blinkingLight example

Hi Wouter

SimPyLC, or in fact any PLC works with discrete time steps. So the time will be the exactly the same in the whole sweep (cycle).
This means that if the timer is reset, it will stay zero from that point to exactly the end of the sweep, which in this case suits the purpose.

While it's not needed here, a oneshot can be useful if the reaction on the timer being 0 has to take place EARLIER in the sweep.
This is because a oneshot stays True exactly one cycle, so not until the end of the sweep, but exactly upto the point where it was triggered.
If say it was triggered in line 20 of the code of your sweep, it will stay True exactly until execution is again at line 20.
So every circuit is guaranteed to see the oneshot being True EXACTLY ONCE.

When running your code on an actual Arduino rather than only on the simulator, the use of oneshots is more often required, due to limititations on the Arduino's timer resolution.
From the SimPyLCHowTo that's in the distro:



Remark: The resolution of timers on the Arduino has been improved, but the problem may still occur, so using oneshots in this case remains a good idea.

Concerning the light staying dark: Turns out that there's a subtle difference between Python 2.7 and 3.5, namely the __nonzero__ magic word being replaced by the __bool__ magic word.
I've adapted this in engine.py so the blinkinglight works fine now.
This fix is in SymPyLC 3.5.3.


Kind regards
Jacques