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I’ve just discovered a strange behaviour of a LED bulb (E27, 220v/AC) that I’m currently turning on/off via an 8-channel SSR relay. Such a relay module is powered with a switching power-supply, powering both the relay-module and an Arduino MEGA 2560. I also have a wall-push-button connected to an INPUT_PULLUP PIN of Arduino (one side) and to GND (the other side). Another OUTPUT PIN of Arduino is connected to the first channel of the SSR relay module (to handle the SSR connected to the LED bulb).

As for Arduino, I choose to power it trough the Vin.

As for GNDs, both Arduino and the relay module get the GND from the power-supply.

A very rough schema is reported below (please, don’t blame me for missing details. As for the driller, please ignore it for a moment!):

enter image description here

Such infrasctructure worked flawlessy for weeks, being powered on and correctly responding to push-button clicks without any issues.

Recently I needed to make an hole to a wall, actually a couple of meters away from the LED bulb, and at least 5/7 meters away from Arduino (Arduino, the relay module and the power-supply are located close to each other, in a box, under a staircase).

To make the hole I used an AC-powered driller (not a battery-powered one). Actually, it’s exactly the driller you can see in the image above).

What happened was that…. the LED bulb “flashed”, with a real quick “turn_on”/”turn_off” cicle. A single quick cicle.

This phonomena seems to be related to the “start” of the driller engine, more or less when the brushes inside the driller fires up some sparks (BTW: I’m supposing my driller is using brushes, inside).

I’ve spent some time investigating EMI, as electrical motors are known to be source of EMIs.

What I learnt so far is that:

  1. my problem is different from the (quite common, indeed) one that see a LED bulb “flashing” at a very fixed frequency (once every 20 seconds, for example) despite the fact that the SSR-relay is open. My BULB keeps staying OFF and… flash only when the drill is working (actually it flash with a random behaviour, but only when the driller is running);

  2. my SSRs, as well as almost any SSR, include a “snubber circuit“;

  3. if I unplug the power-supply, turning off Arduino as well as the “control-plane” of the SSR relay module… the phenomena PERSIST.

  4. if I unplug everything… the phenomena disappear (obviously?).

  5. if I use the driller very close to the SSR relay module (and Arduino, and the power supply), phenomena is exactly the same.

There are lots of things that I still need to investigate (starting from using “shielded” cables, as for the connections between Arduino’s PIN, push-buttons and relay modules) but… point 3) above makes me think that I’m missing some bigger problems: can the 10 meters long electrical wires between the LED bulb and the AC power source, acts like an antenna so to catch so much EMIs to “flash” the bulb?

Can someone help me in understanding what’s happening or, eventually, which is the proper “troubleshooting process” that I should put in place to (try to) solve this problem?


A final note: should you want to check by yourself the “phenomena”, feel free to give a look to this MP4 video (22 seconds for 5.6MB), where I asked my son to “shout” as soon as he saw the “flash” (that I cannot see, as I was close to equipments, slight far away from the room). The driller engine is, also, clearly audible.