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Assembling the board

The printed circuit board is designed so you can chose the desired configuration of GPIOs by mounting the appropriate components for each circuit. For GPI, mount the opto isolator and the two associated resistors. For GPO, mount the relay and the associated diode. Never mount the two of these options in the same GPIO circuit.

You are not forced, though, to use opto isolators for inputs or relays for output. If a direct connection is desired, replace those components with jump wires (pins 2,4 of the opto isolator footprint). If it is an input, you may want to also mount the 10K pull up resistor.

The RS485/422 driver (U2) is optional. If you don't plan to make use of the serial port, you can leave the footprint empty as well as that of the header connector J2. Same with the ADDR header (S1) if you have no plans for configuration jumpers.