Here's a plc challenge.

— a traffic light program has 12 real-world lights. there are 3 for north, 3 for south, 3 for east, and 3 for west.

— the north and south work simultaneously while east and west work simultaneously, but opposite of north and south. (think of a real world traffic pattern)

— the red lights will be energized for 30 seconds.

— the yellow lights will be energized for 5 seconds.

— the green lights will be energized for 25 seconds.

— a maintained spst must be used to start the program running and will stop the program if opened at any time. (this switch operates as both the start and stop)

— if the program is ever stopped at any time during operation, to include loss of power, the sequence must start back up exactly where it left off without the use of any other input besides the one spst switch returning to the closed position.

— you are to keep a total count of cycles (green, yellow, red completion is one cycle) for maintenance purposes. the total count is to be reset with a momentary pb.

— you must use a minimum of 3 instructions, 1 math instruction, and 1 n7 integer file.

— you can only use 1 timer.

— total cycle count must be done without a counter.

good luck to whoever can get this!