04-03-2018, 18:15
(04-03-2018, 12:14)garybb1 Wrote: As I understand it if I want to use a longer cable run I have to use the SHT21/EI2C terminals on the TX board.
That's correct.
(04-03-2018, 12:14)garybb1 Wrote: The schematic shows a 5V supply at this terminal but the data sheets for the SHT21 show the max voltage this device can handle is 3.6V so I was worried I might damage the SHT21
What matters is if the module where the your SHT21 is installed, is suitable to be powered by 5V or not. All SHT21 chip are 3.3V, so its the module that have some extra components to act as level converter.
Check the specs of the module you have. If it says that can be powered by 5V, you can use it safely.
Post a picture of you module, it may help.