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I have connected an array of 6V relays to one of the digital pins of my Atmega328 microcontroller via a driver ulN2803. I have connected two lights and one fan to the relays. The light bulbs seem to work completely fine but when I try to turn the fan off(especially when its on lower speeds) the microcontroller resets. Is this some kind of interference? I have broken the wire that goes to the regulator and fed it to the relay.

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  • \$\begingroup\$ What do you mean by your last sentence? What do you mean by "broken"? Can you post a schematic diagram of your circuit? \$\endgroup\$ – Ricardo Dec 23 '14 at 23:43
  • \$\begingroup\$ This sounds like supply dipped / brown out ... this indicates the supply is not big enough (in current capacity) to handle the almost stalling of the fan (a stalled electric motor is almost a short circuit .. maybe equivalent to 5 to 10 ohms) \$\endgroup\$ – Spoon Dec 24 '14 at 9:15
  • \$\begingroup\$ @Ricardo I disconnected the phase wire going to my fan regulator and connected it to the Common terminal of the relay and connected another wire between the NC and the regulator phase input. That is how i 'broke' the phase wire and fed it to the relay. Is this due to the regulator or something? When my regulator is off or when the fan is on full swing the relay retracts very well. Only when I reduce the speed via regulator this phenomena occurs. \$\endgroup\$ – Meet Desai Dec 24 '14 at 14:30
  • \$\begingroup\$ @Spoon I have connected a 6v 1A power supply, and there is no reason there is a power outage from the supply. The relay works totally fine when the fan is off or on full swing. So this looks more like and interference from the current that comes out of regulator. I fail to understand this. How do I eliminate this? \$\endgroup\$ – Meet Desai Dec 24 '14 at 14:32
  • \$\begingroup\$ What you need here is a scope to track down what the cause is. Both are possible. 6V with a motor pulsing a 5 ohm load across a supply (like a slow DC fan might present, try measuring the resistance) is 1.2A so your supply is not going to cope at those pulses.. however if there are 2 supplies ... with one just for the fan and one for everything else then you might be ok (Often in designs you see "dirty supplies" for relays, fans etc and "clean supplies" for MCU's etc). Interference is still possible but the supply dipping is removed. Also keep the circuits away from each other if possible... \$\endgroup\$ – Spoon Dec 24 '14 at 15:42
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Hey guys I figured out that the fan regulator was causing problem. Initially there was a Electrical regulator(resistance based) and now I have replaced with an Electronic regulator. However I have kept it for test and waiting for further results. As of now there is no reset after replacement of the regulator.

Thanks for your answers. :)

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