noise problem?

powerstyle · Guest

Hii everybody !!!

I constructed a power device using PIC16F877 and some thyristors. It regulates the line voltage to 220 volts in every cycle . Everything was OK at home for hours, but whenever I took the device to a workshop in which lots of machines were running and stopping from time to time, it got stuck ramdomly , WDT worked and afterwards PIC reset. So thyristors got turned off undesirably.

Then I took the device back to home, I touched the ground of the control circuit with PIC by a screwdriver, it reset again.(not always but sometimes!)

when I used (for example) a vacoom cleaner on the same plug (input) or output of the device it rarely got stuck unfortunately.

Control circuit with PIC is completely isoleted from tyristor triggerring (drive) circuits and line potential.

What should I do?
How can I deal with this noise problem?

thanks indeed for every reply.

powerstyle

valemike · Guest

In noisy environments, we use a power line filter - e.g. Schaffner FN406-8.4A.

Also, you might want to put a .1uf capacitor on the PIC's MCLR, in addition to the pullup resistor (10k?) to Vdd. This supposedly prevents noise from resetting your PIC.

I'm not a hardware guy, but i'm just sharing what has been done to the systems i've programmed to protect against such noise.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

These sorts of problems can be tough! Half the battle is just finding out how to replicate the problem. What PIC are you using and what reset circuit is on it? These days I almost always just stick on a MAX809 reset chip. Some designers opto-isolate all inputs and outputs. But I find that is usually overkill, and if not done correctly it doesn't even fix the problem.

Is there any way you can give us a link to your schematic?
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Guest · Posted: Sat Feb 12, 2005 10:38 pm

Sherpa Doug · Guest

"Guest" dares not reveal his name while accusing me of cowardice!

From the unrepentantly blue state of Massachusetts,
Sherpa Doug

Yashu · Joined: 08 Oct 2003 Posts: 26

What's your brownout detect config bit burned to?

Also, must agree with valemike's common mode choke recommendation.

pat · Joined: 07 Sep 2003 Posts: 40 Location: Adelaide, Australia

Doug,

Can you please explain the befefits of the MAX809? The PIC already has a 72ms (I think) power up timer, so what does the MAX809 do?

Thanks

Pat

pat · Joined: 07 Sep 2003 Posts: 40 Location: Adelaide, Australia

This may be a case of RTFDS (read the F... data sheet) first

It says

powerstyle · Guest

The answer is at the address below

thanks everybody

http://forum.microchip.com/tm.asp?m=35930