Has someone considered making their prism slimmer? After taking the back off on mine I am convinced it could be so much slimmer. The empty space is created everywhere to accommodate the aaa batteries, so if we could have some slim rechargeable pack instead so that they just occupy the hight up to the protrusion of mini USB and 3pin ports that would shave off so much from the thickness of this unit. I realise the two copper coil connections for aaa batteries will need to be bend away or unsoldered and some circuit connection created to the usb port recharging which may be challenge in itself so all your thoughts and inputs are very welcome.

Making it slim would be number 1 goal.
Recharging via usb follows from the above presumably.
If the new back plate could be designed for 3d printing it would the best.
I imagine the design can be adapted to hold the original front cover same way it is now or with options for customised front covers.

Some options for skipping reset or integrating it with the new battery circuitry may be considered. I imagine the battery pack may go over the space where current restart button is positioned.

Who is the best person here to discuss 3d printing side of such a project please? Many thanks for all the support you can give
Geekboy and I both have experience with 3D printing and own our own 3D printers (see https://www.cemetech.net/forum/viewtopic.php?t=10958). I have designed and printed a slidecase for the TI-84 Plus family, and I'm hoping to try to do a full case at some point. You certainly could do what you're describing; one of the main reasons the TI-Nspire, TI-84 Plus CE, and HP Prime are so much slimmer than previous calculators is because of those rechargeable batteries. Yes, you'll need to add a charging/power conditioning IC along with the battery, but that's nothing particularly novel, and TI even makes a DIP IC for this if you're not comfortable with SMT soldering.
KermMartian wrote:
Geekboy and I both have experience with 3D printing and own our own 3D printers (see https://www.cemetech.net/forum/viewtopic.php?t=10958). I have designed and printed a slidecase for the TI-84 Plus family, and I'm hoping to try to do a full case at some point. You certainly could do what you're describing; one of the main reasons the TI-Nspire, TI-84 Plus CE, and HP Prime are so much slimmer than previous calculators is because of those rechargeable batteries. Yes, you'll need to add a charging/power conditioning IC along with the battery, but that's nothing particularly novel, and TI even makes a DIP IC for this if you're not comfortable with SMT soldering.
thanks, Kerm. I'm not sure which ti module would be the best, the one i found by ti seemed to have so many connections that i started doubting i would be able to know how to wire or program them. On ebay there're things like this TP4056 1A lithium-ion Battery Charging Management IC Module USB Charger Board which could be easier to wire without too much bulk or am i wrong please?
Trying to understand how wiring with rechargeable batteries would look and getting really confused. Maybe i am looking at wrong boards to begin with... Looking at tp4056 versions i can see how i can have + and - inputs as solder points or mini or micro usb slots on one side and on the other side battery + and - as on this link for example: http://pages.ebay.com/link/?nav=item.view&alt=web&id=321400539694

I was hoping to reuse existing usb input on the prizm itself and solder its +5v and grounds with two wires connecting to + and - inputs on the above board. I imagine it would work and i could even unsolder the micro usb port on the same board to keep it low profile. Please let me know if it is not going to be possible as i have no experience with this.

The other part confuses me even more: bat + and - points on that board then need to be connected to the battery but the battery contacts are connected to the calculator's battery contacts which i recall from the time I opened the calculator are connected to a few other places like the keyboard ribbon first and last couple of pins and I assume to the usb port on the calculator itself so i started worrying now that the new charging board's inputs and outputs points will be effectively connected with each other so I'm getting confused how it would do anything. Please kindly share your thoughts and expertise on this - I would like to learn more about this if at all possible for this calculator to be modded for rechargeable battery pack reusing its existing usb port... Many thanks in advance
I tried to sketch what my worry is on the below picture - will it be a problem to reuse the existing usb port? On the schematics on the right I drew in green what I believe the existing conncetions are on the calculator between its USB port and battery contacts - so I'm worried that the charging module will be prevented from properly regulating anything as usb socket is connected to the battery already... Or will it still work somehow? Or shall I consider not using existing mini-usb socket on the calculator and must use a separate socket just for charging... i.e. the back plate will have existing socket as is and another one for charging. On the other hand how is this calculator handing being connected to usb and combining its power with the batteries as observable from averaging out of the voltages reported by the calculator...


I look forward to your comments on this please

Many thanks in advance
One other problem I started realising some time ago but forgot to ask here was - most USB charging is 5V but actual batteries are ca 3.7V so will not be enough voltage for Prizm or at least the OS will consider it not enough... unless something else is added to transform the voltage or some other solution but I still would like the thing to be charged by USB...

I also wonder if moving this post to projects area would yield more comments...
Almost all devices with rechargeable batteries (at least lithium-ions) have a dedicated chip which controls power management and charging. I'm not very familiar with the Prizm, but it's possible that instead of being a chip by itself, it is integrated into another chip. Lithium-ion batteries have very specific requirements on what kind of charging voltage they take, and are a fire risk if charged improperly, so this chip pretty much eliminates any problems.

If the calculator needs 5V for something, for example the TI-84+-series and Nspire CX use something called a charge pump, which (I think, someone should confirm) is the same as a DC-DC converter, which is a fancy and useful device that makes a bigger voltage from a smaller one. If the Prizm refuses to run on 3.7V, either due to it complaining about batteries, or just plain refusing to run, then you may need to hook one of these up to the charge circuit.
TheLastMillennial shared some insights with me in the post https://www.cemetech.net/forum/viewtopic.php?t=16610 about doubling the battery and wireless charging
TheLastMillennial wrote:

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!


Does anyone know how to charge 4 x 1.2v Ni-MH batteries connected inside the calculator in series from 5V 500mA host please? I.e. what circuitry will be needed for that please?

Regarding separation from the existing USB port on the calculator: if the charging circuit above is not taking care of that will there be a way to use some diodes or mosfets to address that - can someone with the knowledge advise please?

I'm not sure if it is an encouraging observation or not but taking out batteries while being connected via usb to a host/power source the calculator does not shut down for some time (possibly due to large capacitors present on the pcb). Another observation is that the voltage measurement detected from addins systemcalls changes noticeably if power is supplied by the host to the calculator's usb port regardless if the batteries are in or out. It could be just how the software is designed. Measuring the voltage on the terminals where AAA batteries connect to the calculator (without batteries being in but with USB power being in) it keeps dropping and the calculator dies when the voltage drops below 4v. Connecting and disconnecting usb host to the calculator port does not seem to influence the voltage once the calculator is powered off without batteries as far as I can see. So to clarify the calculator powers down immediately if the batteries are taken out and USB port is not connected to power, however with USB power in the calculator is functional for while without batteries...
Does anyone know if there is a spot on casio fx-cg10/20 and/or cg50 which provides 3.3v constantly or at least when the calculator is powered on please?
  
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