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Gadget Freak

Gadget Freak Case #271: Portable Weather Station

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armorris
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Platinum
Re: Well-Documented?
armorris   8/21/2015 2:22:31 PM
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Sorry about that. I didn't read it in detail. I just saw that it had schematics and code listings, which many GF projects don't have. I tried to say something positive.

Critic
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Platinum
Well-Documented?
Critic   8/21/2015 12:09:07 PM
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@armorris:

Well-documented?  Really?  I challenge you to find the part number for the anemometer.  There are other problems as well.  The parts list is incomplete, and the schematic has issues.

You can measure altitude or barometric pressure, but you need appropriate reference levels for each, which vary with the weather or altitude.  There needs to be a reference from a different source.

This is a cool project, but well-documented, not so much!   

78RPM
User Rank
Platinum
Re: Nice project
78RPM   8/21/2015 10:32:24 AM
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Hi, armorris, Charlieplexing is a method of addressing more LEDs with fewer pins. Charliplexing is named after Charlie Allen of Maxim. It uses the tri-state property of I/O pins, i.e., High, Low, Input (high impedance). There are a number of explanations of the technique online. Using the technique one can address n2-n LEDs using n pins. One does have to be careful of current limitations.
Another advantage of Charlieplexing is that it reduces the number of current limiting resistors, assuming all LEDs are of equal current. This would save parts count and board space. I notice that they use several resistor arrays.
One should be careful on the SOS function in that driving all LEDs at once could overload the maximum total current of the MCU.

78RPM
User Rank
Platinum
Re: Charlieplexing & Workmanship
78RPM   8/21/2015 10:24:47 AM
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BRedmond, I just clicked on Post Message below any other message post and it worked for me in posting a new subject. Were you logged in at the time?
I was looking at their code and it seems like they define THERMISTORNOMINAL as 10,000 ohms and assume that it represents 25ºC. Then they do an analog read on the thermistor pin and use the Steinhart-hart equation to calculate the temperature.

armorris
User Rank
Platinum
Nice project
armorris   8/21/2015 10:18:43 AM
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Very nice design, well documented, but experimenter socket-board is not suitable for long term use, as explained by others. I've seen many other GF projects that were built up like a permanent project, but using socket-board for the electronics. Makes no sense to me. I always use perfboard on my one-off projects. I save my (much more expensive) socketboard for breadboards only.

BTW, what is Charlieplexing? I've been a practicing electrical engineer for decades and I have never heard of it before now. Is that some kind of kludged-up multiplexing technique to save I/O pins? If that's the case, I have done it many times without knowing what it's called. Who is Charlie?

 

BRedmond
User Rank
Silver
Re: Charlieplexing & Workmanship
BRedmond   8/21/2015 9:54:26 AM
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I don't understand whyI can't initiate a comment, only reply to other people's comments.

I also can't cut and paste from the article while writing my post.  d'Oh!

 

a thermistor to measure the change in temperature and LEDs to display temperatures.

Are they measuring T or delta T?  I know that Mechanical Engineers are more often interested in delta T but it seems like a weather station is more interested in the actual temperature (unless you really do want to know that the temperature has dropped 20 degrees in the last hour).

78RPM
User Rank
Platinum
Re: Charlieplexing & Workmanship
78RPM   8/20/2015 11:42:31 PM
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You raise good points. Breadboarding is great for prototyping. I agree that if you want to haul this into the wilderness (like where I live) you would want solder connections. But Schmartboard offers a solder breadboard that mimics the breadboard. You could actually solder the connections after confirming it works. You just lay it on top of your breadboard and solder at will.

I also agree with your comments about inability to weld for most of us. But one can get framework hardware from Adafruit and Sparkfun. Just a suggestion to others.

As far as code writing: That's why we need to practice modular design. Just call a function that can be re-used.

Critic
User Rank
Platinum
Re: Charlieplexing & Workmanship
Critic   8/20/2015 4:22:16 PM
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I agree that they did a good job on the packaging, but it is what I would expect from mechanical engineering students.  I was surprised that they used a welded aluminum frame- not everyone has access to equipment for welding aluminum.

As for the electrical workmanship, I disagree that it was nice.  They used breadboards for making connections to components.  This is a quick and dirty way to make temporary connections.  It can be unreliable, because wires and components can get loose and break connection.  In the long term, corrosion could also kill the connections of a breadboard.  Because this is a portable weather station, the potential operating environment (possible bad weather) should have been considered.  There are better ways to make the connections.  One is with custom PC boards, which they could have made themselves for not very much money.  Another would be copper-clad vectorboard. 

Charlieplexing would have been a good multiplexing technique for them to learn about, but it would have made the code writing/development and design work more labor intensive.  It might have caused other problems, too.  Because they didn't run out of microcontroller pins, there wasn't really a good reason to use Charlieplexing.

78RPM
User Rank
Platinum
Charlieplexing
78RPM   8/20/2015 1:21:22 PM
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Nice workmanship on the construction. With that many LEDs, did you consider Charlieplexing them to reduce the number of I/O pins?

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