The inside of a cheap calc

Spyro543 · Member Joined: 17 Sep 2011 Posts: 129 Location: Ohio

My friend had a Sentry CA756, but the EXE button stopped working, and he gave it to me (but I can't fix it). These graphing calcs are about $20, with a very small screen and only 10 program spaces. Yes, 10. You reference them by using Prog, like Prog 1. It's looping capabilities are lbl, goto, ISZ, and DSZ. Sad, isn't it? And it doesn't even have a function catalog! You have to access function with a Shift- or Shift-Alpha- key sequence. To change the calc's mode, you have to press MODE, MODE-SHIFT, or MODE-ALPHA and a number. D: This thing is awful! So, without further ado, here are some pix!

Here's the awful small screen and the label that tells all the calc modes.

Sorry about this one being blurry, but here's the keyboard. As you can see, almost all of the keys have SHIFT, ALPHA, and SHIFT-ALPHA labels on them.

Here's a close-up of the arrow keys. Notice how they stole the "REPLAY" and "EXE" from Casio. Razz

The "screenshots" on the quick reference aren't even screenshots. They didn't even attempt to make them look real.

The battery. Notice how the calc only needs one battery to work, so they just glued foam to the other contact!

This is the inside of the calc.

The main (and only) chip is, of course, buried under epoxy.

Here you can see that foamed-up battery slot also has terminals running to the circuit board, just like the other one!

The only thing holding the LCD in is the back cover pressing against it. I can freely pull it out of its slot (that is too big, the LCD can wobble all around in the slot).

Another shot of the calc, this time with the LCD flopping.

You have just witnessed how awful this cheap, $20 calc actually is. It's definitely worth less than $20 Razz

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KermMartian · Posted: 24 Dec 2011 09:08:26 am Post subject:

Actually, I'm moderately impressed that a $20 calculator is programmable at all. I'm a bit curious what sort of processor/memory they have under that epoxy blob, whether it's something standard or custom.
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Ashbad · Posted: 24 Dec 2011 09:09:50 am Post subject:

KermMartian · Posted: 24 Dec 2011 09:15:54 am Post subject:

Definitely. To expand on my wondering about what sort of hardware is lurking under that epoxy, I'm curious how much this could be hacked and expanded. If a TI calculator is already a fun challenge for hacking, this seems like it would be an even bigger and potentially therefore more rewarding challenge.
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Travis · Posted: 24 Dec 2011 07:31:56 pm Post subject:

Back in the 90s, I saw a $20 programmable calc (Sharp, I think) in a catalog, but it was just scientific, not graphing. I wanted it but I later eventually settled on the TI graphing calculators I started out with, which probably eliminated my interest in the lower-level models.

I wonder if this calc is actually a rebranded Casio, given the similarity in the keys and the mode-number key sequences that many Casio scientifics used.
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KermMartian · Posted: 24 Dec 2011 10:32:57 pm Post subject:

Snipes · Newbie Joined: 24 Dec 2011 Posts: 6 Location: Lakewood, CO

Ashbad · Posted: 25 Dec 2011 08:45:48 am Post subject:

KermMartian · Posted: 25 Dec 2011 12:33:16 pm Post subject:

Snipes · Newbie Joined: 24 Dec 2011 Posts: 6 Location: Lakewood, CO

KermMartian · Posted: 31 Dec 2011 06:43:02 am Post subject:

willrandship · Posted: 01 Jan 2012 03:14:25 am Post subject:

I'd rather get a $30 86 from amazon, or a raspberry pi Razz

but I suppose if I already had one I'd mess with it. I've heard there are ways to get epoxy blobs off of those things with the right chemicals and whatnot.

http://www.amazon.com/gp/offer-listing/B00000JF53/ref=dp_olp_used?ie=UTF8&qid=1325405691&sr=1-1&condition=used

I rest my case. That's a lot more powerful.

And it seems there's a steady supply. I got my 86 for $30 4 years ago, and I've never seen a change in the lower prices. None of them are in non-working condition either.

Also, the thing I find most fascinating about calc programming over computer programming is how much is known about the hardware. We know these calculators so well that we make programs that far exceed the expectations people put on things 5 times faster. That's impressive. Imagine a PC world like that. Skyrim could run on a PIII. But it really requires the hardware specialization we only see in areas like this, where asm is really the most viable language, not C. C has a tendency to hide what slows it down the most on a low level.
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KermMartian · Posted: 01 Jan 2012 11:25:41 am Post subject:

Interesting, I didn't realzie that Amazon had those kinds of deals. I'm used to getting very inexpensive TI-83+s that require some repair. I wonder what they have in the way of Prizms.
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Kaslai · Member Joined: 16 Nov 2011 Posts: 172 Location: ???, WA

willrandship · Posted: 01 Jan 2012 07:58:37 pm Post subject:

My school doesn't get ripped off at all. They rent calcs out for $30 a trimester, so their investments are paid off in under 2 years. And those calcs are a lot more than 2 years old, most of them are 82s. It's nice to see the school being smart about products. They seem to be on a smartboard kick, though.
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Hmm...what to put here....