Thanks. I've tested my RX/TX pins with both LEDs (with resistor) AND with a test sketch which involved sending data over serial from a host PC and getting a reply back from the device.That all works.
So back to attempting to get the DFPlayer Mini working - I've tried using a Core, and a Photon. I've tried using two different DFPlayer Minis. I've tried two different USB cables. I can no longer get the DFPlayer Mini to play nicely with a Core or a Photon.
The only way I can get my code working is to completely remove the DFPlayer Mini code from my sketch. This is code that's worked on about eight other Particle devices, both Cores and Photons and never given me any trouble once I got it working initially.
I'm clutching at straws here, but has anything changed in firmware v1.0.0? I don't get compiler errors but I do now get freezing devices which I didn't before. I've now spent three evenings trying to debug this and I'm pulling my hair out somewhat.
Thanks!
EDIT: Just tried
this sketch from FiDel and it works. The MP3s on the SD card play in sequence one after the other. So confused. When I use my code now (even when targeting older versions of the firmware), it now no longer works.