This is a project I've always wanted to do but I never got around to making a topic for it. As you know, it's pretty darn hard to see what the keys are in the dark so I thought about back lighting them. As I was looking at Sam's TI 84 Plus CE tear down image, I noticed that the keys are slightly hollow and might be able to fit an LED!


(Click for full size image)

I foresee a few problems trying to put an LED in the keys.

0. I'm not sure where to find the products I need for this project such as a small enough LED that's the correct voltage (3.7v I think) or a thin wire that won't short if it touches other wire/metal. I also don't know the best way to wire so many LEDs together. Do you have an recommendations for this?
1. The keys may be too thick or dark to adequately backlight them with a small LED. The only solution I think could work is what Pieman suggested, 3D printing all new keys. However, I don't have the dimensions of the keys nor do I have a 3D printer.
2. If a LED does fit within the hollow space, it might mess up the grey rubber membrane and cause buttons to stop working properly. It might work to cut into the rubber but I think you could easily risk cutting in too far. Does anyone have any suggestions for that?
3. The arrow keys are a very strange shape and the top 5 buttons are thinner than the rest. I'd think either those need a different type of LED (which may not be as bright) or can't be backlit at all.
4. How are the LED's going to get power? I have a few ideas for that
  • Connect the lights directly to the battery leads. Then remove one of the metal contacts (the one at the bottom of the CE that's used for dock charging) and replace it with a switch. This switch will be used to turn the backlight on and off, it'll be recessed so it wont interfere with the slide case and wont be accidentally toggled when you're using the calculator outside of the slide case. This could be a bit difficult, though there are plenty of holes and spaces in the PCB so I don't think wire management would be too bad.
  • (I have no idea if this'll work) Connect the lights to the USB leads. That way the backlight only turns on when the calculator is charging.


Of course, before I go ham and try it to my own CE, I need to do some tests first. Sam (or anyone with a TI 84 Plus calculator keys), if you still have your calculator apart, could you see how well an LED will shine through the plastic? (the dimensions of the LED doesn't matter right now) Also, could to take a picture of the back side of the big grey rubber key membrane?
I'd love to see developments with this project. I love the idea and I wish you the best of luck Very Happy
(Just ask TI to develop a variant for it. Razz)
Just for future reference, Mateo recommended surface mount LEDs such as super small RGB and provided PDF. Also other lights which have great specs.
Commandz recommended having a few big LEDs then using light pipes.

Thanks guys! Very Happy
Or, paint the numbers with glow in the dark paint. Boom, problem solved, with no electricity usage!
SM84CE wrote:
Or, paint the numbers with glow in the dark paint. Boom, problem solved, with no electricity usage!

I second this idea!

Haha, anyways. This actually sounds like a great project. If you're actually able to accomplish this it would be awesome! I've never even thought of a backlight before, mostly because it sounds like you'd break your calculator in the process...
This is an interesting problem. Mounting an LED on each key and wiring them all up is probably a bad choice- it would be extremely fiddly and probably unreliable, plus it would be hard to find space.

There are two choices for backlighting in products designed that way: either an LED per key, or a diffuser between the board and keys. Using an LED per key is a relatively simple solution from a materials perspective because they just become part of the electrical assembly, but it's infeasible to try to do the same thing here- it would require a whole new board to either mount LEDs on the front side inside the contact area or cutouts for rear-mounted LEDs.

A diffuser is tricker in terms of materials, but potentially feasible here. The keys are kind of concave on the inside meaning there isn't much space for light to leak to the inside edges between those walls and the opaque key membrane.

Keys are easily the simplest piece of all this to replace, since they're simple plastic pieces. I'd start trying to design replacement keys that permit a diffuser to fit on top of the membrane and have some kind of transparency.
I'm not sure what you mean by a light diffuser that can fit between the keys and the membrane. Nothing I found online looked practical. Could you explain what you're talking about?

Quote:
Keys are easily the simplest piece of all this to replace, since they're simple plastic pieces. I'd start trying to design replacement keys that permit a diffuser to fit on top of the membrane and have some kind of transparency.
That's going to be fairly difficult, like I said above I don't have access to a 3D printer so I can't just print out new keys.
Many Cemetechians own 3D printers, perhaps if you designed the new keys someone could 3D print them and mail them to you.
  
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