Although arduino might not be up to the task... Looking at my fluke network cable tester made me wonder if a graphical TDR meter might work to identify working/non-working bulbs in a christmas light string. Likely won't undertake such a task even if it's feasible but what are your thoughts? Could a TDR find each bulb?
If the lights were in series it could work. But I think that they tend to be parallel these days and all I'd expect would be to get the length of the string.
If they are incandescent bulb type light strings then they are usually in series and in theory a TDR should spot the break.
Most modern christmas lights are LED, they are normally in a parallel arrangement and TDR aint going to work well.
I would be happy to test if the network tester was someone elses ..........................
Actually, it is true of both the incandescent and LED Christmas light strings, that they are in series-parallel, that is to say a number of strings in parallel, each of several lights.
This in regard to those operating at something like 33 V from a (switchmode) “transformer” and suitable for outdoor as well as indoor use. Haven’t seen the direct mains powered sets for some time.