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will PIC work in adverse circumstances

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sijincool

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i had to use a pic16f873a along with a transformer(6A) in the same case(metal box).for controlling a set of relays(5A,12V).
the functional test was ok and it worked fine in the lab for 4 days continously but when it is released as aproduct we continously got complaints of "PIC hangs".

when it is reset the system works fine again.

my question is would there be any interference in the working of PIC due to the magnectic field/or temperature(in lab we tested upto 60 degrees)/power fluctuations.

or what else may be the problem

pls help me
thanks in advance
 

Hi,
Noise may be affecting the PIC if it is not well decoupled. Or if the power supply is not well filtered (there is too much ripple).

Hope this helps.
Tahmid.
 

    S

    sijincool

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Noise can effect any digital circuits and a microcontroller is no exception.

1. Place decoupling capacitors on the powersupply pins of the microcontroller as
close as possible to the chip.
2. Another important thing to consider when switching relays is to use a recirculation
diode with the relay, otherwise the flyback voltages may reset/hang the
microcontroller.

If it is possible to share the schematic of you circuit then i may be in a better position to help.

Regards.
 

    S

    sijincool

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PIC devices are ver sensitive and highly affected by EMI's and RFI's. I have personally faced similar problems as you.
 

thanks for the reply.

i have already checked it.

1)i used filter capacitors as u said
2)used 1n4007 flayback diodes even though i am using a uln2003D (they say inbuild fly back diode)
3) grounded all unused pins
4) grounded the body of Xtal oscilator

still the problem remains.

:(

Added after 3 minutes:

is there any solutions.

like any other microcontrollers...


one more thing i noted is that iam currently using the DIP pic package.

in some SMD packages they label it as industrial.

will it solve my problem???
any guess?
 

I think that the problem lies with the design and not with the MCU or package.
What is the value of pull up resistor on the MCLR pin?Have you decoupled the MCLR pin through a capacitor?Have you enabled Brown out detect? What is the frequency of the oscillator that you are using?
The layout of the oscillator section on the PCB is also critical.
Regards.
 

sijincool said:
in some SMD packages they label it as industrial.

will it solve my problem???
any guess?
Click to expand...

No. That is simply a wider temperature range version.
 

HI

I order to mak it works well in an out side the LAB environment you will need to add some protection components:

1) Add a reset and watch dog external IC - like TPS3828 from TI
(also remember to hit the watch dog so he want barks and reset your micro)

2) Add decoupling capacitor on every VCC pin of the micro

3) Add some Bead inductor in series with the power line who feed the micro

All the best

Bobi

The microcontroller specialist
 

    S

    sijincool

    Points: 2
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Also you may consider using optocouplers at the outputs of the MCU, used for switching relays. Put them between MCU's outputs and ULN2003.
 

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