Subject:
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Re: MOC: Working solar powered rover and geiger counter
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 10 Feb 2006 19:32:26 GMT
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Viewed:
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2095 times
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In lugnet.robotics, Brian Davis wrote:
> I fear all I can do is gawk in astonishment. Getting a HV sensor to work off
> the RCX is truly an amazing acomplishment. But you've gone well beyond that,
> with the solar panel (I'd seen the earlier one on eBay), the powercan... and the
> low-power mode for the RCX!! This last is perhaps the most amazing to me, and it
> may be a modification I try to make. I'm curious if I could use this to "wake
> up" an RCX on a schedule, or when certain events trigger, and latch the power on
> until the RCX shuts itself off again (I'm thinking long-term monitoring of
> environments for weeks or months). I'll have to poor over the schematics, but
> I'll agree with Philo and others, very nicely documented.
This would not be difficult - if you scroll down to the bottom schematic, it is
colour-coded into sections according to function, with the last third of the
circuit being all that you need to make a switch to activate and run the RCX
from some external trigger.
>
> Do you have documentation (OK, schematics, internal pictures, or hints and
> tips on building them) for the energy cans?
I do actually. I'll put that on the list of stuff to add to the site. In the
meantime, a text explanation: the heart is four really really high density
capacitors, the ones I use are 10F 2.3V. Thanks to the relentless march of
technology, stuff like this that didn't exist a few years ago now not only does,
but is affordable :). Putting them in series creates a capacitor bank that is
2.5F 9.2V. A bridge rectifier is needed to charge the bank, since it can't be
charged backwards, I make that out of massively overspec (30A) schottky diodes
to minimise the voltage drop. Most of the actual circuitry stuff is related to
making a low-power charge indicator lamp that starts blinking when the EnergyCan
is fully charged. If you're using the RCX with NQC or similar language, you
don't really need that indicator lamp since you can read the battery voltage,
assuming you know what the diode voltage drop is between the caps and the RCX
internal monitor. Since it's starting to become a fairly impressive capacitor
bank when fully charged, I put a 1 or 2 ohm large sandstone resistor block on
it, so that in the event of a short, nothing will get too hot. This reduces the
efficiency slightly, but I think it's worth it. There is also a diode on the
output to prevent reverse charging if a power supply was put on the output. In
series if you want to protect the the power supply as well as the EnergyCan, in
parralall if you want higher efficiency by avoiding the voltage drop.
Alternatively, a simpler design is to drop the bridge rectifier and the output,
and have a single connection point that only works if you plug it in with the
right polarity (use a second indicator lamp to show if it is plugged in the
wrong way)
>
> And what type of solar cells do you use in the solar panel (efficiency?)
I forget the names of the different types, but the glass brown ones are low
efficiency and while cheap, are no good for this kind of thing. The blue/silver
silicon wafer ones are the ones - higher efficiency but more expensive. That's
where the main efficiency difference is, it varies less between cells in the
same camp, so finding cells of the right phsyical size is generally the higher
priority (I can't get the ones I used any more). I buy a larger number of
(supposedly identical) cells than I need, and test them with a multimeter to get
the best ones that match each other electrically the closest. (Matching cell
performance is actually more important than individual cell performance). There
is also NASA-style end of the silicon cell range, which have an efficiency edge
over the rest. These are nearly black (which I assume means the capture more
light, since they're reflecting less :). I have some of these to play with, but
the cost to make a mindstorms-sized panel of these would be large. Thanks for
reminding me about this - I have a better income now, so it occurs to me I
should look into the cost of making one with top-of-the-line cells, since I'll
probably want to build something for the NXT system, and every bit helps :)
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Message has 1 Reply:
 | | Re: MOC: Working solar powered rover and geiger counter
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| (...) Wow, why do I think this has the potential for extreme pain? In any case, I'm very interested in anything you can provide for the rest of us. You've done some really nice work, that the rest of us would now like to copy :-). (...) That's (...) (19 years ago, 10-Feb-06, to lugnet.robotics)
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