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Using just NAND gates requires too many of them. See http://www.neuroproductions.be/logic-lab/index.php?id=63191 for the unfinished work in getting a full chip to work.

Printed Circuit Board

A PCB has been laid out (just in case Tony's prototype works).

Main points

• A letterbox slot has been made in the centre of the HD1, HD2, (which are connected both sides,) so that either direct soldering or wire links may be used to connect the signals from the 512K/512K card to the PCB.
• The pads of the footprint of the SOT-23-5 have been made longer, to enable easier soldering of the small parts.
• The bottom Left Hand corner of the PCB matches the shape of the 512K/512K Card for easy alignment.
• C2 on the 512K/512K, needs to be removed and put onto the PCB, in the same space. This is to make the PCB a bit larger for stability.

The 7 layers

Here are the layers printed on A4 sheets. The board is small, zooming in is generally helpful.