Pc and microcontroller rs232 correspondence blunder when 220v contactor switches

Thread Starter


Joined Mar 19, 2022
Dear all, I am doing an undertaking wherein pc and atmega32 convey by means of rs232. The microcontroller convey level message and furthermore get order to impel 220v contactor.
All is well until I interface the transfers to drive the contactor I have checked electrical confinement between the board and the high volt, it is alright.

The issue happen haphazardly when the contactor switch. At the point when the issue happens the microcontroller won't reset it actually acknowledge order from the pc yet it will quit giving information to the pc through rs232. To settle this I attempted to close and return the sequential port automatically when the issue happens however the issue not tackled the issue possibly disappears when I restarted the microcontroller.

The wellspring of the issue appears to be electromagnetic commotion however I have done a microcontroller board which controls 220v burdens easily. The main contrast here is the microcontroller speak with PC and with each other microcontroller. Likewise tbe code is composed with arduino ide with atmega modules.

John P

Joined Oct 14, 2008
You haven't explained how the contactor is actually switched. Try an experiment where you switch the contactor with no 240V power applied. Does the problem still happen? If it does, then there's something in the way that you control the contactor that's causing it, and it's not related to the 240V power or the load that it drives.

But if it happens when the 240V power is switched, can you do anything to reduce sparking at the contacts when the relay switches, or could you use a solid-state relay? Can the processor simply be located farther away?


Joined Jul 18, 2013
When I have experienced noise on contactor switching, especially if AC coil is the lack of coil R/C 'Snubber' (AC) or BEMF diode (DC).

Thread Starter


Joined Mar 19, 2022
Dear All,
Presently, l am chipping away at an undertaking where l need to separate the drove conduct because of light or variety force. The point is to distinguish the finish of blur in/out and the start of slow squinting in consecutive cycles. l need to distinguish how long blur in/out and slow flickering proceeds.

the utilizing photoresistor with Arduino in circle cant help to recognize the stage when the worth of obstruction blur in/out is
395-281-369-291-124-88-125-288-320-387-395-291-116-217-308-359-385-263-330-301-120-75-117-258-327-385-395-281-369-291-124-88 and slow flickering 341-396-403-406-408-154-36-24-18-15-340-396-403-407-408-157-36-24-19-14.
Another strategy l have utilized is to interface the photoresistor to the capacitor for working out the time distinction for stimulating the capacitor when the photoresistor is high less time or low additional time expected to invigorate the capacitor. this way assisted a tad with getting more precise qualities yet separating them isn't sufficient.

l think the most effective way is utilizing beat width regulation however l need to change light or variety power over to voltage. Which gadget or part can assist with taking care of this issue?
l would be cheerful in the event that somebody can share his/her experience or thoughts for tackling this issue.


Joined Jun 5, 2013
We need to see s circuit for how the contactor is driven.

And, it would help if you could get someone to help you with your English. Your second post is totally incomprehensible.