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Geek Culture / I overclocked a pocket calculator!

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Dark Java Dude 64
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7
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Joined: 21st Sep 2010
Location: Neither here nor there nor anywhere
Posted: 15th Jul 2017 06:07 Edited at: 15th Jul 2017 06:09
With a flashlight! At least, I'm pretty sure that's what happened...

Back a couple months, I went on eBay and arbitrarily ordered a little credit card sized calculator like this one. It was only a dollar with free shipping from Hong Kong! It finally showed up today. They gave me a pink one!

Anyway, the calculator is only solar powered and has no internal battery, so supply voltage will be directly related to how much light the solar cell is receiving. I noticed something interesting! Some of the operations, namely dividing and square rooting, take a noticeable amount of time to complete. In darker environments, they take even longer to complete.

So I did some research! Apparently, most pocket calculators, even the most basic ones, use a microcontroller. It's very basic, sporting only a 4 bit processor that operates using binary coded decimal mathematics, a masked ROM, and I presume some archaically small amount of memory. According to some datasheets, the processor has two modes: a standby/waiting mode where it runs at 18 kHz, and an operating mode where it runs at 200 kHz. These little processors also use a simple resistor/capacitor oscillator for timing, instead of the much more accurate and higher speed quartz crystals most processors use. Because of this, it's quite feasible that the actual clock speed at which the processor is running varies with supply voltage, and hence, the amount of light the solar cell is receiving.

To test this, I took an ultra bright flashlight and put it right up against the solar cell and did some of those slower operations. Sure enough, the calculator is super fast! In very dim conditions, the calculator would take around 2 seconds to complete a square root. With the flashlight, it's almost instantaneous!

So yeah, I think I've overclocked a little pocket calculator. It's made my day!
Yes!
Phaelax
DBPro Master
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Joined: 16th Apr 2003
Location: Metropia
Posted: 27th Jul 2017 16:07
Did you really overclock it? Or is it just now getting the light it always needed and now is no longer underclocked?

"I like offending people, because I think people who get offended should be offended." - Linus Torvalds
Dark Java Dude 64
Community Leader
7
Years of Service
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Joined: 21st Sep 2010
Location: Neither here nor there nor anywhere
Posted: 27th Jul 2017 20:27
Quote: "Or is it just now getting the light it always needed and now is no longer underclocked?"
Haha, that's probably about right. Now, I just gotta figure out how to render some 3D graphics on there...
Yes!

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