Ooh, good price there. Much better than any I've seen elsewhere.

As far as that PCB mill goes, the inability to get solder mask and the inherently unplated vias are issues for me. Especially with the SMD components we're using, it would be very hard to do a clean construction job without soldermask on the board.

I'm slowly moving forward on the board but, haven't had much time to work on it in the past few days. The schematic is nearly done, I suppose, so that leaves the layout.

Looking great, Tari! By the way, would this $1.65 IC be worth it for us to use to replace our two power ICs?
http://www.ti.com/product/tps65721

Nice find! Fewer chips is nearly always better. Requires a bit of software support to get LEDs to indicate when it's charging etc (whereas the TPS61120 has some open-drain outputs for that), but that's no problem for our processor.

Just leaving some notes for tommorow as this train of thought just occurred to me and its been an idea nagging me for a while since I started reading on how simpliciti is structured to work.


SimpliciTi ihas the interrupts disabled during sending and receiving of frames. We need to make sure during this time the calculator thinks the network is jammed so that it will not try to send more data into the network when the wireless adapter is not able to receive the data.


That makes sense right?

Yes, that makes sense. Luckily, that is very easy to do, but we'll need to be careful to signal "packet in progress" rather than "packet about to begin". That means we need to throw some fluctuations on the data/clock lines, but we can't do the simple thing and simply pull the clock line low before sending over SimpliciTI, then releasing it afterwards. I'll check my CALCnet source to see if pulling the data line low the whole time would do the trick.

Alrighty cool that has just been something nagging me from the get go as everything we are running is single threaded lol

I created a part for the TPS75621, then realized it won't work as I was hooking it into the schematic, since its DC-DC converter is a step-down converter, while we need step-up.

So we're discussing this on Have Calc, Will Program this evening; here's what came up:

- Bummer about that TI part; I don't see another option other than the two individual ICs.
- Geekboy noticed that the stencil place closes on October 21st for a few weeks; does it fit into your schedule if we try to finalize a preliminary board layout before then, Tari?
- We both filled a cart with flux and solder paste on Deal Extreme for working on this once boards and stencils arrive.
- The CALCnet protocol only listens for clock fluctuations to determine network activity. Therefore, we'll have to twiddle it up and down while sending radio data to avoid lost broadcasts

Anything else?

Edit: Since we're going to be doing this out of our pockets anyway, and this is something a lot of people could use both for wireless computer-calc linking and calc-calc linking, would there be a point in making a KickStarter for it? We discussed it on HCWP as well.

i agree with the kick starter. Doing the math its going to cost us about $70 for each of us to just get a prototype board. Then another $35 to get a finished board.

I agree with the kickstarter, or at least something for donations for this. Especially since you already have a prototype in the works, and the actual possibility of this working.

Thanks, and I do indeed remember reading that prototypes in the works are a required part of kickstarter now. That is, no more kickstarters for projects that are still thoughts in someone's head. However, there are also a few caveats:

- Based on all of the people who chatted with me about wireless CALCnet at World Maker Faire 2012, we need to be diplomatic. Perhaps 50% of them were students who wondered if they could "chat" in class using this, to whom I often made a remark about Cemetech and myself being staunchly opposed to cheating. Another 30% were adults joking around that a wireless version would be (too) perfect for cheating. The remainder seemed to be educators who said that if there ever were a wireless version, to let them know so they could be on the lookout. They were only half-joking.

- That last group there is one reason that I dislike the idea of making it internally-mountable, at least from an ethics standpoint. I'm torn between the miniaturization love of a good hacker looking to make a clean, compact final project, and a teacher/author/student who wants to be an ethical member of society and pedagogy.

Well for the kickstarter version just make it external so its obvious that you can see it so people can't cheat. But make it so the adventurous and people with some knowledge could put forth the effort to miniaturize it into the case maybe?

That's probably the best, plus a disclaimer that we don't condone cheating. When we were discussing possible cases on HCWP, we realized that if Tari et alia can figure out a small enough board over a small enough Li-Poly battery, we can just heat-shrink the board and not even bother with a case. In that case, we would have a 1.25"x0.75"x0.4" (maybe?) board+battery sandwich with a 2.5mm stereo plug sticking out, heat-shrunk, with a microUSB port exposed somewhere. That dongle would hopefully be obvious enough.

i agree wholeheartedly with the disclaimer. Also yeah, make it a tad obvious, and something sticking out of the top ( or bottom) of a calculator should be noticeable by a teacher. That will hopefully discourage cheating enough. I will however be incorporating this into an old mod of mine, assuming i ever find my box of parts.

Excellent, I hope you do. By the way, we can probably lower the price of construction even more by having an on-board 2.5mm stereo jack (something like this, for example, and let people use their unit-to-unit cable. Actually, that might not be a good idea, now that I think about it, since the newer calculators only ship with the miniUSB unit-to-unit cable.

me too. But yeah, I don't think the unit-to-unit cable would be a good idea, wireless all the way, plus finding those cords suck sometimes. I guess maybe include that to add yourself on the board, or make it a second model of the device with that on it?

My TI-84 Plus (bought in August IIRC) didn't come with a unit-to-unit cable at all; just a PC cable.

I can try, but no promises. Consistent prodding would help keep me on track.

How much stuff and how expensive is it? I'd love to have some solder paste for my own stuff, but shipping tends to be rather expensive because there are regulations covering it (I believe as a hazardous substance, but maybe that doesn't apply to lead-free solder).

Maybe, but I think it's better to do the first-stage prototyping out of pocket. If there's significant interest in doing a larger run once we've hammered out the principle of operation (that is, done a prototype and identified the inevitable problems in it), a kickstarter would be useful.

As far as a case, I've thought a 3d-printed design that can fit right on the end of the calculator would be nice. In that case you'd want two variants (for the 83+ case and 84+ case), but there's no reason they couldn't both be compatible and just a little uglier when attached to the mismatched case.

TI has a useful design note, DN019, on powering Low Power RF things

http://e2e.ti.com/support/low_power_rf/w/design_notes/dn019-powering-lprf-products.aspx

that looks like a good overview on powering TI parts, looking at the tradeoffs between linear and switching supplies.

RFDave, that is indeed a helpful datasheet; thanks for finding that. I'll give it a close read.

Tari, I think something that would fit on top would be a nice design (sort of the way TI's wireless gadgets fit on top of the Nspire?). For that, I suppose we would want a 2.5mm plug mounted into the case itself both to connect and anchor the device; might we also want to make it plug into the mini-USB port, just to anchor it? For that model, perhaps we could even do away with the battery and just leech power off of USB. I don't know if it's worth making separate 83+ and 84+ designs, but that would be one possible difference.

Edit: It looks like shipping is free. Here's what's in my cart at the moment, although I might make it less:

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