interference

Thread Starter

fisho

Joined Nov 4, 2008
18
Hi there

I recently built a Pic16f84a controller for laundry machine.but every time a contactor makes and breakes the micro resets. tried a pi filter at the mains input but it didn't help.a simple glitch resets the micro. pls help. regarding the snubber diodes u asked there are the fools diode across each relay coil. like i stated i've no problem with the relays. they don't disturb my circuit.
 
Last edited:

thatoneguy

Joined Feb 19, 2009
6,359
Do you have a snubber diode across the coil of the contactor (relay)?

Do you have decoupling caps at the uC to hold the power supply steady during load switching?
 

Thread Starter

fisho

Joined Nov 4, 2008
18
dear sir;
I have a regulated pwr supply(7805 + 100nf filter; main filter cap is 2200mfd) i've also put a100nf cap near the vdd pin of the MCU as recommended. the contactors are driven via relays.the relay circuit is optoisolated from the MCU.the relays switch in and out and no problem. the problem appears as the main 220v contactor energizes and drops.
 

thatoneguy

Joined Feb 19, 2009
6,359
Do you have a digital scope or other logging device to watch the voltage on the input and output of the 7805 during the load switches?

An over/under voltage glitch could be causing the 7805 to momentarily block output.

What is the input to the 7805?

Is the controller physically near the relay or power lines? If so, it in an enclosure with any shielding?
 
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Thread Starter

fisho

Joined Nov 4, 2008
18
well the input is over 12.5v DC.the pwr supply is far from the micros.
the amazing thing is that plugging into a remotely located socket outlet
any kind of load disturbs the micro. my expectation is for some reason the
MCLR line althogh tied to Vdd via 1K may dip and reaset the micro.still confused.
 

Kermit2

Joined Feb 5, 2010
4,162
Verify the presence of an earth ground at the AC socket. If the powersupply is floating with respect to ground, all kinds of strange things can happen.
 

thatoneguy

Joined Feb 19, 2009
6,359
well the input is over 12.5v DC.the pwr supply is far from the micros.
the amazing thing is that plugging into a remotely located socket outlet
any kind of load disturbs the micro. my expectation is for some reason the
MCLR line althogh tied to Vdd via 1K may dip and reaset the micro.still confused.

Can you post a photo of your circuit board, front and back?
 
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