Dear all,

there is marble slicing machine which has failed controller. and for that i did mcu based controller this controller has the following inputs
plus button, minus button, enter button, proximity sensor input at mcu interrupt pin and limit switch input. the controller let user for adjusting the marble width adjustment. pressing the enter button start the controller normal cycle it start inching motor which moves the marble deck left or right. after the proximity sensor counts define number of revolution on the shaft the mcu stop the inching and start forward/backward motor which moves the deck forward or backward. but the mcu should check limit switch at either extreme of forward/backward move and should start the inching (the mcu only start the big motor switching of the motor is done with limit switch). the limit switch only tells the mcu that the big motor moves the deck to the extremes and it is switched off so that the mcu start inching again.

all the revolution counting and sequence is okay, but the big and confusing problem is : the mcu think as the limit switch depressed when only the big motor stopped, i thought it was due to electromagnetic interference and increase the redundancy of input checking but the problem remain the same.


i have attached the source code and rough schematics

 

It could still be interference.
Try removing BC109 and connecting the optocoupler directly to the mcu input.
Try 0.1uF on the input of the mcu.
Try changing the optocoupler to one that has 6 pins and you can put a resistor to the base of the transistor part of the optocoupler, that increases the stability by reducing the gain.

 

Yes alfonsom,
one thing that i didn't do is putting cap on the input side of the limit switch. but to minimize the interference i believe i did enough on the code side. in the code i repeatedly checked the input and i put enough delay between two consecutive input check which let the interfering signal enough time to fade away

don't you believe this coding remove interfering?

 

I believe that it is better to cut the interference at the source.