unidentified problem !!!!!

Thread Starter

lesin akbar

Joined Dec 16, 2007
30
I've built a circuit containing AT89c51 along with 7 relays( for AC switching), relay is driven by ULN2003(12v). and the microcontroller is serially interfaced with the system. Now evrything works smoothly for "sometime". After that what happens no idea. If the ckt is restarted it works again. What could be the problem ? Ive noticed this thing in two other circuit also , that is when AC controlling comes, microcontroller goes MAD. Could it be solved by some sought of sheilding and all. In the earlier projects when this thing happend we completly isolated (perfect isolation) the motors and the ckt, all went in vain. Any one can please guide me ???????????
 

SgtWookie

Joined Jul 17, 2007
22,230
Do you have bypass capacitors on the microcontroller? Is your power to the relays isolated from the ULN2003?

Energizing solenoids can draw heavy peak loads. Put a large cap across your relay supply bus. Watch out for reverse EMF spikes caused by de-energizing the relays.

Your power supply might be marginal. If your supply voltage to the uC drops too low, it will malfunction.
 

Thread Starter

lesin akbar

Joined Dec 16, 2007
30
The routing intensity graph shows just fine. Ive given two capacitors after 7805 viz (100micro 25v) and (.01pf disc) which is the controller supply. And the supply to the relay and ULN is taken from just before 7805 viz 12v, and already there is a 1000microf 25 v capacitor present. And the voltage at my MC shows 4.99v i think thats good. So this is how my circuit looks, now where to make the difference. Will i have to draw another supply for the relay circuit alone.???

No my power to relays is not isolated from ULN2003.
 

eeboy

Joined Sep 27, 2007
90
Just a thought...

Maybe your problem is not at all related to EMI issues. Have you debugged the micro to verify your program counter is not off in never never land indicating an issue with the code? Perhaps the bit of code associated with the AC control causes some sort of stack overflow? Might be worth a look...
 

jvjtech

Joined Jan 26, 2008
23
Where Sgt. Wookie recommends caps on the relays I would add reverse biased diodes, 1N4002 or 1N4118 or similar, across the relays to suppress back emf spikes as the relays release. I would also try removing the relays and add leds with the appropriate dropping resistor in their place. The modified circuit can then be alowed to run, with appropriately simulated inputs to see if it locks up the same way as the unmodified circuit. This might give you an indication of whether the relays, pcb layout, decoupling caps (the lack of), etc. are the source of your problem or whether you have a more serious design error in the hardware or software. Regards.
 

hgmjr

Joined Jan 28, 2005
9,027
The recommendations thus far have been provided without a schematic in hand. Is it possible to provide a schematic to assist us in guiding you through the troubleshooting effort?

hgmjr
 
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