i have a problem with this pcb. anyone can explain component on blue circle ??
That is a 5v relay and connections for an external limit switch. When the limit switch is closed, the relay clicks thus killing power to your motors.
We have asked you once to please put a little effort into your questions. Here we are again, with a one-word title (one that does not explain the problem, nor is any help to any future searches). Please show you deserve the help you are getting by putting a bit more effort into your posts.
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kipas = Traditional folding fan preferably made of hardwood or iron.
:) just messing with you.
I was wondering about that kipas myself...
I was wrong (well, a little)--when the limit switch is connected, it may be a NC or a NO, I don't know which. I would assume it is a NC, because your L293D is connected to the NO side of your relay. Thus, if your limit switch was a NO, your motors would only run WHEN the limit switch was clicked. That would be a "go ahead" switch, not a limit switch.
As it stands now, and assuming the limit switch kills the motors, then the limit switch is NC, the L293D goes to NO on the relay and the normal function is to keep the relay clicked during operation.
Then again, I don't have a whole lot to work from here, so I could be way off.