Great news everyone! I've fixed the USB port and completed the project!

Second Battery Updates:
Not a whole lot here has changed, the main difference is I've used Kapton tape to isolate it from the PCB and I've covered the battery contacts in tape. I've also secured it to the PCB so it doesn't jiggle around at all.

Wireless Charging Updates:
I've basically redone everything on the inside and did it right this time. I received a wide variety of soldering iron tips which made soldering in such tight places much easier! Who knew that the right tools would make a job much better?

First, I de-soldered the wires from the USB port and cleaned up the connections. I made certain there were no shorts in the port then I plugged it into my computer. Voila! I've never been happier to see TI Connect CE bring up my calculator's contents! I immediately backed up all the files on the calculator and ran a USB self test which it passed with flying colors!

(As usual, click for full size)

I'm still unsure why the USB port didn't work even if unconnected wires were on it, but I'm just glad it's fixed now. I then soldered the wireless charging leads to the charging station contacts at the bottom of the calculator which I should have done in the first place! Finally, I wrapped everything up in Kapton tape and I closed up the calculator. Fortunately, it works even better than new! The wireless charger works, so does the second battery, and the USB port is fixed.



There is something a bit odd with the wireless charger. For some reason when I put it on my new charging pad it makes the pad emit noises like chirping or sometimes a tone. It's not very high pitched which is what confuses me. It doesn't make any noise at all when I put just my iPhone on it. My best guess is maybe the receiver inside the calculator is too far away since the charging pad didn't emit noise when I was testing the receiver outside the shell. The only negative effect I've noticed is the charging pad and the shell of the calculator are warm where the coils are. The temperatures aren't even close to alarming though.

Backlighting Keys Update:
I think I'm going to hold off on this one for now. It appears that I just can't find small LEDs out there that are bright enough without drawing a ton of amperage. Even if the batteries can handle the load, I'm not sure I'm comfortable with how much they heated up during my tests. That's not to say I'll never come back to this again, I'll just have to look deeper, or get a 3D Printer to create thinner keys (which is more likely to happen).

Conclusion:
Unless there's something drastically wrong with with what I've done, I'm going to call this project complete. Would I recommend doing any of these mods yourself? I'd say no to double batteries due to the risk of something going drastically wrong. However, the wireless charging mod actually isn't dangerous if you do it the right way. All you need to do is cut away the shell to make room for it, secure it to the back shell, and solder the leads to the charging station contacts which hardly anyone here uses anyways. I may even do it to my own revision M CE. I had a lot of fun with this project, even if I got scared to death last post. I'm looking forward to trying more modifications in the future!

I have considered adding built in recharging into Casio Prizms (FX-CG10/20/50) but was not sure how to do it - the calculator has 4 removable AAA batteries and supposed to work on both alkaline and Ni-MH baateries (changable in the settings) and it has a mini usb port for data transfer with the calculator acting as slave device but does not charge batteries as far as I can see - what would be necessary steps and parts to make the Ni-MH batteries charge in the the calculator when it is connected to a usb power source via existing USB port on the calculator please?

I'd suggest creating a new topic amazonka, it's quite an interesting project!

I do forsee a lot of issues though

• I highly discourage soldering anything directly to the USB port, it can cause data transfer to fail.
  
• Even if soldering to the USB port works, you'll probably need to find a way to disconnect the calculator from USB power while charging the batteries.
  
• Rechargeable battery chargers have a lot of bulky components inside. I don't know how much space is free inside the Prizm but you could easily run into clearance issues.
  
• The batteries are probably hooked up all in series so you'll need to connect each battery to the charger separately and potentially find a way to disconnect each battery from each other while charging.
  
• I doubt you'll be able to use the calculator while charging which is probably the whole point of this project.

I'm not sure it's worth the trouble to try and get AAA charging implemented. Perhaps you can find a Li-ion battery of the correct voltage and implement a small BMIC. I don't know where you'd connect the charger if not on the original USB port though.

As I've proven in this thread, I'm no hardware expert so don't let this shoot down your idea. Just be sure you're thinking of potential issues and be sure you can find a way around them! Good luck!

All good points, thank you. I will resurect a post where I first planned to have this as part of a slightly bigger project - https://www.cemetech.net/forum/viewtopic.php?t=11814 and share your insights. Thanks again

All right, for those who wanted to try adding wireless charging to your calculator, I've made a tutorial! It's not difficult if you're familiar with soldering but I offered alternatives if you've never soldered or if you don't have certain equipment like a multi meter.

Nice job on the project and the video, TheLastMillennial! Those final clips of putting the calculator down on a charging pad and the charging LED lighting up are pretty impressive, and I don't have any major criticisms of how you did it (maybe a minor nit of passing the amount of current used for charging through magnet wire). Keep up the good work.

Thank you for this detailed tutorial - any idea why charging stations would no longer work with the mod please?

Thank you Kerm! I had quite a fun time with this project!

Amazonka: when I first tried to connect the wireless receiver I connected it to the USB port which caused major issues when I tried to use it for data communication. Although the charging contacts have no data communication abilities, I highly doubt that forcing current through the receiver is any good for it.

I never measured exactly how much current was going through the receiver that shouldn't have, so it may have not been very much. However, I decided to take precautions and disable charging stations than risk components breaking.

Just pop on a diode or two and you'll be fine.

Thank you both for your answers - so are diodes needed for sure please? And if so which ones shall I get please (considering the voltage drop may be an issue presumably)? I also conteplated bulding in the recever into the cover enabling wireless charging only while the cover is on the back but it appears the contacts on the cover will be an obstraction for putting the cover on the front ;-(

A few days ago, I took apart an old Bluetooth speaker (it's a Jellybox by OrigAudio) that didn't sound very good. When I took it apart I was surprised to see that the vast majority of it was empty and that the circuit board was only 6cm x 4cm! That gave me an idea, since one of my previous projects was getting a second battery on the inside of the calculator, I can use the original battery bay to fit the circuit board in!



Of course it became a larger project than I expected. When I tried to turn the calculator and the Bluetooth module on at the same time, I blew the fuse that was originally for making sure when there were two batteries that nothing would catch on fire. Since I don't have a second battery anymore there's no need for the fuse so I just took it out and bypassed the connections. Unfortunately, without the original battery in, the calculator won't charge because one of the battery terminals wasn't connected so the calculator couldn't tell if the battery was safe to charge. Therefor I had to take the calculator apart and solder that contact to the battery bay. This took forever because I had a tiny bit of solder in a crevice shorting two contacts and I couldn't clean it! Thankfully, due to Nik's pro tips, I was able to get it wiped off cleanly eventually!



Next I cut down the speaker's circuit board so the length and width was small enough to fit inside the battery bay. I de-soldered its battery contacts, the 3.5mm input jack, the on/off switch and mic in order to make the height short enough as well. I re-soldered the mic on so it was facing directly up rather than to the side so it was more space efficient. I have no idea what kind of board this is, I couldn't find it online anywhere (although I didn't look too hard).



I was originally going to just short the on/off switch so it was always on, but I decided to extend the switch's reach with wires then hot glued it where a charging station contact use to be. This means I can turn it on and off without opening the battery bay! Unfortunately, I didn't glue it very straight so it's difficult to get the switch in the off position. It's not that big of a deal so I've just left it this way for now.



Since I don't have a speaker small enough to fit inside the battery bay (yet), I have to leave the battery door open while I connect the original speaker. I hooked up the circuit board's battery contacts to the battery bay (since they conveniently both use 3.7v Li-ion batteries) and it powered on! I connected it to my phone via Bluetooth and successfully made a phone call to one of my friends! I can also play music (even if it is only mono rather than stereo) over Bluetooth or even a micro SD card! I saw on the board a port marked FM which may mean the board supports FM radio as well? I may look into hooking that up sometime!



In order to get this project fully complete, I just need two things. First, a speaker small enough to fit inside the calculator. Second, I need a diode so the speaker circuit board doesn't get damaged if I forget to turn it off while the calculator is charging. I'm not sure what diode I need. The board takes 4.2v max and about 240mAh max. While looking at Digikey I saw fields like Voltage - Forward (Vf) (Max) @ If, Current - Reverse Leakage @ Vr, and speed but I have no idea what those fields mean or what I should choose for them. I'd appreciate it if someone could help me out here!

that'd be cool

I'd love seeing people call their parents/comrades during school without getting their phones/watches taken away. But you can't play sound on a TI-84+ CE, only older calculators!

Made some progress today! Instead of going for a purpose built speaker, I took a cheap contact microphone, connected it to the shell of the calculator, and used that as my speaker! It works fairly well for phone calls so long as it's not too noisy in the room. I even managed to get it just underneath the wireless receiver so the calculator should still wirelessly charge!

(Click for full size)

I made the connection from the contact microphone to the Bluetooth speaker circuit board just some pins I could easily take off and replace with a larger, louder speaker if I wanted. Then I closed it all up and tried it out. It works pretty well! I was able to have a whole coherent conversation with my friend over it! Thankfully the mic isn't impacted by the battery bay cover and my friend informed me that the sound quality was actually good on his end. I still haven't tried charging the calculator because I still need some help figuring out which diode I need, but overall I'm pretty happy with how this has worked out! Here's what it looks like in the battery bay:

(Click for full size)

OMG I'd love to make a program that could interact with that speaker/mic so that you could toggle the volume/enable speaker mode.

Me too, unfortunately there's nothing I can control on the calculator that would allow me to control the board. There is one unintended feature I notices, for some reason the battery door bulges in one spot. When I press down on the bulge it actually activates the play/pause button so that's convenient!

During HCWP last night I discussed with geekboy101 about what diode I would need. As it turns out, I don't actually need one because it wouldn't stop any potential damage if the calculator was charging. Unfortunately, there's no way to know for sure if any issues could arise if I left the bluetooth circuit board connected while I charged the calculator so I just need to be sure I disconnect the circuit before charging my CE.

I guess that means this project is done! I'll let you guys know if there's any updates about this!

I just published a video showcasing this project! I cover the build process, play some music, and even answered a phone call!

I was right to be cautious about starting this project. Backlighting the keys was by far the longest, most tedious calculator mod I've ever done.

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In my last update, I said I was holding off this project because I couldn't find LEDs that drew so much current. Turns out if you just reduce the provided voltage, the current draw falls dramatically! In the end, all 50 LEDs only drew ~30mA total instead of the expected 500mA which saved me when it came to wire thickness.

So what LEDs did I end up getting? If found a seller on Amazon who solders leads onto SMD C0402W LEDs which are super bright yet tiny which allowed me to fit them into each key without modifying the rubber membrane. I couldn't just hook the LEDs directly to the battery though. After testing a single LED on the battery, the LED got so hot it melted its own solder in just a few seconds. After a quick search, I discovered how to make a voltage divider circuit. Now, as a non-electrical engineer, this is the most useful, coolest circuit I've ever seen! I set up the divider so it turns the battery's max voltage down to just 3v. I'd like to replace this divider with a voltage regulator, but I just haven't spent time looking into one.



So I had the LEDs and I had the correct voltage, now how was I going to manage all 100 wires? My first idea was to run all the wires up along the right side of the keypad, then cut an empty portion of the PCB to allow room for the wires to come around the other side and connect to the voltage divider. This was a dangerous and terrible idea, but I didn't know that at the time. My first mistake was not disconnecting the battery while working on the PCB. I didn't know there was such a thing as a power and ground plane (which is a plane of copper that spans the entire PCB). Turns out the CE has 4 planes hidden in the PCB you can't see from the outside. When I cut the PCB, I shorted these planes and temporarily killed the calculator. I have respect for TI's engineers because after cleaning up the cut, the calculator booted without issue!



Now that I knew I couldn't cut into the PCB, I just had to hope that the wires would fit around without any modification. I spent about 7 hours hot gluing a LED into all 50 keys. Things were tedious but going smoothly overall, the cable management was even looking really good! I was oblivious to how much I had screwed up though...



One major problem with the LEDs I was buying at the time was that the positive and negative wires were the same color. Although I identified each end by connecting them to a battery, apparently I wasn't 100% accurate since several LEDs ended up being wired incorrectly! I replaced the incorrect LEDs but by this time, the beautiful cable management I did around the keys had been ruined by the rat nest where they all connected together. I didn't even have to test the mess in the calculator's shell to know there was no way it would fit. I spent hours trying to clean up the mess, but sometimes you have to realize your approach is just wrong and you better go back to the drawing board. I was devastated over 12 hours work on this project had been wasted so I left it for several months while school was in session.

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6 Months Later

I did learn some valuable information from the failed design. After testing the current draw and discovering it was 10x less than I expected, I realized I could just use magnet wire to connect everything rather than actual thick wire! This sparked a new design in my mind. Rather than having the LED positive and negative wires all exit at the same place, I would run all negative leads to the left side of the calculator and all the positive leads to the right side! These would connect to two power buses which would connect to the voltage divider.



I cut my losses by clipping the rats nest of wires away, then removing all the LEDs whose leads were too short to work with the new design. I ordered more LEDs from the same seller but this time they were different, now each lead was color coded! This made my job one step easier since I didn't have to test every LED to figure out which lead was positive or negative. It still took another 7 hours to undo my mistakes and implement the new wiring design. The new design worked spectacularly! I did wire up two LEDs backwards (they were reused, non-color coded ones from the previous design), but they were easily fixable since there was no rat nest to deal with! It was so satisfying when I connected a 3v battery and every single LED lit up!



I managed to stuff everything together (barely) and got to turn the backlight on for the first time! It looked alright but the real test was this evening, and boy it did not disappoint!



It definitely diffuses light better through the lighter keys than the darker ones but it's good enough to use it at night!



This was by far the most amazing, but most painful mod I've ever done. Total I've spent over 24 hours total researching, planning, and building this project over the course of a year. If I were to try this again, I definitely would not use LEDs. Instead, some sort of glow-in-the-dark compound would be significantly easier to work with.

This is an awesome mod but in the end, I'm really just glad it's over and I can use the dumb calculator again.

This is awesome! I'm glad you were able to get this working. I love the pictures and it looks awesome! Great job.

Whoa. That shows dedication to your project, and the result looks pretty nice

Very Christmassy indeed - congrats!