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I am making an automation device. I am using an atmega8a to control 6 relays. The setup is standard, 220v load, 5v dc coil, flyback diode and an NPN transistor to trigger with atmega pin. The problem is when I turn ON the relay, there is 10-20 MHz noise on the DC side and the atmega restarts. Switching OFF relays doesn't create a problem. i am guessing this is happening because of EMI. Is there a way i can protect my atmega from this and not have it restart everytime I start a relay.

The SMPS is 5v 2A

I have star tracks from SMPS

Is there a way to solve this?

  • Add a snubber circuit. – Majenko Jul 24 at 16:36
  • @Majenko where? acrross contacts? or across load? – Ujjwal Syal Jul 24 at 17:06
  • Across the contacts of the relay. – Majenko Jul 24 at 17:27
  • @Majenko any recommended values? – Ujjwal Syal Jul 24 at 19:03
  • Nope, no clue. Take an example from a similar situation and try it. – Majenko Jul 24 at 19:11
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This can also be a power shortage as there will be a drop when the relays turn on, depending on you psu it might not respond quick enough, so you get a brown out. I added a bit 4700uF cap on the psu power line to the arduino.

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