budget has to go.

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Some more work on the PCB, incorporating some of my findings about the ON button needing separate wires:


I have ordered 5 of these PCB's from JLCPCB, and also paid for them to put 470ohm SMD resistors for each LED, so no tedious surface-mount soldering needed.

When I get back from vacation this weekend, I will order keycaps and try out some dye-sub techniques.

Yeah, there is a board known as a Teensy, it has an incredibly fast processor for such a small board, and as I can remember, every single pin on it can be used as an interrupt pin. It is compatible with the Arduino IDE with a bit of tinkering. This might be a bit of a stretch, but you might be able to create some kind of serial interface that allows the calculator to take advantage of the processor.

EDIT: Here's a link https://www.pjrc.com/store/teensy40.html

Oh yeah, the teensy would fit the bill nicely! It has enough interrupt pins to piggy-back off of the calculator scanning the key matrix, at it can act like a USB HID keyboard.

That would definitely be an interesting feature to add, but perhaps a bit better but of the price range for this project. But yes, very possible. There will be enough room in the case to for a teensy, so if anyone buying a kit wants to pursue that avenue, there option is there.

-----------------

I wrote a short program (<1500B) that tests they keyswitches, and displays which ones are/have been pressed. Here is a gif:

It has options for the normal calculator layout, as well as the layout for the TI-84 KE.
I will upload to the archives and link it here shortly. Here is the KEYTESTR Program
This will allow for quick testing when building the kit.

Over the weekend, I have been working on designing legends for the keycaps. I have found a font that is close to the font used on the CE keypad itself.
I have also purchased enough blank DSA profile PBT keycaps in different colors (white, light grey, green, and blue) to make 5 keycap sets. The keycaps are most likely going to be the most expensive part of the kit.

I have also ordered 5 PCB's, and am consulting with a handful of laser cutting services to make the plate, probably out of stainless steel.

Here is a snippet of the keycap legends so far:


I have found an Etsy page to buy dye-sub prints, so I will email a PDF of the keycap legends to them and do the dye-sub myself. There was a plan to have tr1p1ea do the dye-sub, but unfortunately, his press does not work like he thought it did. No worries!


In response to the poll, the target price will be $50+s/h. For this first run, I am only making 5 kits, one for myself and 4 to sell.

If you would like to buy one, please PM me here or on Discord. There are already a few reservations, so if the demand is large enough, I can make 5 more, for a total of 9 to be sold.

I have been working more on the keycap legends, and have come up with this design:



The goal is to be pretty faithful to the legends on the 84, with the exceptions of "stat plot", "format", "catalog" and "solve". These words were just too long.

I have enough keycaps ordered to make a few novelty keys, one in each color, for each kit. In the image above, they are:
The "=" key, falls in line with the +-*/ keys.
The "terminal" icon, in place of the "prgm" key.
A Cemetech Icon (green is just a placeholder, I suppose it could go anywhere)
A Texas Instruments Icon (again, white is just a placeholder)

I have a few questions for feedback:

1) Would there be a trademark/copyright issue with me making TI logo keycaps and selling them?
2) Would Kerm and other Cemetech staff be okay with me making and selling/shipping Cemetech keycaps?
3) What do you think about the font and style of legends? About the "2nd" and "alpha" legend placement?
4) What other ideas do you have for novelty keys? Like the on/off key, different ideas for the backlight key? I'd love to hear your thoughts and get suggestions.

That's looking pretty good! The fonts look pretty much like the real thing! I assume you're using Helvetica CE 55 Roman? Cutting a few long words short looks ok to me, not even TI could fit such long words within a single button space!

I spotted just a few errors in the current legend. The [x⁻²] key (second row from the top, 5 columns from the right) should be [x²]. The other is the [.] key is missing the blue i. There's one improvement on the TI-84 Plus CE-t Python Edition that's not on a regular TI-84 Plus CE, but I think would be nice to have. Pressing [alpha]>[XT0n] brings up a mathprint fraction, you can see it it's notated in this image: https://tiplanet.org/forum/gallery/image_page.php?album_id=632&image_id=12711

Personally, I think it'd be neat to have the Cemetech logo as the backlight key. I have no idea if you'll run into legal issues with a TI logo even with a project as small scale as this, but I think a Cemetech logo would look cooler regardless. If possible, could you show a Cemetech key with the C more bold? I'd just like to see how it looks compared to the current one.

This project is coming along nicely, great work!

Good guess, but I cannot find Helvetica CE 55 Roman in Inkscape (nor do I know how to add different fonts). I am using, for the most part, Nirmala UI.

I don't want to get in trouble with TI either, or cause any more drama between TI and the community. I agree that having the Cemetech logo as the backlight key would be pretty cool. Here are some options for boldness of the logo:


Love the addition of the mathprint fraction key, I think it fits nicely with the keycap set. It is in the render as well.
My best attempt at that stylized "i" is there as well, what do you think?

Thank you for the support, I hope this project turns out nicely. The keycaps I ordered from AliExpress, so... that may be the last thing to arrive at my door, maybe even over 2 months wait.

It has been a little while since I've looked at this topic. Looking through the things I've missed, I am very impressed. I think that this project is absolutely amazing and I can't wait for it to be completed!
I think that the keys (from the above post) look great. I really like the addition of the Cemetech logo on the backlight key. Keep up the hard work NoahK.

Thank you all for your support so far! This is a bit of a wall, so here is a tl:dr,
Claim a kit if you want one, <=$70, Metal plate need laser fab, Need custom keycap ideas, Need software ideas, permission to use Cemetech logo.

----------------------

I have updated the to-do list on the top post, so it is time for an update here.
There are already 2 (?) of the kits claimed: TheLastMillennial and matkeller19. I also have tentative claims for Kerm, Hooloovoo, BioHazard, and TIny_Hacker. If you are any of these people, or want to be added to this list, please PM me here or on Discord, so we can work out details.

The price will be at most $70 plus shipping. Turns out it is not cheap to get parts fabricated.

The last couple of thing to figure out for this project are the Plate, and the Case.
After chatting on SAX, it has been determined that a metal laser-cut plate would be the best option.
I am talking with a laser cutting company local to me, and have found a good deal on sendcutsend.com.
It would either be stainless steel or aluminum, I am thinking stainless steel.
If any of you have or have connections with someone who has a laser cutter, please let me know.

The case will be simpler to 3D print, due to its size and the need to change the design a little, I'm not the best at CAD the first-go-around. I have access to a large 3D printer through my university that can print the cases.

I have ordered blank keycaps, PCB's, screen ribbon cable extenders, and some other nuts and bolts. Delivery time from China for the keycaps and ribbon cables is in the range of weeks up to 2 months, so this project will have a lot of down time.

I will have some spare keycaps, and have discussed 2 posts prior about some custom legends, like the Cemetech logo (with Kerm's permission (do I have your permission?) (I already silkscreened "cemetech.net" on the PCBs, sorry)), alternate enter key, or alternate 2nd and Alpha keys. What other alternate keycap ideas do you have?

The other part of the plan, and something to do in the downtime, is to have a little suite of software for the CE that can take advantage of the keyboard-esque layout. I am learning C for the CE, and have already ported that keypad tester program to C.
What are some ideas that you have for software for this thing? What would you like to see?

Small update:

PCB's came in! I have continuity-tested (beeped-out) one of them, and it seems good.
I have ordered and/or received every single part to ship out kits except for the 3d prints I need to do for the case. So, everything is ordered, just waiting for delivery (yay postal service 2020)
The mounting plate will be stainless steel. The decision was made on IRC/SAX about a week ago.

Currently, I have 3-4 kits that people have claimed. There are only 4 kits available. There are more people that have said they were interested.

This first batch, as promised, will be $70 per kit, plus shipping. With the time and small-batch-ed-ness of it, I am selling these at a loss, but that is okay. If there is enough demand, I would love to do another batch of 5 or 10 more kits, with some minor upgrades and compatibility with monochrome calcs, but would have to sell them at a higher price, probably $90. If you think I should do another batch, let me know.

I will add pics and run a poll when I get back from family's next week. I am also moving to a new apartment after Christmas, so updates here will be a bit slow until January.

As promised, here is a wall of pictures and some annotations to dress it up as a build log:
Click any of the photos to see a full-res version

Firstly, the PCB's came in last week!
JLCPCB had them done cheap and fast, and actually pretty good quality.
I continuity-tested the pads on one of them, and it all works out.
I had them place and solder the little 0805 SMD 470ohm resistors.
This means no SMD soldering needed to assemble the kits (yay!).




Secondly, and maybe even more excitingly, the laser cut stainless steel mounting plates came in!
Here they are straight out the packaging from SendCutSend.
Based in Nevada (Made in USA), they are actually the most affordable place I could find.




Checking with my calipers, the cutouts came out just the right size at 14mm.
The plate was .060 inches thick, which falls within the 1.4-1.6mm spec of Cherry switch plates.
The 3mm holes for the bolts measured at 2.7mm, so I will have to drill those out to 3mm.




I tried fitting some M3 bolts through the holes, but they did not go through. 2.7mm is too small.
Fitting a few Cherry-MX-compatible switches was flawless. They snapped into the plate perfectly.
The switches' plate retaining clips are snug against the plate. (My switch is the Hako Violet)




After seeing that switch fit, I kitted the whole plate out with switches.
Each switch fit snugly and snapped right into place.
The switches I am using are plate-mount (3-pin), so it makes sense to snap all switches into plate before soldering to PCB.
If the switches were 5-pin (PCB-mount), it would make sense to pop just a few into the plate first.
Once you solder those, then snap the rest of the switches into the plate and PCB at the same time.
For this case design, the plate is integral to the case, so going plate-less is not an option.




I am glad to see that the PCB holes line up perfectly with the switches installed in the plate.
Here are a few more beauty shots, and a size comparison to an un-modified TI-84 CE.
The white plastic screen bezel near the end of pictures is a prototype, that part will get its own post.





And lastly, here is a demonstration of the longest calculator screen extension cable that I have ever seen:




This project is coming a long way. Just a few more things to polish up before they are shipped!
The final parts still in shipment are the rest of the screen extension cables and the keycaps.
Then comes the tedious process of printing legends on all of the keycaps. That will be fun!

I will attempt to make a comprehensive and easy-to-follow build guide / assembly instruction pdf & video.
That should help the people who are buying these kits assemble it without too much difficulty.
So, I am taking as many photos as I can during my own assembly process.

I am pretty busy through the rest of the year, so more updates will come as I work on this into Jan/Feb.

Looks amazing!

This is some awesome work, it's cool to see it start come together!

*Bump*
Any news lately?

Thanks for the bump TheLastMillennial. There has been a lot of news lately! Just finding the time to make a post here, and it's going to be a big one.

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THE 3D PRINTING AND KEYCAPS UPDATE

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Since the turn of the new year, and the whole month of January, a lot has happened on the TI-84 KE project.
Parts have been coming in slowly, and progress is being made. It is starting to look pretty good!
I purchased a new 3D printer to make the cases for the keyboard. The Creality CR10S Pro V2.
300x300x400mm build volume, so large enough to make keyboard cases, model airplane parts, and everything in-between.

Starting out with the calculator motherboard and backlight power switch circuit mounting positions, I printed out test pieces to make sure everything would fit:

Finding a spot to put a reset switch, it took a few test prints to find the perfect fit:

It took a few tries, but the battery compartment is re-created, so the donor calculator's battery cover is reused in the new case.
This allows the original battery to be used, and retains the functionality of the removable battery without increasing the enclosure's thickness:

Combined with the prototype screen bezel, here is the total thickness:


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In addition, the keycaps came in from overseas! They are the right colors, and the right quantity. Here are 5 sets in bags, one laid out:

And here are they blank keycaps on the switches/plate itself. The number keys are from a standard keyboard numpad:

They blank keycaps are PBT material DSA profile, ordered from AliExpress. The color is consistent, the only downside is the blue is slightly darker than expected.

But, you say, blank keycaps would be nightmare on a calculator! The solution: Printing legends using dye sublimation.
With help from you all on chat, I designed key legends for all 51 keys. The legends include the 2nd and Alpha functions.
I ordered dye sublimation prints of the legends from a shop on Etsy, and they arrived at my door in a few days. The navy ended up a bit more purple than blue .

Heading down to the dollar store, I picked up a cheap hair straightener and a spring clamp. To apply legends to the caps, heat and pressure is applied.
Each legend has to be lined up on the key, held in place with some tape, and then clamped against the key while in the iron for 2 minutes. Here is my setup:

A few layers of cuts from a silicone baking sheet provide padding and even pressure across the whole key. Here are the first row of keys while I perfected the technique:

That first row took me over an hour, and it wasn't that consistent. Finally getting into a grove, and tuning in the heat and timer settings, here is the full set! (3hrs):


So, keycaps can be printed, and the case has come along nicely. I printed a full-size case in black (by chat poll). Putting it all together, here are the current photos:




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Major tasks left to do before selling/shipping:
- Solder all electronics together and test everything works
- Re-design the screen bezel for a better fit and easier installation
- Dye-dub the other 4 sets of keycaps (will take about 20 hours)
- Write an instruction booklet/video instructions for assembly of the kit

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This project is the largest and most "professional" project that I have ever taken on, and the journey continues to be fun and fulfilling.
I will keep you all updated. Thank you for the encouragement and patience.

This is an amazing update!

The key process although tedious, has yielded fantastic results. I also like the idea of including the donor calc battery door.

Can't wait to see the finished product!