So after I built a focuser controlled by a joystick, and considered it a usability failure, I built one based on an encoder, and modified the soapbox accordingly, maintaining backward compatibility. This encoder based hand controller has its own arduino, and connects to the soapbox, and through it to the PC to receive commands from the desktop app — but this connection is optional, it is fully functional as a standalone device. Below is the block diagram, explaining how it optionally fits into the soapbox daisy chain. Most variables are hand tuned for the DC motor + reductor gear box in use, as the source code reveals.

(tovább…)

I’m posting because of a very frustrating issue I stumbled upon while developing my photo planner: php’s acos function has an undocumented (yet found by others) behavior. It can return NaN, in a way that breaks a JSON. The PHP manual says (2019-04-02) Return Values: The arc cosine of arg in radians — and nothing about a NaN scenario. Nothing. On forums, it can be found that the function returns NaN when the argument is out of the range [-1, 1]. And as it turns out, due to rounding errors in the float, this can happen. Very, very, very annoying.

I have the following lines of code, obviously for astronomy, calculating the arc distance, in degrees, from radec pairs, in degrees.

function arcdistdeg($ra1, $dec1, $ra2, $dec2){
  $cosA = sin(deg2rad($dec1)) * sin(deg2rad($dec2)) + cos(deg2rad($dec1)) * cos(deg2rad($dec2)) * cos(deg2rad($ra1 - $ra2));
  return rad2deg(acos($cosA));
}

And this function returned NaN for perfectly valid input values (around NGC 4103). So the obvious solution was to force the range with a safe_acos function, similar to

function safe_acos($n){ return acos(min(max($n,-1.0),1.0)); };

Very, very annoying.

Working with Renesas chips and the GUIX framework made me take a walk on  memory lane, a program I wrote almost two decades ago.