Solar powered

[samnmax777]

I got to thinking out of boredom "How else can I modify my calc?". And I know it's a relatively cliche idea, but what about a solar powered calc that can also store collected energy? My idea is as follows: attatch a panel(s) similar to those on cheap $2 calcs and connect it to a capacitor, that way it can be used even indoors with less lighting (since I assume the calc holder will spend some time outdoors). Since this is just a barebones idea, I would like to know what you think of it.

[c_plus_plus]

why dont you replace your bateries with rechargeable and wire the solar directly to the compartment?

[samnmax777]

That way you can run the calc virtually batteryless, or at least while using significantly less battery power (if set up properly). It's not really a matter of being able to recharge batteries (although I figure why not combine the two ideas?)

[Raster]

Youve got to understand those $2 calculators dont pull alot of current at all... I would say about 0.1 amp or less. but the TI calculators pull something like 0.5 amps. If you were ever to use solar power, try to find like these solar panels used on boat batterys to keep the battery fresh through the winter.

Think of it this way. Can you run your MP3 play with a watch battery? only for like a couple of minutes.

Sorry correction.
The TI calculators run at about 100mA and the $2 calcs run at like 10mA

[c_plus_plus]

If i remember my electronic equations corectly, couldn't you run 10 of the $10 calc's solar panels in series to make 10x the curent? Also, arn't TI's Scientific calcs runing on solar?

[todlangweilig]

That would be 10x the voltage, same current. You would have to put them in parallel for it to increase current.

You might want to try using one of the following:

Several small solar cells(2"-4") that are sometimes hooked up to a small motor, i dunno if they would have enough current though.

Another idea is what Raster said, which is probably the best idea. They put out something like 15v @ .350amp, Just hook it up to a 5v regulator IC and you should be good(be sure to check the max input voltage of the regulator first). The biggest problem is that they are costly, like $80 for a 5 watt panel.

Third idea is a solar power walkway light, the ones people have in there gardens. You might be able to find some for cheap.

[samnmax777]

Could I use a transistor to amplify the current? And if so, how would that affect the amount of stored electricity in the capacitor(s)?

[todlangweilig]

Sure, but you're not going to be able to create more power that you have avaliable or anything. So forget about the over-unity dreams.


This is what i would suggest:
solar panel --> low voltage alarm --> voltage regulator --> capacitor --> calc

Get a solar panel that will supply enough power to be used indoors. The voltage alarm is to signal when there isn't enough voltage to run the voltage regulator. When it goes off, it would be time to turn off the calc or make sure the panel is getting more light. The voltage regulator is to reduce and smooth the voltage so it is acceptable to the calc. I would use one like the LM7806, a 6v regulator with an input of 8 to 21 volts. The capacitor is to smooth any voltage drops and power the calc. Keep in mind, from what i have been able to calculate, the caps will only last for ~20 seconds or so. With the system I have outlined, you should have reliablity approaching that of using batteries. The only thing im not really sure of is where some diodes are going to have to be placed in order for things not to discharge in ways not intended, maybe more knowledgable members can help me with this.

5.5v 1 Farad Capacitor
Low voltage alarm

I would buy 4 1 Farad caps and use them in a series-parallel configuration:

[DigiTan]

Calc DBS was configured to automatically switch back to battery power if the external source dropped under 8 volts. Using a different regulator, you could get it to switchover at a lower voltage.

[todlangweilig]

That would work pretty well. Do you have any info on it? Or is it just the same thing as the e-16 on your website?

I just did some testing on my calc and came up with some interesting results. On my 83+, the max amount of current i could pull was ~16mA, at 6.3v no load. At the home screen it was about 3mA and a little key movement was about 5mA. I made a program to do pointless calculations and I did some graphing, both topped out at 16mA. I tried archiving a 9000 byte variable and that was around 10-14mA, I can't quite remember.

I seem to recall that writing the OS uses the most power, but would it take the same power as archiving? It should be the same rom chip correct?


If the calc truly uses this little amount of power, one can use some of the cheaper solar panels. I would imagine somewhere around 1.5w or so would do the job nicely. There were plenty of them on ebay for 10-20 bucks.

[DigiTan]

They're similar, but that project switched on an either-or basis where you couldn't run external and battery power at the same instant. Calc DBS draws from both sources based on which is the strongest of the two at the moment. I still need to draft the schematic for it. But it would help keep your contrast steady even with pesky clouds hanging around.

[todlangweilig]

Does it draw from both sources at the same time? Or does it draw from the external source only when its higher then 8v?

[DigiTan]

There's an even 50%-50% balance when the external source is at 8.1V. Half a volt higher or lower and the power will come almost exclusively from one source or another. You could lower the balance point to maybe 6.7V for smaller solar cells by removing the AC filtering stages that are in there.

[todlangweilig]

It sounds impressive, I can't wait to see it. Do you have it all designed in your head? When do you expect to have the schematic drawn up?

[DigiTan]

Right now they're in some paper notes. I've been meaning to get back to it and scan it or something. I'll have most of the day free Saturday so I might squeeze it in that evening.

[todlangweilig]

Cool, i hope you find the time to do it.

i was thinking some more, would your design work with only one power source? I was thinking if i am in math class and i have a constant light source. I dont want to have to pull out batteries as well as a solar panel to use my calc.

[samnmax777]

I would like this to be a universal module, so if anyone could give me any ratings on the higher end calcs (83+SE,84, and the 68k calcs) I would greatly appreciate it. Personally I am going to use this on my 85 and/or 86.

Secondly, I found this panel: http://www.4lots.com/index.asp?PageAction=...PROD&ProdID=333

I figure I can use resistors to reduce amperage, but I think it would have a dramatic affect on the voltage (I'll have to calculate it later)

Note: I am going to build/design this without calc DBS, I still don't know much about it, so once I look further into it, I can design it to be compatible with it.

[todlangweilig]

I only have an 89, ill see if i can't test it some time soon and get you the results.

Unless you plan on specially mounting your panel, may i recomend this one, for 3 reasons it comes in a case, it has presoldered leads, and it has a built in blocking diode as well as its about the same price.
http://www.allelectronics.com/cgi-bin/item...__CHARGER_.html

You don't need to be concerned with too much amperage, what you need to be concerned about is the voltage. The panel that both you and I have suggested have no load voltages of 8-9 volts. Of course the calc is designed for 6. I don't know how much voltage a calc can handle, and frankly i dont want to find out either. I hope you have a voltmeter as this will make your life easier.

Without a blocking diode, the solar panel may try to discharge your backup battery. You might want to concider this.

With the panel you/I have selected, it won't be compatible with the calc DBS. Well, it will but it wouldn't draw much power from the panel.

Obviously I'm not responsible if something bad happens to your calc.

[samnmax777]

Can you tell me how you test it (as well as any formulas you use)? That way I can find out the ratings of the 82,85,86, and possibly the 89T, if my brother lets me even touch it.

[todlangweilig]

I can test the 82. 85, and the 86 as well. I don't know how accurate of a reading I can get you on my 85 because its overclocked. Ill try to slow it back down to what its supposed to be.

The 'formula' for testing them is pretty simple, one gets a 6v power source (batteries,etc) and an ampmeter that readings in mA. Hook the ampmeter in series with the power source, attach it to the calc, and read the meter. Thats all there is to it.

little schematic
!|!|+ = battery
(A) = ampmeter
[calc] = calc
| or ---- = wires