Relay board crashing Arduino

Hi all. We've all seen those snazzy indicators developed by Audi (which have now been copied by Mercedes, Iveco, Volvo and so on) which sweep out when the indicator is activated. Well funnily enough, I like the idea too, and my car didn't come with them, so I thought I'd home-brew it.
I know kits are available to buy but they're usually quite generic and don't enable you to set your lights up as you like, so I set about producing a workable solution for myself.

The setup is very basic - Arduino Uno and a 4-relay board connected to amber LED modules. The modules sweep beautifully just as expected.. for about 10 seconds. Then the board crashes, either freezing completely, or chattering the relays as quickly as it can on an infinite loop.

I don't understand why. I have tried different power sources (battery, mains-powered PSU etc) and even reversing the loading by making the LED modules powered up at the start and switching them off as the sweep is done. (this is how it appears in the example video I have linked)

Any insights as to why my board crashes mid-execution on this project?

Watching a video is not important at all as to why you have the problem. A schematic of how you have all this wired together and how you are powering it is the only thing that will help debug this.

Paul

I guess you power the Uno with 12volt on the DC socket or the V-in pin.
And draw power for the four relays from the 5volt pin.

The 5volt regulator on the Uno will shut down if you draw more than ~100mA from the 5volt pin when powered from 12volt. Four relays (~300mA) and the Uno itself (~50mA) will overheat the regulator in seconds.

An easy solution is to power relays and Uno from a car cigaret lighter type USB phone charger (with a USB lead).
Leo..