Functionality
- I2C based communication bus
- Ability to gang 4 units on one bus
- I2C Address range 0x20-0x27, with pairs of addresses being allocated on each board. Addresses are jumper selectable
- 16 IO ports available and can be programmed at bit level for input or output
- Current limit resistors are placed on each output and a shorting bus wire on inputs
- 5VDC operation
Schematic
BOM
NOTE: I am not installing the Schottky diodes and external supply as VCC is obtained as part of the I2C bus.
PCB Vendor
The assembled boards are $41 (way too expensive), but the bare PCBs are $3 and maybe $5 in additional components. I assemble them myself.
http://www.modelrailroadcontrolsystems.com/iox32-version-2-0-32-line-i-o-expander/
Microchip Port Expander
I'm using the I2C variant. Datasheet is in the attachments section