MCP23008 IO Expander - ULN2803 8 Channel Darlington Sink Drivers

Now that the MCP23008 toggle port functions look OK, I am moving on to the ULN2803 board.  

The ULN2803 board consists of 3 basic things.

1. The HC573 buffers 8 bit output of TLP521-4.  HC573 output then goes to the HC04 hex inverter.  The TLP521-4 inverts once, so when HC04 inverts again, MCP23008 output then keeps the original polarity.

The MCP23008 output, so after HC573 buffered once, optically isolated, and logical level shifted by TLP521-4, then buffered again by another HC573, then inverted again by HC04, then finally the results go to the input of ULN2803.

Next step is to see if MCP2803 can indirectly drive the ULN2803.

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