[TriEmbed] AllPixel Project Documentation

[dan]

Good point, Pete. This would certainly not be preferred if high accuracy is
desired. But for a quick and dirty option, this may suffice. Perhaps if you
included some kind of sampling and averaging, it would be a little bit
better.

-Sent from my phone
On Aug 27, 2015 10:57 PM, "Pete Soper via TriEmbed" <triembed at triembed.org>
wrote:

> One thing to keep in mind with this and nearly everything else on a
> Raspberry Pi is that your program can be preempted at any time. Literally
> in the middle of one of the Python statements control may be yanked away
> and given to another process, then passed back to finish that statement an
> indeterminate time later. Between device interrupts and processor
> scheduling ("time slicing") with background daemons, there is a blizzard of
> program interruption going on more or less randomly. Depending on the
> system load (or just plain chance) you may see this never or a lot or
> anything in between. So don't be surprised if the simple code from the
> Adafruit tutorial below puts out some very funky numbers occasionally (i.e.
> they're completely crazy with respect to what you know the sensor should be
> reporting). There are ways to make the code immune to these kinds of
> errors, but it adds complexity. A relatively accurate time reckoning scheme
> for Python on Linux is in "answer 54" on this page
> <http://stackoverflow.com/questions/231767/what-does-the-yield-keyword-do-in-python?rq=1>.
> I just confirmed this works fine on my regular Linux system and think it
> ought to work just as well on an RPI. One way to reject bogosity is to toss
> a number that represents an impossible change in sensor readings. That is,
> if you know the sensor can't be reporting a room temperature of 70 degrees
> one moment and 90 degrees the next, you can toss the 90 degree reading. But
> this adds complexity and it won't be long before you want to use an ADC
> chip. :-)
>
> And concidentally, tonight at Splatspace Geoff Tattersfield facilitated a
> session about using an MCP3008 ADC chip with a Raspberry Pi using the SPI
> bus. Folks went through this Adafruit tutorial
> <https://learn.adafruit.com/reading-a-analog-in-and-controlling-audio-volume-with-the-raspberry-pi>
> .
>
> -Pete
>
> On 08/27/2015 09:32 PM, dan via TriEmbed wrote:
>
> I love it! And a very nice write-up too :) I'm definitely a fan of using
> the lights to show different kinds of information (weather, time, scores,
> etc.) I really like your weather display. Maybe you could have chasing blue
> lights when it's going to rain, hehe.
>
> As a hardware nerd, I especially like the photoresistor RC timing trick.
> I'd have never thought of that, but it makes perfect sense. I'll have to
> keep that in mind for other projects :)
>
> For those curious, the adafruit article Chip linked to explains how you
> can read restive sensors (like a photocell) using a Raspberry Pi's GPIO
> pins without needing an external Analog-to-Digital converter module. For
> simple sensors, this would be a great way to interface them to the Pi on
> the cheap.
>
>
> https://learn.adafruit.com/basic-resistor-sensor-reading-on-raspberry-pi/how-it-works
>
> Thanks very much for sharing! Please keep us up to date if/when you make
> any changes/additions!
>
> -Dan
>
>
>
> On Thu, Aug 27, 2015 at 7:24 PM, Charles McClelland via TriEmbed <
> triembed at triembed.org> wrote:
>
>> All,
>>
>> From the last meeting, here
>> <https://www.hackster.io/chipmc/awesome-led-entertainment-center> is the
>> documentation for my Entertainment Center LED Geek makeover.  Comments and
>> suggestions are welcome but please be kind as this is my first time
>> programming in Python.
>>
>> Thanks,
>>
>> Chip
>>
>>
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