I've seen a few USB C mods for the TI-84 Plus CE but they all seem to have the same issue: they're charge only. This mod replaced the USB port. This mod simply added a secondary port.

Even if the mods above could get data transfer working, as I understand it, the breakout boards would only support either transmitting data or receiving data; OTG functionality would be lost.

I'd like to keep OTG functionality so I went on Amazon and searched for OTG adapters I could take apart. It took a bit of digging but I found this adapter which claims to retain OTG functionality! I noticed there's a catch though:

For those that understand USB better than I do, is the ideal USB C conversion mod (charging + OTG at the same time) possible? I'd like to get a clear understanding of why this may or may not work before I hack my calculator apart again.

I'd have to look into it in more detail, but what you're looking for is referred to as a DRD and a DRP in the specifications, for dual-role data (either UFP or DFP) and dual-role power (either source or sink) functionality.

Operating as a USB-C sink is relatively easy, because you only need to present appropriate pulldowns on the CC lines. Operating as a source (if you want to use a self-powered device) requires detecting a sink's pulldown and turning on VBUS, which requires at least a little bit of smarts. Operating as a DRD requires the ability to switch between CC pullup or pulldown, but is otherwise no more difficult than being a DRP.

TI's SLYY109 application note provides a pretty good introduction to the basic system requirements for assorted USB-C modes, where the relevant topology for your question is "USB Type-C DRP/DRD USB 2.0 without USB PD."

Thank you for all the resources Tari! It'll still be a little while before I can work on this project fully but I have a lot of motivation to do it now. I noticed today that the USB port on my calculator broke! The plastic piece that keeps the pins in place is missing now.

Here's my blue CE's port compared to my working, red Nspire's port.

Edit: TLM 1800th post!

This sounds like a great idea, and it certainly would be great to see the USB hardware updated a bit. Pardon my dumb question, but would the mod affect transfer speed at all (assuming you're able to still transfer files)?

I know that the Zero Calculator is supposed to have USB C, which I think might be the first calculator to intentionally have it? It'd be interested to see how your modded version compares to the Zero Calculator when it's released.

It would not affect transfer speed at all.

Yes, a few calcs (numworks/HP prime) use micro-usb but I'm pretty sure Zero is the only one using USB-C currently.

yea it wouldn't affect speed, but its still better in every other way

OK most of the circuitry details go over my head so I sought help from my electrical engineer friend, who ended up getting more confused than me because USB is a mess 0x5. Anyways, my friend figures that in order to get the rp/rd switch required for DRP, I would need an IC like the TUSB320 and configure it like Figure 8-7. I really would like to avoid adding in ICs so this project doesn't get too complex.

I started looking for other solutions and stumbled upon this Russian site (google translated) that showed pin to pin connections for a variety of different adapters. The closest I found to my application was a female micro usb to male usb c.

Click for full size

There's a few issues with it. First, I don't know if simply replacing the male connector with female connector is something I can do and still have everything work. Second, it doesn't seem to really follow the documents Tari provided so I'm skeptical it'll work the way I need.

Before I proceed, I'd like to understand if this project is feasible without an IC. If an IC is required then that'll add another learning curve and slow this project down a lot. If an IC isn't required, is the pin to pin photo I posted a viable solution? There's quite a few options on the website I linked, perhaps there's a different solution there?

I have been doing some research on this and have come up with a few ideas.

If an IC must be usd, the TUSB320 is the correct chip for the job. It is intended to adapt an OTG/DRP (dual role port) USB 2.0 port (which uses the ID pin) into a USB-C connector (using the CC pins). So if using an IC is the only solution, the TUSB320 is the way to go.

The main job is converting the CC pins of the USB-C port into a signal that the ID pin can understand.

For the ID pin, the roles are as follows:

ID pin pulled to GND: Calculator acts as USB host.
ID left floating: Calculator acts as USB device.
ID pin pulled to HIGH (I do not know if it is 5v tolerant, it may need to be 3.3v?): Likely, Calculator acts as USB device. Untested.

For the CC pins, the behavior is similar:

USB port intends to be USB device: CC lines are pulled to GND through 5.1k resistor.
USB port intends to be USB host: CC lines are pulled to 5v through a ~55k resistor.

There are 2 CC pins on a USB-C port, but for a USB-C cable, there is only 1 CC wire. This is intended to detect directionality (USB-C cable plugged upsidown or rightsidup). In the proposed solution from that Russian site, the one CC pin is connected to the ID pin through a 55k/5.1k resistor divider up to 5v.

If the connected device pulls the CC pin down to GND (indicating a USB device is attached), then there is a 55k/10.2k resistor divider on the ID pin between 5v and GND, essentially supplying it ~1v, which should be a logical low, making the calculator act as a USB host.

If the connected device pulls the CC pin up to 5v (indicating a USB host is attached), then there is a ~24k resistor attaching the ID pin to 5v, which should be a logical high, making the calculator act as a USB device.

Again, all of this is untested, and it seems the cable would now be directional, but the 2-resistor circuit is simple enough to warrant testing.

Looking forward to seeing where this project leads!

This has no OTG support but hey it might help you. https://redd.it/184r1qd

Thanks for bringing that to my attention! It looks pretty sweet and I'll reach out for more details!

Hi, I'm sure many of you have already seen, but Light Creations was successful in creating a USB OTG compatible USB-C mod for the TI-84.

The link to their results is below:
https://www.cemetech.net/forum/viewtopic.php?p=305740#305740