Swapping out the arduino with TM may or may not fix your issue. And it's probably going to be expensive to do. If it comes to that, I'd suggest talking to Viasue (full disclosure they're my partner). He offers a dead strip solution that is arduino based. If you do that you might want to bring me into the loop. If it turns out it is the arduino, then obviously his product wouldn't work either and the two of you would have to work out a refund model which would be very unusual for him. Does TM offer a dead strip solution? What if you buy TM and have the same issues?
But before any of that I'd try troubleshooting in small steps. If you can prove its the relay that would go a long way. Try removing input power to the relay. Did that fix it? Put it back and try removing just output power. Obviously lap counting won't work, but did it fix the TV?
If it's the relay, you can buy a relay like the one TM provides and see if that fixes you. If it does great, if it doesn't then buying TM won't solve your problem and you'll be out a bunch of money.
If going small doesn't figure it out, I'd replace just the dead strip as the next small step. I've never heard of using a relay like this (very cool by the way), and there are other ways to do the same thing without a relay.
I'm not very good with interfaces so maybe everything I've said here should be ignored. But that's my two cents.
Indeed, I agree with Dave, the idea is that I constantly update and try new things with Arduino and RC, that's what I love about this.
Yesterday my partner brought his laptop and it seems that the problem stopped as far as we saw. I'm starting to believe it's my computers problem, that it's too sensible to this kind of interference because I installed the capacitors like the ones in the Scalextric cars and it just helped a little bit, but it's hard to tell. I installed them at the output and input of the relay board to the arduino. But when I changed the computer it aparently stopped. I was using a mini pc:
I'll do more testing today, we had a big race and we preffered to run with a blinking tv rather than a RC unconfigured version where we were having issues with the arduino driver, so now that I got more time I'll check and tell everyone what happened.
I believe this problem could also be solved if I used solid state relays to avoid this interference from having 2 four channel normal relays boards clicking at the same time:
Also thank you to RichD, the text was a very helpful.