Cat5 was installed for signal. What now?

Great, you’re back up!

3.9V is well within specs, 3.5V is getting marginal.
One thing I’ve tended towards on the TxRx pairs is to look for devices with protection diodes (and/or resettable fuses) on the +A/-B lines.
The differential lines can be good antennas to pick up all kinds of stray signals and while they usually will ignore that noise as far as the digital signal goes, they might possibly end up with induced voltage spikes that can fry the circuitry.
The longer the lines, the bigger the risk to the RS485 devices.

The other thing I’ve tended to are devices that have “auto-Tx” so you don’t have to set which device is Tx or Rx to make the config a little simpler. Those devices tend to have more protection circuitry as well, but are still cheap in bulk amounts. Just remember to enable the termination resistor on both devices.

It costs more than unshielded cable, but if shielded twisted pair cable is used, the shield prevents an electric field from coupling to the cable and the twists prevent magnetic interference.

Properly installed, STP will significantly reduce the amount of voltage coupled to a cable by things like a nearby (not direct!) lightning strike, or high power RF source. (e.g. radio/TV station)

The shield should be grounded at only one point to avoid a ground loop.

Hi all,

I’m in the process of fitting a pair of ttl to rs485 converters.
I getvthe vcc gnd DI RO etc but what does the RE DE mean when it says pull high or pull low?

Plus I moved my esp8266 so it only has a 50mm data line length and it worse than when it was 2m! Now flashes white before it goes to the colour I want when it powers up!

RE & DE control the direction of data for the MAX485 chip.
It’s actually ~RE and DE, meaning when the ~RE pin is Low it’s active and when the DE pin is High its active.

So for WLED operation, you tie ~RE and DE together to make a single direction control pin.
If the pin is Low, the device is a receiver (RX) and you get data out of RO for your LEDs.
If the pin is High, the device is a transmitter (TX) and you supply data in to DI.

And of course you must use these devices as pairs, a TX unit sending to an RX unit.