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18F2550 external interrupts

 
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eng.mohamedtoumi



Joined: 13 Jan 2018
Posts: 20
Location: Tun

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18F2550 external interrupts
PostPosted: Fri May 11, 2018 6:28 pm     Reply with quote

hello... I've recently started a 18F2550 project consisting of a line follower robot using 18F2550.
I used 2 pull ups (as the PCM schematic with 4.7k resistor) as line sensors just for the purpose of debugging the code.
The line sensors are on external interrupts and working fine on real PCB (external interrupt is detected whenever i press the button).
Simulation works fine also.
Everything works fine on the pcb without the motors (2 motors each consuming 5v 0.8 A). I used a Bluetooth module to debug the sensors values and they were received correctly, but when i connect the motors the interrupt routine is started automatically even when i don't press the buttons.
PS: I checked the buttons and they are fine also I'm using a 5v 12A power source.
temtronic



Joined: 01 Jul 2010
Posts: 6152
Location: Greensville,Ontario

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PostPosted: Fri May 11, 2018 8:12 pm     Reply with quote

Welcome to the 'fun' world of EMI ! It sounds like the motors are generating EMI (noise) and triggering the PIC.
Some possible cures are
1) adding some .1 mfd caps near the VDD/VSS pins of the PIC
2) adding flyback diodes across the motor terminals
3) add a cap across the motor terminals
4) use Google to look for 'motor supression', or similar keywords
5) increase the PCB traces for power lines
6) wiring should be
power source---motors---PCB with PIC
7) add more C to power supply, esp. .1 mfd, .01 mfd (hf filters)

just some of the things you can/need to do.
Jay
eng.mohamedtoumi



Joined: 13 Jan 2018
Posts: 20
Location: Tun

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PostPosted: Sat May 12, 2018 6:13 am     Reply with quote

Thank you for your response. I will try your solutions. I'll post the results later. Cool Cool
eng.mohamedtoumi



Joined: 13 Jan 2018
Posts: 20
Location: Tun

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PostPosted: Sat May 12, 2018 9:07 am     Reply with quote

https://www.pololu.com/docs/0J15/9
this solution (connecting 3 cap to the motor) solved my problem Very Happy Smile
temtronic



Joined: 01 Jul 2010
Posts: 6152
Location: Greensville,Ontario

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PostPosted: Sat May 12, 2018 9:35 am     Reply with quote

GREAT, happy you got it fixed !!
EMI (noise) can be very hard to locate and suppress, entire books have been written on the subject and a lot of it is a 'black art' !
You may want to add .1 mfd caps to every I/O point (external connection) just to be sure...
Cheers
Jay
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