[time-nuts] beaglebones, time, web services

[Jim Lux]

On 7/4/15 11:55 AM, Mike Magin wrote:
> Somewhat new time-nut here (had one of the Samsung-branded Z3805s for a
> few months as a house 10mhz ref, but it really got out of control when
> I acquired a Wavecrest DTS, multiple frequency counters, an old Astron
> 1250a, a Lucent RFTG-u pair, etc.), thought I should finally de-lurk
> since I can perhaps offer some useful opinion on this.  Comments inline.
>
> On Sat, Jul 04, 2015 at 06:13:06AM -0700, Jim Lux wrote:
>> I've got a project I'm working on to make a sophisticated sundial
>> with moving mirrors.  I've got a batch of Arduinos that move the
>> mirrors to the appropriate places, given the current sun angle, etc.
>
> I guess you are making a human-readable sundial,

Exactly... I've got an array of mirrors on az/el mounts (two servos 
stacked) and the reflection from the mirrors on the wall forms the display.





I was thinking recently
> about building a computerized mean-solar-noon tracker, just to see what
> sort of accuracy I can get.  Haven't decided between a cheap fisheye
> camera behind a dark filter (welding lens?) versus a sort of slot-lens
> (like a pinhole, but to tolerate the seasonal change in north-south
> elevation) with a wide-range light sensor (CdS or a modern ambient light
> sensor IC).

How accurate do you need to be..

two/four solar cells with a hole that projects an image of the sun on 
the cells, and compare the outputs (classic sun sensor for a satellite)

spinning mirror and fixed solar cell, timing of pulse tells you where 
the sun is

camera with a wide angle lens, and then do multi-pixel centroiding (0.1 
pixel is easy)

camera sensor with a plate with tiny holes in it, with the spacing of 
the holes slightly different than the pixels, so the "sun spots" have 
slightly different coverages of each pixel.




>
>> I've got a beaglebone that runs some python code to calculate sun
>> angle based on time
> [...]
>> Or are there libraries that make this more cookbook? (the little
>> "getting started with beaglebone" book talks about flask)
>
> In a previous contract job, I did some work with Flask, it's pretty
> nice, especially for the basic case of "make this subset of the URL
> space be handled by this function".
>
> I haven't set it up from scratch, but the Flask documentation seems pretty
> good, and if you're already familiar with Python, I'd highly recommend it.

Well, I got it to do the beginner "click here and turn on/off the LED" 
thing..

What I'd like, though, is to separate the "web serving" thread and the 
"doing stuff thread". I suppose I can fire off a thread from the 
webserver python.