Hi I made PCB with arduino uno. It has inputs push-buttons, temperature sensor and four outputs (mechanical relay).The PCB has input stage transformer 220/12 V. It has voltage regulator 5V with two block capacitors of 100 nF (placed on input and output of voltage regulator). Also has electrolytic capacitor 4700 uF. The mechanical relays switch the three contactors with coil voltage of 220 VAC. All works fine. Only sometimes when all contactors switch off in the same time the ATMEGA328 resets by itself. It is because of the collapsing electromagnetic filed.I search the web and I found that I must put on the voltage regulator in parallel three block capacitor of 1,10,100 nF. Also in parallel of the coil of the contactor I must put the capacitor of 0,22 uF , 500V . Also near the uC I will put in parallel three block capacitors of the 1 , 10 , 100 nF. Is this is enough for block the noice which resets the uC or I must do additional things. Regards Riste
You are driving inductive loads there will be lots of kick back voltages generated when they switch off That will get into the supply of the Uno even after the voltage regulator causing brown outs and resets. There is plenty about this in the web Have you looked at/taken any of the advice there
1) Do you have quench diodes across the coils of the relays driven by the Uno? 2) Are the relays optically isolated from the Uno with their own power supply line? 3) do you have spark quenching capacitor resistor series combination across the contacts of these relays?
You need all of these plus probably some ferrite beads on the wiring and a good physical separation between any mains and inductive circuits before you stand a chance! RFI is a nightmare best of luck