Simple TTL logic tester

The original chip definition format based on Boolean formulas works nicely for simple gates, but it becomes a problem when clock-type events are needed, And those are abundant with the buffers, registers and latches.

The chosen solution is in some sense simpler than the formula-based pattern generation as it just is a list of state-definitions executed in a specific order. The state definition are the actual commands send to the Arduino, but with a numeric prefix to make them unique. Python reads the definition into a dict object and those want unique keys. Almost by accident it makes finding the offending definition easier in the error message.

Converted the I.C. definition to proper JSON, apart from the header and comments. Strip all lines starting with '#' and it should validate. See https://github.com/electrickery/logicTester for details. The header info is json-ified too, but not yet used.

The PCB for the Arduino Mega 2560 finally got populated and somewhat tested. The layout is not perfect and the result isn't quite fit for the promotion poster, but probably good enough for testing and usage. This project is just to make digital logic I.C.s testing easy, not to win beauty contests.

Some issues found with construction and testing:

• the LED resistor value of 330 ohm is way to low for the Arduino pins. It is changed to 3k3 ohm.
• the resistor arrays were hard to find and weren't the designed size, so some extra resistors were needed to fill the missing positions. It would look better if all positions were discrete resistors.
• The MOSFETs ordered had a different package than the PCB design.

The next stage is:

• to test the board,
• add more and larger I.C.s to the library,
• implement test algorithms for tri-state, open collector, ...

At one time I might upload an updated schema and PCB, but as long as the current design is fixable, I won't order and test it.

There are five pins were power can be applied, being the highest pin number for 14, 16, 20, 24 and 28 pin I.C.s. For different power pin schemes, the breadboard solution of the prototype could be used.