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HP Forum Archive 20

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I Wish HP Higher End Calcs Were Solar-Powered!
Message #1 Posted by Jeff on 30 Jan 2012, 2:54 p.m.

I don't know why they aren't. While the solar panels might not have enough capacity for real time use, they could be used to charge rechargeable batteries.

      
Re: I Wish HP Higher End Calcs Were Solar-Powered!
Message #2 Posted by Jake Schwartz on 30 Jan 2012, 4:11 p.m.,
in response to message #1 by Jeff

Hi,

Back in the early 1980s, I managed to hook up a small solar panel to successfully run the HP41 (except for the card reader) in ambient light. That panel was around 20 square inches - around the same size, or possibly slightly larger than the HP41 itself. I hope that cells have gotten much better in the past three decades or so to do the job.

Jake

            
Re: I Wish HP Higher End Calcs Were Solar-Powered!
Message #3 Posted by Garth Wilson on 30 Jan 2012, 7:37 p.m.,
in response to message #2 by Jake Schwartz

The 41 manual says it takes about 20mA when a program is running, which is a lot to get from calculator-sized solar cells at 5 to 6V even in the sun. Common indoor lighting in a house will be well under 1% of the brightness of sunlight. The 50g, inspite of bigger batteries, has very short battery life compared to the 41.

      
Re: I Wish HP Higher End Calcs Were Solar-Powered!
Message #4 Posted by Eric Smith on 31 Jan 2012, 3:51 a.m.,
in response to message #1 by Jeff

Why they aren't is that photovoltaics not only don't supply enough current to run the calculator, but also don't supply enough to charge a rechargeable pack in any reasonable interval. They barely supply more than the self-discharge of NiCd and NiMH (except the low-self-discharge NiMH). The amount of power you can get from 10-15 cm^2 of photovoltaics even in bright sunlight is negligible.

Photovoltaics only are sensible on calculators with *extremely* limited processing power, which means not beyond low-end scientific or business calcs. You might notice that on solar-powered scientific calculators, the transcendental functions are often very slow. Such calculators use ultra-low-power masked-ROM microcontrollers which have very little memory and run at amazingly slow clock rates. For obvious reasons that is unsuitable for high-end calculators.

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