The remote display driver board provides the RS232 to 3.3 volt logic conversion for the Nextion display in addition to routing +5 VDC power to the display and the signals from the remote rotary encoder back to the HMI.
This board comes fully assembled. The builder only needs to purchase a rotary encoder as shown on the BOM and wire it with the supplied Dupont female jumpers so it can be plugged into the display board. The Nextion display comes with jumpers ready to use.
CAUTION: Keyed connectors are not used on this board so it is possible to connect the display and encoder incorrectly! The header pins are clearly marked. Make sure you connect them correctly. If you reverse the +5 VDC and ground wires on the Nextion display you will damage it!
The circuit is extremely simple. The Nextion display runs on +5 VDC. The HMI provided this voltage on pin 8 of J1. U1 regulates the +5 VDC down to 3.3 VDC for IC1 which provides the RS232 to 3.3 volt logic conversion for the display. The rotary encoder simply connects to J1 through RF filters comprised of ferrite beads and bypass capacitors. I know, the ferrites aren’t doing anything since they’re normally looking into open circuits. They will be removed in the v3.1 update for this board. 🙂